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1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * procarray.c
4 : : * POSTGRES process array code.
5 : : *
6 : : *
7 : : * This module maintains arrays of PGPROC substructures, as well as associated
8 : : * arrays in ProcGlobal, for all active backends. Although there are several
9 : : * uses for this, the principal one is as a means of determining the set of
10 : : * currently running transactions.
11 : : *
12 : : * Because of various subtle race conditions it is critical that a backend
13 : : * hold the correct locks while setting or clearing its xid (in
14 : : * ProcGlobal->xids[]/MyProc->xid). See notes in
15 : : * src/backend/access/transam/README.
16 : : *
17 : : * The process arrays now also include structures representing prepared
18 : : * transactions. The xid and subxids fields of these are valid, as are the
19 : : * myProcLocks lists. They can be distinguished from regular backend PGPROCs
20 : : * at need by checking for pid == 0.
21 : : *
22 : : * During hot standby, we also keep a list of XIDs representing transactions
23 : : * that are known to be running on the primary (or more precisely, were running
24 : : * as of the current point in the WAL stream). This list is kept in the
25 : : * KnownAssignedXids array, and is updated by watching the sequence of
26 : : * arriving XIDs. This is necessary because if we leave those XIDs out of
27 : : * snapshots taken for standby queries, then they will appear to be already
28 : : * complete, leading to MVCC failures. Note that in hot standby, the PGPROC
29 : : * array represents standby processes, which by definition are not running
30 : : * transactions that have XIDs.
31 : : *
32 : : * It is perhaps possible for a backend on the primary to terminate without
33 : : * writing an abort record for its transaction. While that shouldn't really
34 : : * happen, it would tie up KnownAssignedXids indefinitely, so we protect
35 : : * ourselves by pruning the array when a valid list of running XIDs arrives.
36 : : *
37 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
38 : : * Portions Copyright (c) 1994, Regents of the University of California
39 : : *
40 : : *
41 : : * IDENTIFICATION
42 : : * src/backend/storage/ipc/procarray.c
43 : : *
44 : : *-------------------------------------------------------------------------
45 : : */
46 : : #include "postgres.h"
47 : :
48 : : #include <signal.h>
49 : :
50 : : #include "access/subtrans.h"
51 : : #include "access/transam.h"
52 : : #include "access/twophase.h"
53 : : #include "access/xact.h"
54 : : #include "access/xlogutils.h"
55 : : #include "catalog/catalog.h"
56 : : #include "catalog/pg_authid.h"
57 : : #include "miscadmin.h"
58 : : #include "pgstat.h"
59 : : #include "postmaster/bgworker.h"
60 : : #include "port/pg_lfind.h"
61 : : #include "storage/proc.h"
62 : : #include "storage/procarray.h"
63 : : #include "utils/acl.h"
64 : : #include "utils/builtins.h"
65 : : #include "utils/injection_point.h"
66 : : #include "utils/lsyscache.h"
67 : : #include "utils/rel.h"
68 : : #include "utils/snapmgr.h"
69 : :
70 : : #define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var))))
71 : :
72 : : /* Our shared memory area */
73 : : typedef struct ProcArrayStruct
74 : : {
75 : : int numProcs; /* number of valid procs entries */
76 : : int maxProcs; /* allocated size of procs array */
77 : :
78 : : /*
79 : : * Known assigned XIDs handling
80 : : */
81 : : int maxKnownAssignedXids; /* allocated size of array */
82 : : int numKnownAssignedXids; /* current # of valid entries */
83 : : int tailKnownAssignedXids; /* index of oldest valid element */
84 : : int headKnownAssignedXids; /* index of newest element, + 1 */
85 : :
86 : : /*
87 : : * Highest subxid that has been removed from KnownAssignedXids array to
88 : : * prevent overflow; or InvalidTransactionId if none. We track this for
89 : : * similar reasons to tracking overflowing cached subxids in PGPROC
90 : : * entries. Must hold exclusive ProcArrayLock to change this, and shared
91 : : * lock to read it.
92 : : */
93 : : TransactionId lastOverflowedXid;
94 : :
95 : : /* oldest xmin of any replication slot */
96 : : TransactionId replication_slot_xmin;
97 : : /* oldest catalog xmin of any replication slot */
98 : : TransactionId replication_slot_catalog_xmin;
99 : :
100 : : /* indexes into allProcs[], has PROCARRAY_MAXPROCS entries */
101 : : int pgprocnos[FLEXIBLE_ARRAY_MEMBER];
102 : : } ProcArrayStruct;
103 : :
104 : : /*
105 : : * State for the GlobalVisTest* family of functions. Those functions can
106 : : * e.g. be used to decide if a deleted row can be removed without violating
107 : : * MVCC semantics: If the deleted row's xmax is not considered to be running
108 : : * by anyone, the row can be removed.
109 : : *
110 : : * To avoid slowing down GetSnapshotData(), we don't calculate a precise
111 : : * cutoff XID while building a snapshot (looking at the frequently changing
112 : : * xmins scales badly). Instead we compute two boundaries while building the
113 : : * snapshot:
114 : : *
115 : : * 1) definitely_needed, indicating that rows deleted by XIDs >=
116 : : * definitely_needed are definitely still visible.
117 : : *
118 : : * 2) maybe_needed, indicating that rows deleted by XIDs < maybe_needed can
119 : : * definitely be removed
120 : : *
121 : : * When testing an XID that falls in between the two (i.e. XID >= maybe_needed
122 : : * && XID < definitely_needed), the boundaries can be recomputed (using
123 : : * ComputeXidHorizons()) to get a more accurate answer. This is cheaper than
124 : : * maintaining an accurate value all the time.
125 : : *
126 : : * As it is not cheap to compute accurate boundaries, we limit the number of
127 : : * times that happens in short succession. See GlobalVisTestShouldUpdate().
128 : : *
129 : : *
130 : : * There are three backend lifetime instances of this struct, optimized for
131 : : * different types of relations. As e.g. a normal user defined table in one
132 : : * database is inaccessible to backends connected to another database, a test
133 : : * specific to a relation can be more aggressive than a test for a shared
134 : : * relation. Currently we track four different states:
135 : : *
136 : : * 1) GlobalVisSharedRels, which only considers an XID's
137 : : * effects visible-to-everyone if neither snapshots in any database, nor a
138 : : * replication slot's xmin, nor a replication slot's catalog_xmin might
139 : : * still consider XID as running.
140 : : *
141 : : * 2) GlobalVisCatalogRels, which only considers an XID's
142 : : * effects visible-to-everyone if neither snapshots in the current
143 : : * database, nor a replication slot's xmin, nor a replication slot's
144 : : * catalog_xmin might still consider XID as running.
145 : : *
146 : : * I.e. the difference to GlobalVisSharedRels is that
147 : : * snapshot in other databases are ignored.
148 : : *
149 : : * 3) GlobalVisDataRels, which only considers an XID's
150 : : * effects visible-to-everyone if neither snapshots in the current
151 : : * database, nor a replication slot's xmin consider XID as running.
152 : : *
153 : : * I.e. the difference to GlobalVisCatalogRels is that
154 : : * replication slot's catalog_xmin is not taken into account.
155 : : *
156 : : * 4) GlobalVisTempRels, which only considers the current session, as temp
157 : : * tables are not visible to other sessions.
158 : : *
159 : : * GlobalVisTestFor(relation) returns the appropriate state
160 : : * for the relation.
161 : : *
162 : : * The boundaries are FullTransactionIds instead of TransactionIds to avoid
163 : : * wraparound dangers. There e.g. would otherwise exist no procarray state to
164 : : * prevent maybe_needed to become old enough after the GetSnapshotData()
165 : : * call.
166 : : *
167 : : * The typedef is in the header.
168 : : */
169 : : struct GlobalVisState
170 : : {
171 : : /* XIDs >= are considered running by some backend */
172 : : FullTransactionId definitely_needed;
173 : :
174 : : /* XIDs < are not considered to be running by any backend */
175 : : FullTransactionId maybe_needed;
176 : : };
177 : :
178 : : /*
179 : : * Result of ComputeXidHorizons().
180 : : */
181 : : typedef struct ComputeXidHorizonsResult
182 : : {
183 : : /*
184 : : * The value of TransamVariables->latestCompletedXid when
185 : : * ComputeXidHorizons() held ProcArrayLock.
186 : : */
187 : : FullTransactionId latest_completed;
188 : :
189 : : /*
190 : : * The same for procArray->replication_slot_xmin and
191 : : * procArray->replication_slot_catalog_xmin.
192 : : */
193 : : TransactionId slot_xmin;
194 : : TransactionId slot_catalog_xmin;
195 : :
196 : : /*
197 : : * Oldest xid that any backend might still consider running. This needs to
198 : : * include processes running VACUUM, in contrast to the normal visibility
199 : : * cutoffs, as vacuum needs to be able to perform pg_subtrans lookups when
200 : : * determining visibility, but doesn't care about rows above its xmin to
201 : : * be removed.
202 : : *
203 : : * This likely should only be needed to determine whether pg_subtrans can
204 : : * be truncated. It currently includes the effects of replication slots,
205 : : * for historical reasons. But that could likely be changed.
206 : : */
207 : : TransactionId oldest_considered_running;
208 : :
209 : : /*
210 : : * Oldest xid for which deleted tuples need to be retained in shared
211 : : * tables.
212 : : *
213 : : * This includes the effects of replication slots. If that's not desired,
214 : : * look at shared_oldest_nonremovable_raw;
215 : : */
216 : : TransactionId shared_oldest_nonremovable;
217 : :
218 : : /*
219 : : * Oldest xid that may be necessary to retain in shared tables. This is
220 : : * the same as shared_oldest_nonremovable, except that is not affected by
221 : : * replication slot's catalog_xmin.
222 : : *
223 : : * This is mainly useful to be able to send the catalog_xmin to upstream
224 : : * streaming replication servers via hot_standby_feedback, so they can
225 : : * apply the limit only when accessing catalog tables.
226 : : */
227 : : TransactionId shared_oldest_nonremovable_raw;
228 : :
229 : : /*
230 : : * Oldest xid for which deleted tuples need to be retained in non-shared
231 : : * catalog tables.
232 : : */
233 : : TransactionId catalog_oldest_nonremovable;
234 : :
235 : : /*
236 : : * Oldest xid for which deleted tuples need to be retained in normal user
237 : : * defined tables.
238 : : */
239 : : TransactionId data_oldest_nonremovable;
240 : :
241 : : /*
242 : : * Oldest xid for which deleted tuples need to be retained in this
243 : : * session's temporary tables.
244 : : */
245 : : TransactionId temp_oldest_nonremovable;
246 : : } ComputeXidHorizonsResult;
247 : :
248 : : /*
249 : : * Return value for GlobalVisHorizonKindForRel().
250 : : */
251 : : typedef enum GlobalVisHorizonKind
252 : : {
253 : : VISHORIZON_SHARED,
254 : : VISHORIZON_CATALOG,
255 : : VISHORIZON_DATA,
256 : : VISHORIZON_TEMP,
257 : : } GlobalVisHorizonKind;
258 : :
259 : : /*
260 : : * Reason codes for KnownAssignedXidsCompress().
261 : : */
262 : : typedef enum KAXCompressReason
263 : : {
264 : : KAX_NO_SPACE, /* need to free up space at array end */
265 : : KAX_PRUNE, /* we just pruned old entries */
266 : : KAX_TRANSACTION_END, /* we just committed/removed some XIDs */
267 : : KAX_STARTUP_PROCESS_IDLE, /* startup process is about to sleep */
268 : : } KAXCompressReason;
269 : :
270 : :
271 : : static ProcArrayStruct *procArray;
272 : :
273 : : static PGPROC *allProcs;
274 : :
275 : : /*
276 : : * Cache to reduce overhead of repeated calls to TransactionIdIsInProgress()
277 : : */
278 : : static TransactionId cachedXidIsNotInProgress = InvalidTransactionId;
279 : :
280 : : /*
281 : : * Bookkeeping for tracking emulated transactions in recovery
282 : : */
283 : : static TransactionId *KnownAssignedXids;
284 : : static bool *KnownAssignedXidsValid;
285 : : static TransactionId latestObservedXid = InvalidTransactionId;
286 : :
287 : : /*
288 : : * If we're in STANDBY_SNAPSHOT_PENDING state, standbySnapshotPendingXmin is
289 : : * the highest xid that might still be running that we don't have in
290 : : * KnownAssignedXids.
291 : : */
292 : : static TransactionId standbySnapshotPendingXmin;
293 : :
294 : : /*
295 : : * State for visibility checks on different types of relations. See struct
296 : : * GlobalVisState for details. As shared, catalog, normal and temporary
297 : : * relations can have different horizons, one such state exists for each.
298 : : */
299 : : static GlobalVisState GlobalVisSharedRels;
300 : : static GlobalVisState GlobalVisCatalogRels;
301 : : static GlobalVisState GlobalVisDataRels;
302 : : static GlobalVisState GlobalVisTempRels;
303 : :
304 : : /*
305 : : * This backend's RecentXmin at the last time the accurate xmin horizon was
306 : : * recomputed, or InvalidTransactionId if it has not. Used to limit how many
307 : : * times accurate horizons are recomputed. See GlobalVisTestShouldUpdate().
308 : : */
309 : : static TransactionId ComputeXidHorizonsResultLastXmin;
310 : :
311 : : #ifdef XIDCACHE_DEBUG
312 : :
313 : : /* counters for XidCache measurement */
314 : : static long xc_by_recent_xmin = 0;
315 : : static long xc_by_known_xact = 0;
316 : : static long xc_by_my_xact = 0;
317 : : static long xc_by_latest_xid = 0;
318 : : static long xc_by_main_xid = 0;
319 : : static long xc_by_child_xid = 0;
320 : : static long xc_by_known_assigned = 0;
321 : : static long xc_no_overflow = 0;
322 : : static long xc_slow_answer = 0;
323 : :
324 : : #define xc_by_recent_xmin_inc() (xc_by_recent_xmin++)
325 : : #define xc_by_known_xact_inc() (xc_by_known_xact++)
326 : : #define xc_by_my_xact_inc() (xc_by_my_xact++)
327 : : #define xc_by_latest_xid_inc() (xc_by_latest_xid++)
328 : : #define xc_by_main_xid_inc() (xc_by_main_xid++)
329 : : #define xc_by_child_xid_inc() (xc_by_child_xid++)
330 : : #define xc_by_known_assigned_inc() (xc_by_known_assigned++)
331 : : #define xc_no_overflow_inc() (xc_no_overflow++)
332 : : #define xc_slow_answer_inc() (xc_slow_answer++)
333 : :
334 : : static void DisplayXidCache(void);
335 : : #else /* !XIDCACHE_DEBUG */
336 : :
337 : : #define xc_by_recent_xmin_inc() ((void) 0)
338 : : #define xc_by_known_xact_inc() ((void) 0)
339 : : #define xc_by_my_xact_inc() ((void) 0)
340 : : #define xc_by_latest_xid_inc() ((void) 0)
341 : : #define xc_by_main_xid_inc() ((void) 0)
342 : : #define xc_by_child_xid_inc() ((void) 0)
343 : : #define xc_by_known_assigned_inc() ((void) 0)
344 : : #define xc_no_overflow_inc() ((void) 0)
345 : : #define xc_slow_answer_inc() ((void) 0)
346 : : #endif /* XIDCACHE_DEBUG */
347 : :
348 : : /* Primitives for KnownAssignedXids array handling for standby */
349 : : static void KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock);
350 : : static void KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
351 : : bool exclusive_lock);
352 : : static bool KnownAssignedXidsSearch(TransactionId xid, bool remove);
353 : : static bool KnownAssignedXidExists(TransactionId xid);
354 : : static void KnownAssignedXidsRemove(TransactionId xid);
355 : : static void KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
356 : : TransactionId *subxids);
357 : : static void KnownAssignedXidsRemovePreceding(TransactionId removeXid);
358 : : static int KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax);
359 : : static int KnownAssignedXidsGetAndSetXmin(TransactionId *xarray,
360 : : TransactionId *xmin,
361 : : TransactionId xmax);
362 : : static TransactionId KnownAssignedXidsGetOldestXmin(void);
363 : : static void KnownAssignedXidsDisplay(int trace_level);
364 : : static void KnownAssignedXidsReset(void);
365 : : static inline void ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid);
366 : : static void ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid);
367 : : static void MaintainLatestCompletedXid(TransactionId latestXid);
368 : : static void MaintainLatestCompletedXidRecovery(TransactionId latestXid);
369 : :
370 : : static inline FullTransactionId FullXidRelativeTo(FullTransactionId rel,
371 : : TransactionId xid);
372 : : static void GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons);
373 : :
374 : : /*
375 : : * Report shared-memory space needed by ProcArrayShmemInit
376 : : */
377 : : Size
378 : 9 : ProcArrayShmemSize(void)
379 : : {
380 : 9 : Size size;
381 : :
382 : : /* Size of the ProcArray structure itself */
383 : : #define PROCARRAY_MAXPROCS (MaxBackends + max_prepared_xacts)
384 : :
385 : 9 : size = offsetof(ProcArrayStruct, pgprocnos);
386 : 9 : size = add_size(size, mul_size(sizeof(int), PROCARRAY_MAXPROCS));
387 : :
388 : : /*
389 : : * During Hot Standby processing we have a data structure called
390 : : * KnownAssignedXids, created in shared memory. Local data structures are
391 : : * also created in various backends during GetSnapshotData(),
392 : : * TransactionIdIsInProgress() and GetRunningTransactionData(). All of the
393 : : * main structures created in those functions must be identically sized,
394 : : * since we may at times copy the whole of the data structures around. We
395 : : * refer to this size as TOTAL_MAX_CACHED_SUBXIDS.
396 : : *
397 : : * Ideally we'd only create this structure if we were actually doing hot
398 : : * standby in the current run, but we don't know that yet at the time
399 : : * shared memory is being set up.
400 : : */
401 : : #define TOTAL_MAX_CACHED_SUBXIDS \
402 : : ((PGPROC_MAX_CACHED_SUBXIDS + 1) * PROCARRAY_MAXPROCS)
403 : :
404 [ - + ]: 9 : if (EnableHotStandby)
405 : : {
406 : 18 : size = add_size(size,
407 : 9 : mul_size(sizeof(TransactionId),
408 : 9 : TOTAL_MAX_CACHED_SUBXIDS));
409 : 18 : size = add_size(size,
410 : 9 : mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS));
411 : 9 : }
412 : :
413 : 18 : return size;
414 : 9 : }
415 : :
416 : : /*
417 : : * Initialize the shared PGPROC array during postmaster startup.
418 : : */
419 : : void
420 : 6 : ProcArrayShmemInit(void)
421 : : {
422 : 6 : bool found;
423 : :
424 : : /* Create or attach to the ProcArray shared structure */
425 : 6 : procArray = (ProcArrayStruct *)
426 : 6 : ShmemInitStruct("Proc Array",
427 : 6 : add_size(offsetof(ProcArrayStruct, pgprocnos),
428 : 6 : mul_size(sizeof(int),
429 : 6 : PROCARRAY_MAXPROCS)),
430 : : &found);
431 : :
432 [ - + ]: 6 : if (!found)
433 : : {
434 : : /*
435 : : * We're the first - initialize.
436 : : */
437 : 6 : procArray->numProcs = 0;
438 : 6 : procArray->maxProcs = PROCARRAY_MAXPROCS;
439 : 6 : procArray->maxKnownAssignedXids = TOTAL_MAX_CACHED_SUBXIDS;
440 : 6 : procArray->numKnownAssignedXids = 0;
441 : 6 : procArray->tailKnownAssignedXids = 0;
442 : 6 : procArray->headKnownAssignedXids = 0;
443 : 6 : procArray->lastOverflowedXid = InvalidTransactionId;
444 : 6 : procArray->replication_slot_xmin = InvalidTransactionId;
445 : 6 : procArray->replication_slot_catalog_xmin = InvalidTransactionId;
446 : 6 : TransamVariables->xactCompletionCount = 1;
447 : 6 : }
448 : :
449 : 6 : allProcs = ProcGlobal->allProcs;
450 : :
451 : : /* Create or attach to the KnownAssignedXids arrays too, if needed */
452 [ - + ]: 6 : if (EnableHotStandby)
453 : : {
454 : 6 : KnownAssignedXids = (TransactionId *)
455 : 6 : ShmemInitStruct("KnownAssignedXids",
456 : 6 : mul_size(sizeof(TransactionId),
457 : 6 : TOTAL_MAX_CACHED_SUBXIDS),
458 : : &found);
459 : 6 : KnownAssignedXidsValid = (bool *)
460 : 6 : ShmemInitStruct("KnownAssignedXidsValid",
461 : 6 : mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS),
462 : : &found);
463 : 6 : }
464 : 6 : }
465 : :
466 : : /*
467 : : * Add the specified PGPROC to the shared array.
468 : : */
469 : : void
470 : 798 : ProcArrayAdd(PGPROC *proc)
471 : : {
472 : 798 : int pgprocno = GetNumberFromPGProc(proc);
473 : 798 : ProcArrayStruct *arrayP = procArray;
474 : 798 : int index;
475 : 798 : int movecount;
476 : :
477 : : /* See ProcGlobal comment explaining why both locks are held */
478 : 798 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
479 : 798 : LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
480 : :
481 [ + - ]: 798 : if (arrayP->numProcs >= arrayP->maxProcs)
482 : : {
483 : : /*
484 : : * Oops, no room. (This really shouldn't happen, since there is a
485 : : * fixed supply of PGPROC structs too, and so we should have failed
486 : : * earlier.)
487 : : */
488 [ # # # # ]: 0 : ereport(FATAL,
489 : : (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
490 : : errmsg("sorry, too many clients already")));
491 : 0 : }
492 : :
493 : : /*
494 : : * Keep the procs array sorted by (PGPROC *) so that we can utilize
495 : : * locality of references much better. This is useful while traversing the
496 : : * ProcArray because there is an increased likelihood of finding the next
497 : : * PGPROC structure in the cache.
498 : : *
499 : : * Since the occurrence of adding/removing a proc is much lower than the
500 : : * access to the ProcArray itself, the overhead should be marginal
501 : : */
502 [ + + ]: 5040 : for (index = 0; index < arrayP->numProcs; index++)
503 : : {
504 : 4723 : int this_procno = arrayP->pgprocnos[index];
505 : :
506 [ + - ]: 4723 : Assert(this_procno >= 0 && this_procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
507 [ + - ]: 4723 : Assert(allProcs[this_procno].pgxactoff == index);
508 : :
509 : : /* If we have found our right position in the array, break */
510 [ + + ]: 4723 : if (this_procno > pgprocno)
511 : 481 : break;
512 [ - + + ]: 4723 : }
513 : :
514 : 798 : movecount = arrayP->numProcs - index;
515 : 798 : memmove(&arrayP->pgprocnos[index + 1],
516 : : &arrayP->pgprocnos[index],
517 : : movecount * sizeof(*arrayP->pgprocnos));
518 : 798 : memmove(&ProcGlobal->xids[index + 1],
519 : : &ProcGlobal->xids[index],
520 : : movecount * sizeof(*ProcGlobal->xids));
521 : 798 : memmove(&ProcGlobal->subxidStates[index + 1],
522 : : &ProcGlobal->subxidStates[index],
523 : : movecount * sizeof(*ProcGlobal->subxidStates));
524 : 798 : memmove(&ProcGlobal->statusFlags[index + 1],
525 : : &ProcGlobal->statusFlags[index],
526 : : movecount * sizeof(*ProcGlobal->statusFlags));
527 : :
528 : 798 : arrayP->pgprocnos[index] = GetNumberFromPGProc(proc);
529 : 798 : proc->pgxactoff = index;
530 : 798 : ProcGlobal->xids[index] = proc->xid;
531 : 798 : ProcGlobal->subxidStates[index] = proc->subxidStatus;
532 : 798 : ProcGlobal->statusFlags[index] = proc->statusFlags;
533 : :
534 : 798 : arrayP->numProcs++;
535 : :
536 : : /* adjust pgxactoff for all following PGPROCs */
537 : 798 : index++;
538 [ + + ]: 1979 : for (; index < arrayP->numProcs; index++)
539 : : {
540 : 1181 : int procno = arrayP->pgprocnos[index];
541 : :
542 [ + - ]: 1181 : Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
543 [ - + ]: 1181 : Assert(allProcs[procno].pgxactoff == index - 1);
544 : :
545 : 1181 : allProcs[procno].pgxactoff = index;
546 : 1181 : }
547 : :
548 : : /*
549 : : * Release in reversed acquisition order, to reduce frequency of having to
550 : : * wait for XidGenLock while holding ProcArrayLock.
551 : : */
552 : 798 : LWLockRelease(XidGenLock);
553 : 798 : LWLockRelease(ProcArrayLock);
554 : 798 : }
555 : :
556 : : /*
557 : : * Remove the specified PGPROC from the shared array.
558 : : *
559 : : * When latestXid is a valid XID, we are removing a live 2PC gxact from the
560 : : * array, and thus causing it to appear as "not running" anymore. In this
561 : : * case we must advance latestCompletedXid. (This is essentially the same
562 : : * as ProcArrayEndTransaction followed by removal of the PGPROC, but we take
563 : : * the ProcArrayLock only once, and don't damage the content of the PGPROC;
564 : : * twophase.c depends on the latter.)
565 : : */
566 : : void
567 : 798 : ProcArrayRemove(PGPROC *proc, TransactionId latestXid)
568 : : {
569 : 798 : ProcArrayStruct *arrayP = procArray;
570 : 798 : int myoff;
571 : 798 : int movecount;
572 : :
573 : : #ifdef XIDCACHE_DEBUG
574 : : /* dump stats at backend shutdown, but not prepared-xact end */
575 : : if (proc->pid != 0)
576 : : DisplayXidCache();
577 : : #endif
578 : :
579 : : /* See ProcGlobal comment explaining why both locks are held */
580 : 798 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
581 : 798 : LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
582 : :
583 : 798 : myoff = proc->pgxactoff;
584 : :
585 [ + - ]: 798 : Assert(myoff >= 0 && myoff < arrayP->numProcs);
586 [ + - ]: 798 : Assert(ProcGlobal->allProcs[arrayP->pgprocnos[myoff]].pgxactoff == myoff);
587 : :
588 [ - + ]: 798 : if (TransactionIdIsValid(latestXid))
589 : : {
590 [ # # ]: 0 : Assert(TransactionIdIsValid(ProcGlobal->xids[myoff]));
591 : :
592 : : /* Advance global latestCompletedXid while holding the lock */
593 : 0 : MaintainLatestCompletedXid(latestXid);
594 : :
595 : : /* Same with xactCompletionCount */
596 : 0 : TransamVariables->xactCompletionCount++;
597 : :
598 : 0 : ProcGlobal->xids[myoff] = InvalidTransactionId;
599 : 0 : ProcGlobal->subxidStates[myoff].overflowed = false;
600 : 0 : ProcGlobal->subxidStates[myoff].count = 0;
601 : 0 : }
602 : : else
603 : : {
604 : : /* Shouldn't be trying to remove a live transaction here */
605 [ + - ]: 798 : Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
606 : : }
607 : :
608 [ + - ]: 798 : Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
609 [ + - ]: 798 : Assert(ProcGlobal->subxidStates[myoff].count == 0);
610 [ + - ]: 798 : Assert(ProcGlobal->subxidStates[myoff].overflowed == false);
611 : :
612 : 798 : ProcGlobal->statusFlags[myoff] = 0;
613 : :
614 : : /* Keep the PGPROC array sorted. See notes above */
615 : 798 : movecount = arrayP->numProcs - myoff - 1;
616 : 798 : memmove(&arrayP->pgprocnos[myoff],
617 : : &arrayP->pgprocnos[myoff + 1],
618 : : movecount * sizeof(*arrayP->pgprocnos));
619 : 798 : memmove(&ProcGlobal->xids[myoff],
620 : : &ProcGlobal->xids[myoff + 1],
621 : : movecount * sizeof(*ProcGlobal->xids));
622 : 798 : memmove(&ProcGlobal->subxidStates[myoff],
623 : : &ProcGlobal->subxidStates[myoff + 1],
624 : : movecount * sizeof(*ProcGlobal->subxidStates));
625 : 798 : memmove(&ProcGlobal->statusFlags[myoff],
626 : : &ProcGlobal->statusFlags[myoff + 1],
627 : : movecount * sizeof(*ProcGlobal->statusFlags));
628 : :
629 : 798 : arrayP->pgprocnos[arrayP->numProcs - 1] = -1; /* for debugging */
630 : 798 : arrayP->numProcs--;
631 : :
632 : : /*
633 : : * Adjust pgxactoff of following procs for removed PGPROC (note that
634 : : * numProcs already has been decremented).
635 : : */
636 [ + + ]: 2700 : for (int index = myoff; index < arrayP->numProcs; index++)
637 : : {
638 : 1902 : int procno = arrayP->pgprocnos[index];
639 : :
640 [ + - ]: 1902 : Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
641 [ - + ]: 1902 : Assert(allProcs[procno].pgxactoff - 1 == index);
642 : :
643 : 1902 : allProcs[procno].pgxactoff = index;
644 : 1902 : }
645 : :
646 : : /*
647 : : * Release in reversed acquisition order, to reduce frequency of having to
648 : : * wait for XidGenLock while holding ProcArrayLock.
649 : : */
650 : 798 : LWLockRelease(XidGenLock);
651 : 798 : LWLockRelease(ProcArrayLock);
652 : 798 : }
653 : :
654 : :
655 : : /*
656 : : * ProcArrayEndTransaction -- mark a transaction as no longer running
657 : : *
658 : : * This is used interchangeably for commit and abort cases. The transaction
659 : : * commit/abort must already be reported to WAL and pg_xact.
660 : : *
661 : : * proc is currently always MyProc, but we pass it explicitly for flexibility.
662 : : * latestXid is the latest Xid among the transaction's main XID and
663 : : * subtransactions, or InvalidTransactionId if it has no XID. (We must ask
664 : : * the caller to pass latestXid, instead of computing it from the PGPROC's
665 : : * contents, because the subxid information in the PGPROC might be
666 : : * incomplete.)
667 : : */
668 : : void
669 : 57914 : ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid)
670 : : {
671 [ + + ]: 57914 : if (TransactionIdIsValid(latestXid))
672 : : {
673 : : /*
674 : : * We must lock ProcArrayLock while clearing our advertised XID, so
675 : : * that we do not exit the set of "running" transactions while someone
676 : : * else is taking a snapshot. See discussion in
677 : : * src/backend/access/transam/README.
678 : : */
679 [ + - ]: 21770 : Assert(TransactionIdIsValid(proc->xid));
680 : :
681 : : /*
682 : : * If we can immediately acquire ProcArrayLock, we clear our own XID
683 : : * and release the lock. If not, use group XID clearing to improve
684 : : * efficiency.
685 : : */
686 [ + + ]: 21770 : if (LWLockConditionalAcquire(ProcArrayLock, LW_EXCLUSIVE))
687 : : {
688 : 21733 : ProcArrayEndTransactionInternal(proc, latestXid);
689 : 21733 : LWLockRelease(ProcArrayLock);
690 : 21733 : }
691 : : else
692 : 37 : ProcArrayGroupClearXid(proc, latestXid);
693 : 21770 : }
694 : : else
695 : : {
696 : : /*
697 : : * If we have no XID, we don't need to lock, since we won't affect
698 : : * anyone else's calculation of a snapshot. We might change their
699 : : * estimate of global xmin, but that's OK.
700 : : */
701 [ + - ]: 36144 : Assert(!TransactionIdIsValid(proc->xid));
702 [ + - ]: 36144 : Assert(proc->subxidStatus.count == 0);
703 [ + - ]: 36144 : Assert(!proc->subxidStatus.overflowed);
704 : :
705 : 36144 : proc->vxid.lxid = InvalidLocalTransactionId;
706 : 36144 : proc->xmin = InvalidTransactionId;
707 : :
708 : : /* be sure this is cleared in abort */
709 : 36144 : proc->delayChkptFlags = 0;
710 : :
711 : 36144 : proc->recoveryConflictPending = false;
712 : :
713 : : /* must be cleared with xid/xmin: */
714 : : /* avoid unnecessarily dirtying shared cachelines */
715 [ + + ]: 36144 : if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
716 : : {
717 [ + - ]: 749 : Assert(!LWLockHeldByMe(ProcArrayLock));
718 : 749 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
719 [ + - ]: 749 : Assert(proc->statusFlags == ProcGlobal->statusFlags[proc->pgxactoff]);
720 : 749 : proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
721 : 749 : ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
722 : 749 : LWLockRelease(ProcArrayLock);
723 : 749 : }
724 : : }
725 : 57914 : }
726 : :
727 : : /*
728 : : * Mark a write transaction as no longer running.
729 : : *
730 : : * We don't do any locking here; caller must handle that.
731 : : */
732 : : static inline void
733 : 21770 : ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid)
734 : : {
735 : 21770 : int pgxactoff = proc->pgxactoff;
736 : :
737 : : /*
738 : : * Note: we need exclusive lock here because we're going to change other
739 : : * processes' PGPROC entries.
740 : : */
741 [ + - ]: 21770 : Assert(LWLockHeldByMeInMode(ProcArrayLock, LW_EXCLUSIVE));
742 [ + - ]: 21770 : Assert(TransactionIdIsValid(ProcGlobal->xids[pgxactoff]));
743 [ + - ]: 21770 : Assert(ProcGlobal->xids[pgxactoff] == proc->xid);
744 : :
745 : 21770 : ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
746 : 21770 : proc->xid = InvalidTransactionId;
747 : 21770 : proc->vxid.lxid = InvalidLocalTransactionId;
748 : 21770 : proc->xmin = InvalidTransactionId;
749 : :
750 : : /* be sure this is cleared in abort */
751 : 21770 : proc->delayChkptFlags = 0;
752 : :
753 : 21770 : proc->recoveryConflictPending = false;
754 : :
755 : : /* must be cleared with xid/xmin: */
756 : : /* avoid unnecessarily dirtying shared cachelines */
757 [ + + ]: 21770 : if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
758 : : {
759 : 87 : proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
760 : 87 : ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
761 : 87 : }
762 : :
763 : : /* Clear the subtransaction-XID cache too while holding the lock */
764 [ + - ]: 21770 : Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
765 : : ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
766 [ + + - + ]: 21770 : if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
767 : : {
768 : 29 : ProcGlobal->subxidStates[pgxactoff].count = 0;
769 : 29 : ProcGlobal->subxidStates[pgxactoff].overflowed = false;
770 : 29 : proc->subxidStatus.count = 0;
771 : 29 : proc->subxidStatus.overflowed = false;
772 : 29 : }
773 : :
774 : : /* Also advance global latestCompletedXid while holding the lock */
775 : 21770 : MaintainLatestCompletedXid(latestXid);
776 : :
777 : : /* Same with xactCompletionCount */
778 : 21770 : TransamVariables->xactCompletionCount++;
779 : 21770 : }
780 : :
781 : : /*
782 : : * ProcArrayGroupClearXid -- group XID clearing
783 : : *
784 : : * When we cannot immediately acquire ProcArrayLock in exclusive mode at
785 : : * commit time, add ourselves to a list of processes that need their XIDs
786 : : * cleared. The first process to add itself to the list will acquire
787 : : * ProcArrayLock in exclusive mode and perform ProcArrayEndTransactionInternal
788 : : * on behalf of all group members. This avoids a great deal of contention
789 : : * around ProcArrayLock when many processes are trying to commit at once,
790 : : * since the lock need not be repeatedly handed off from one committing
791 : : * process to the next.
792 : : */
793 : : static void
794 : 37 : ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
795 : : {
796 : 37 : int pgprocno = GetNumberFromPGProc(proc);
797 : 37 : PROC_HDR *procglobal = ProcGlobal;
798 : 37 : uint32 nextidx;
799 : 37 : uint32 wakeidx;
800 : :
801 : : /* We should definitely have an XID to clear. */
802 [ + - ]: 37 : Assert(TransactionIdIsValid(proc->xid));
803 : :
804 : : /* Add ourselves to the list of processes needing a group XID clear. */
805 : 37 : proc->procArrayGroupMember = true;
806 : 37 : proc->procArrayGroupMemberXid = latestXid;
807 : 37 : nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
808 : 37 : while (true)
809 : : {
810 : 37 : pg_atomic_write_u32(&proc->procArrayGroupNext, nextidx);
811 : :
812 [ - + - + ]: 74 : if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
813 : : &nextidx,
814 : 37 : (uint32) pgprocno))
815 : 37 : break;
816 : : }
817 : :
818 : : /*
819 : : * If the list was not empty, the leader will clear our XID. It is
820 : : * impossible to have followers without a leader because the first process
821 : : * that has added itself to the list will always have nextidx as
822 : : * INVALID_PROC_NUMBER.
823 : : */
824 [ + + ]: 37 : if (nextidx != INVALID_PROC_NUMBER)
825 : : {
826 : 1 : int extraWaits = 0;
827 : :
828 : : /* Sleep until the leader clears our XID. */
829 : 1 : pgstat_report_wait_start(WAIT_EVENT_PROCARRAY_GROUP_UPDATE);
830 : 1 : for (;;)
831 : : {
832 : : /* acts as a read barrier */
833 : 1 : PGSemaphoreLock(proc->sem);
834 [ - + ]: 1 : if (!proc->procArrayGroupMember)
835 : 1 : break;
836 : 0 : extraWaits++;
837 : : }
838 : 1 : pgstat_report_wait_end();
839 : :
840 [ + - ]: 1 : Assert(pg_atomic_read_u32(&proc->procArrayGroupNext) == INVALID_PROC_NUMBER);
841 : :
842 : : /* Fix semaphore count for any absorbed wakeups */
843 [ - + ]: 1 : while (extraWaits-- > 0)
844 : 0 : PGSemaphoreUnlock(proc->sem);
845 : : return;
846 : 1 : }
847 : :
848 : : /* We are the leader. Acquire the lock on behalf of everyone. */
849 : 36 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
850 : :
851 : : /*
852 : : * Now that we've got the lock, clear the list of processes waiting for
853 : : * group XID clearing, saving a pointer to the head of the list. Trying
854 : : * to pop elements one at a time could lead to an ABA problem.
855 : : */
856 : 36 : nextidx = pg_atomic_exchange_u32(&procglobal->procArrayGroupFirst,
857 : : INVALID_PROC_NUMBER);
858 : :
859 : : /* Remember head of list so we can perform wakeups after dropping lock. */
860 : 36 : wakeidx = nextidx;
861 : :
862 : : /* Walk the list and clear all XIDs. */
863 [ + + ]: 73 : while (nextidx != INVALID_PROC_NUMBER)
864 : : {
865 : 37 : PGPROC *nextproc = &allProcs[nextidx];
866 : :
867 : 37 : ProcArrayEndTransactionInternal(nextproc, nextproc->procArrayGroupMemberXid);
868 : :
869 : : /* Move to next proc in list. */
870 : 37 : nextidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
871 : 37 : }
872 : :
873 : : /* We're done with the lock now. */
874 : 36 : LWLockRelease(ProcArrayLock);
875 : :
876 : : /*
877 : : * Now that we've released the lock, go back and wake everybody up. We
878 : : * don't do this under the lock so as to keep lock hold times to a
879 : : * minimum. The system calls we need to perform to wake other processes
880 : : * up are probably much slower than the simple memory writes we did while
881 : : * holding the lock.
882 : : */
883 [ + + ]: 73 : while (wakeidx != INVALID_PROC_NUMBER)
884 : : {
885 : 37 : PGPROC *nextproc = &allProcs[wakeidx];
886 : :
887 : 37 : wakeidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
888 : 37 : pg_atomic_write_u32(&nextproc->procArrayGroupNext, INVALID_PROC_NUMBER);
889 : :
890 : : /* ensure all previous writes are visible before follower continues. */
891 : 37 : pg_write_barrier();
892 : :
893 : 37 : nextproc->procArrayGroupMember = false;
894 : :
895 [ + + ]: 37 : if (nextproc != MyProc)
896 : 1 : PGSemaphoreUnlock(nextproc->sem);
897 : 37 : }
898 [ - + ]: 37 : }
899 : :
900 : : /*
901 : : * ProcArrayClearTransaction -- clear the transaction fields
902 : : *
903 : : * This is used after successfully preparing a 2-phase transaction. We are
904 : : * not actually reporting the transaction's XID as no longer running --- it
905 : : * will still appear as running because the 2PC's gxact is in the ProcArray
906 : : * too. We just have to clear out our own PGPROC.
907 : : */
908 : : void
909 : 0 : ProcArrayClearTransaction(PGPROC *proc)
910 : : {
911 : 0 : int pgxactoff;
912 : :
913 : : /*
914 : : * Currently we need to lock ProcArrayLock exclusively here, as we
915 : : * increment xactCompletionCount below. We also need it at least in shared
916 : : * mode for pgproc->pgxactoff to stay the same below.
917 : : *
918 : : * We could however, as this action does not actually change anyone's view
919 : : * of the set of running XIDs (our entry is duplicate with the gxact that
920 : : * has already been inserted into the ProcArray), lower the lock level to
921 : : * shared if we were to make xactCompletionCount an atomic variable. But
922 : : * that doesn't seem worth it currently, as a 2PC commit is heavyweight
923 : : * enough for this not to be the bottleneck. If it ever becomes a
924 : : * bottleneck it may also be worth considering to combine this with the
925 : : * subsequent ProcArrayRemove()
926 : : */
927 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
928 : :
929 : 0 : pgxactoff = proc->pgxactoff;
930 : :
931 : 0 : ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
932 : 0 : proc->xid = InvalidTransactionId;
933 : :
934 : 0 : proc->vxid.lxid = InvalidLocalTransactionId;
935 : 0 : proc->xmin = InvalidTransactionId;
936 : 0 : proc->recoveryConflictPending = false;
937 : :
938 [ # # ]: 0 : Assert(!(proc->statusFlags & PROC_VACUUM_STATE_MASK));
939 [ # # ]: 0 : Assert(!proc->delayChkptFlags);
940 : :
941 : : /*
942 : : * Need to increment completion count even though transaction hasn't
943 : : * really committed yet. The reason for that is that GetSnapshotData()
944 : : * omits the xid of the current transaction, thus without the increment we
945 : : * otherwise could end up reusing the snapshot later. Which would be bad,
946 : : * because it might not count the prepared transaction as running.
947 : : */
948 : 0 : TransamVariables->xactCompletionCount++;
949 : :
950 : : /* Clear the subtransaction-XID cache too */
951 [ # # ]: 0 : Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
952 : : ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
953 [ # # # # ]: 0 : if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
954 : : {
955 : 0 : ProcGlobal->subxidStates[pgxactoff].count = 0;
956 : 0 : ProcGlobal->subxidStates[pgxactoff].overflowed = false;
957 : 0 : proc->subxidStatus.count = 0;
958 : 0 : proc->subxidStatus.overflowed = false;
959 : 0 : }
960 : :
961 : 0 : LWLockRelease(ProcArrayLock);
962 : 0 : }
963 : :
964 : : /*
965 : : * Update TransamVariables->latestCompletedXid to point to latestXid if
966 : : * currently older.
967 : : */
968 : : static void
969 : 21951 : MaintainLatestCompletedXid(TransactionId latestXid)
970 : : {
971 : 21951 : FullTransactionId cur_latest = TransamVariables->latestCompletedXid;
972 : :
973 [ + - ]: 21951 : Assert(FullTransactionIdIsValid(cur_latest));
974 [ + - ]: 21951 : Assert(!RecoveryInProgress());
975 [ + - ]: 21951 : Assert(LWLockHeldByMe(ProcArrayLock));
976 : :
977 [ + + ]: 21951 : if (TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
978 : : {
979 : 18208 : TransamVariables->latestCompletedXid =
980 : 18208 : FullXidRelativeTo(cur_latest, latestXid);
981 : 18208 : }
982 : :
983 [ + + + - ]: 21951 : Assert(IsBootstrapProcessingMode() ||
984 : : FullTransactionIdIsNormal(TransamVariables->latestCompletedXid));
985 : 21951 : }
986 : :
987 : : /*
988 : : * Same as MaintainLatestCompletedXid, except for use during WAL replay.
989 : : */
990 : : static void
991 : 0 : MaintainLatestCompletedXidRecovery(TransactionId latestXid)
992 : : {
993 : 0 : FullTransactionId cur_latest = TransamVariables->latestCompletedXid;
994 : 0 : FullTransactionId rel;
995 : :
996 [ # # # # ]: 0 : Assert(AmStartupProcess() || !IsUnderPostmaster);
997 [ # # ]: 0 : Assert(LWLockHeldByMe(ProcArrayLock));
998 : :
999 : : /*
1000 : : * Need a FullTransactionId to compare latestXid with. Can't rely on
1001 : : * latestCompletedXid to be initialized in recovery. But in recovery it's
1002 : : * safe to access nextXid without a lock for the startup process.
1003 : : */
1004 : 0 : rel = TransamVariables->nextXid;
1005 [ # # ]: 0 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
1006 : :
1007 [ # # # # ]: 0 : if (!FullTransactionIdIsValid(cur_latest) ||
1008 : 0 : TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
1009 : : {
1010 : 0 : TransamVariables->latestCompletedXid =
1011 : 0 : FullXidRelativeTo(rel, latestXid);
1012 : 0 : }
1013 : :
1014 [ # # ]: 0 : Assert(FullTransactionIdIsNormal(TransamVariables->latestCompletedXid));
1015 : 0 : }
1016 : :
1017 : : /*
1018 : : * ProcArrayInitRecovery -- initialize recovery xid mgmt environment
1019 : : *
1020 : : * Remember up to where the startup process initialized the CLOG and subtrans
1021 : : * so we can ensure it's initialized gaplessly up to the point where necessary
1022 : : * while in recovery.
1023 : : */
1024 : : void
1025 : 0 : ProcArrayInitRecovery(TransactionId initializedUptoXID)
1026 : : {
1027 [ # # ]: 0 : Assert(standbyState == STANDBY_INITIALIZED);
1028 [ # # ]: 0 : Assert(TransactionIdIsNormal(initializedUptoXID));
1029 : :
1030 : : /*
1031 : : * we set latestObservedXid to the xid SUBTRANS has been initialized up
1032 : : * to, so we can extend it from that point onwards in
1033 : : * RecordKnownAssignedTransactionIds, and when we get consistent in
1034 : : * ProcArrayApplyRecoveryInfo().
1035 : : */
1036 : 0 : latestObservedXid = initializedUptoXID;
1037 [ # # ]: 0 : TransactionIdRetreat(latestObservedXid);
1038 : 0 : }
1039 : :
1040 : : /*
1041 : : * ProcArrayApplyRecoveryInfo -- apply recovery info about xids
1042 : : *
1043 : : * Takes us through 3 states: Initialized, Pending and Ready.
1044 : : * Normal case is to go all the way to Ready straight away, though there
1045 : : * are atypical cases where we need to take it in steps.
1046 : : *
1047 : : * Use the data about running transactions on the primary to create the initial
1048 : : * state of KnownAssignedXids. We also use these records to regularly prune
1049 : : * KnownAssignedXids because we know it is possible that some transactions
1050 : : * with FATAL errors fail to write abort records, which could cause eventual
1051 : : * overflow.
1052 : : *
1053 : : * See comments for LogStandbySnapshot().
1054 : : */
1055 : : void
1056 : 0 : ProcArrayApplyRecoveryInfo(RunningTransactions running)
1057 : : {
1058 : 0 : TransactionId *xids;
1059 : 0 : TransactionId advanceNextXid;
1060 : 0 : int nxids;
1061 : 0 : int i;
1062 : :
1063 [ # # ]: 0 : Assert(standbyState >= STANDBY_INITIALIZED);
1064 [ # # ]: 0 : Assert(TransactionIdIsValid(running->nextXid));
1065 [ # # ]: 0 : Assert(TransactionIdIsValid(running->oldestRunningXid));
1066 [ # # ]: 0 : Assert(TransactionIdIsNormal(running->latestCompletedXid));
1067 : :
1068 : : /*
1069 : : * Remove stale transactions, if any.
1070 : : */
1071 : 0 : ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
1072 : :
1073 : : /*
1074 : : * Adjust TransamVariables->nextXid before StandbyReleaseOldLocks(),
1075 : : * because we will need it up to date for accessing two-phase transactions
1076 : : * in StandbyReleaseOldLocks().
1077 : : */
1078 : 0 : advanceNextXid = running->nextXid;
1079 [ # # ]: 0 : TransactionIdRetreat(advanceNextXid);
1080 : 0 : AdvanceNextFullTransactionIdPastXid(advanceNextXid);
1081 [ # # ]: 0 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
1082 : :
1083 : : /*
1084 : : * Remove stale locks, if any.
1085 : : */
1086 : 0 : StandbyReleaseOldLocks(running->oldestRunningXid);
1087 : :
1088 : : /*
1089 : : * If our snapshot is already valid, nothing else to do...
1090 : : */
1091 [ # # ]: 0 : if (standbyState == STANDBY_SNAPSHOT_READY)
1092 : 0 : return;
1093 : :
1094 : : /*
1095 : : * If our initial RunningTransactionsData had an overflowed snapshot then
1096 : : * we knew we were missing some subxids from our snapshot. If we continue
1097 : : * to see overflowed snapshots then we might never be able to start up, so
1098 : : * we make another test to see if our snapshot is now valid. We know that
1099 : : * the missing subxids are equal to or earlier than nextXid. After we
1100 : : * initialise we continue to apply changes during recovery, so once the
1101 : : * oldestRunningXid is later than the nextXid from the initial snapshot we
1102 : : * know that we no longer have missing information and can mark the
1103 : : * snapshot as valid.
1104 : : */
1105 [ # # ]: 0 : if (standbyState == STANDBY_SNAPSHOT_PENDING)
1106 : : {
1107 : : /*
1108 : : * If the snapshot isn't overflowed or if its empty we can reset our
1109 : : * pending state and use this snapshot instead.
1110 : : */
1111 [ # # # # ]: 0 : if (running->subxid_status != SUBXIDS_MISSING || running->xcnt == 0)
1112 : : {
1113 : : /*
1114 : : * If we have already collected known assigned xids, we need to
1115 : : * throw them away before we apply the recovery snapshot.
1116 : : */
1117 : 0 : KnownAssignedXidsReset();
1118 : 0 : standbyState = STANDBY_INITIALIZED;
1119 : 0 : }
1120 : : else
1121 : : {
1122 [ # # # # ]: 0 : if (TransactionIdPrecedes(standbySnapshotPendingXmin,
1123 : 0 : running->oldestRunningXid))
1124 : : {
1125 : 0 : standbyState = STANDBY_SNAPSHOT_READY;
1126 [ # # # # ]: 0 : elog(DEBUG1,
1127 : : "recovery snapshots are now enabled");
1128 : 0 : }
1129 : : else
1130 [ # # # # ]: 0 : elog(DEBUG1,
1131 : : "recovery snapshot waiting for non-overflowed snapshot or "
1132 : : "until oldest active xid on standby is at least %u (now %u)",
1133 : : standbySnapshotPendingXmin,
1134 : : running->oldestRunningXid);
1135 : 0 : return;
1136 : : }
1137 : 0 : }
1138 : :
1139 [ # # ]: 0 : Assert(standbyState == STANDBY_INITIALIZED);
1140 : :
1141 : : /*
1142 : : * NB: this can be reached at least twice, so make sure new code can deal
1143 : : * with that.
1144 : : */
1145 : :
1146 : : /*
1147 : : * Nobody else is running yet, but take locks anyhow
1148 : : */
1149 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1150 : :
1151 : : /*
1152 : : * KnownAssignedXids is sorted so we cannot just add the xids, we have to
1153 : : * sort them first.
1154 : : *
1155 : : * Some of the new xids are top-level xids and some are subtransactions.
1156 : : * We don't call SubTransSetParent because it doesn't matter yet. If we
1157 : : * aren't overflowed then all xids will fit in snapshot and so we don't
1158 : : * need subtrans. If we later overflow, an xid assignment record will add
1159 : : * xids to subtrans. If RunningTransactionsData is overflowed then we
1160 : : * don't have enough information to correctly update subtrans anyway.
1161 : : */
1162 : :
1163 : : /*
1164 : : * Allocate a temporary array to avoid modifying the array passed as
1165 : : * argument.
1166 : : */
1167 : 0 : xids = palloc_array(TransactionId, running->xcnt + running->subxcnt);
1168 : :
1169 : : /*
1170 : : * Add to the temp array any xids which have not already completed.
1171 : : */
1172 : 0 : nxids = 0;
1173 [ # # ]: 0 : for (i = 0; i < running->xcnt + running->subxcnt; i++)
1174 : : {
1175 : 0 : TransactionId xid = running->xids[i];
1176 : :
1177 : : /*
1178 : : * The running-xacts snapshot can contain xids that were still visible
1179 : : * in the procarray when the snapshot was taken, but were already
1180 : : * WAL-logged as completed. They're not running anymore, so ignore
1181 : : * them.
1182 : : */
1183 [ # # # # ]: 0 : if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
1184 : 0 : continue;
1185 : :
1186 : 0 : xids[nxids++] = xid;
1187 [ # # ]: 0 : }
1188 : :
1189 [ # # ]: 0 : if (nxids > 0)
1190 : : {
1191 [ # # ]: 0 : if (procArray->numKnownAssignedXids != 0)
1192 : : {
1193 : 0 : LWLockRelease(ProcArrayLock);
1194 [ # # # # ]: 0 : elog(ERROR, "KnownAssignedXids is not empty");
1195 : 0 : }
1196 : :
1197 : : /*
1198 : : * Sort the array so that we can add them safely into
1199 : : * KnownAssignedXids.
1200 : : *
1201 : : * We have to sort them logically, because in KnownAssignedXidsAdd we
1202 : : * call TransactionIdFollowsOrEquals and so on. But we know these XIDs
1203 : : * come from RUNNING_XACTS, which means there are only normal XIDs
1204 : : * from the same epoch, so this is safe.
1205 : : */
1206 : 0 : qsort(xids, nxids, sizeof(TransactionId), xidLogicalComparator);
1207 : :
1208 : : /*
1209 : : * Add the sorted snapshot into KnownAssignedXids. The running-xacts
1210 : : * snapshot may include duplicated xids because of prepared
1211 : : * transactions, so ignore them.
1212 : : */
1213 [ # # ]: 0 : for (i = 0; i < nxids; i++)
1214 : : {
1215 [ # # # # ]: 0 : if (i > 0 && TransactionIdEquals(xids[i - 1], xids[i]))
1216 : : {
1217 [ # # # # ]: 0 : elog(DEBUG1,
1218 : : "found duplicated transaction %u for KnownAssignedXids insertion",
1219 : : xids[i]);
1220 : 0 : continue;
1221 : : }
1222 : 0 : KnownAssignedXidsAdd(xids[i], xids[i], true);
1223 : 0 : }
1224 : :
1225 : 0 : KnownAssignedXidsDisplay(DEBUG3);
1226 : 0 : }
1227 : :
1228 : 0 : pfree(xids);
1229 : :
1230 : : /*
1231 : : * latestObservedXid is at least set to the point where SUBTRANS was
1232 : : * started up to (cf. ProcArrayInitRecovery()) or to the biggest xid
1233 : : * RecordKnownAssignedTransactionIds() was called for. Initialize
1234 : : * subtrans from thereon, up to nextXid - 1.
1235 : : *
1236 : : * We need to duplicate parts of RecordKnownAssignedTransactionId() here,
1237 : : * because we've just added xids to the known assigned xids machinery that
1238 : : * haven't gone through RecordKnownAssignedTransactionId().
1239 : : */
1240 [ # # ]: 0 : Assert(TransactionIdIsNormal(latestObservedXid));
1241 [ # # ]: 0 : TransactionIdAdvance(latestObservedXid);
1242 [ # # ]: 0 : while (TransactionIdPrecedes(latestObservedXid, running->nextXid))
1243 : : {
1244 : 0 : ExtendSUBTRANS(latestObservedXid);
1245 [ # # ]: 0 : TransactionIdAdvance(latestObservedXid);
1246 : : }
1247 [ # # ]: 0 : TransactionIdRetreat(latestObservedXid); /* = running->nextXid - 1 */
1248 : :
1249 : : /* ----------
1250 : : * Now we've got the running xids we need to set the global values that
1251 : : * are used to track snapshots as they evolve further.
1252 : : *
1253 : : * - latestCompletedXid which will be the xmax for snapshots
1254 : : * - lastOverflowedXid which shows whether snapshots overflow
1255 : : * - nextXid
1256 : : *
1257 : : * If the snapshot overflowed, then we still initialise with what we know,
1258 : : * but the recovery snapshot isn't fully valid yet because we know there
1259 : : * are some subxids missing. We don't know the specific subxids that are
1260 : : * missing, so conservatively assume the last one is latestObservedXid.
1261 : : * ----------
1262 : : */
1263 [ # # ]: 0 : if (running->subxid_status == SUBXIDS_MISSING)
1264 : : {
1265 : 0 : standbyState = STANDBY_SNAPSHOT_PENDING;
1266 : :
1267 : 0 : standbySnapshotPendingXmin = latestObservedXid;
1268 : 0 : procArray->lastOverflowedXid = latestObservedXid;
1269 : 0 : }
1270 : : else
1271 : : {
1272 : 0 : standbyState = STANDBY_SNAPSHOT_READY;
1273 : :
1274 : 0 : standbySnapshotPendingXmin = InvalidTransactionId;
1275 : :
1276 : : /*
1277 : : * If the 'xids' array didn't include all subtransactions, we have to
1278 : : * mark any snapshots taken as overflowed.
1279 : : */
1280 [ # # ]: 0 : if (running->subxid_status == SUBXIDS_IN_SUBTRANS)
1281 : 0 : procArray->lastOverflowedXid = latestObservedXid;
1282 : : else
1283 : : {
1284 [ # # ]: 0 : Assert(running->subxid_status == SUBXIDS_IN_ARRAY);
1285 : 0 : procArray->lastOverflowedXid = InvalidTransactionId;
1286 : : }
1287 : : }
1288 : :
1289 : : /*
1290 : : * If a transaction wrote a commit record in the gap between taking and
1291 : : * logging the snapshot then latestCompletedXid may already be higher than
1292 : : * the value from the snapshot, so check before we use the incoming value.
1293 : : * It also might not yet be set at all.
1294 : : */
1295 : 0 : MaintainLatestCompletedXidRecovery(running->latestCompletedXid);
1296 : :
1297 : : /*
1298 : : * NB: No need to increment TransamVariables->xactCompletionCount here,
1299 : : * nobody can see it yet.
1300 : : */
1301 : :
1302 : 0 : LWLockRelease(ProcArrayLock);
1303 : :
1304 : 0 : KnownAssignedXidsDisplay(DEBUG3);
1305 [ # # ]: 0 : if (standbyState == STANDBY_SNAPSHOT_READY)
1306 [ # # # # ]: 0 : elog(DEBUG1, "recovery snapshots are now enabled");
1307 : : else
1308 [ # # # # ]: 0 : elog(DEBUG1,
1309 : : "recovery snapshot waiting for non-overflowed snapshot or "
1310 : : "until oldest active xid on standby is at least %u (now %u)",
1311 : : standbySnapshotPendingXmin,
1312 : : running->oldestRunningXid);
1313 : 0 : }
1314 : :
1315 : : /*
1316 : : * ProcArrayApplyXidAssignment
1317 : : * Process an XLOG_XACT_ASSIGNMENT WAL record
1318 : : */
1319 : : void
1320 : 0 : ProcArrayApplyXidAssignment(TransactionId topxid,
1321 : : int nsubxids, TransactionId *subxids)
1322 : : {
1323 : 0 : TransactionId max_xid;
1324 : 0 : int i;
1325 : :
1326 [ # # ]: 0 : Assert(standbyState >= STANDBY_INITIALIZED);
1327 : :
1328 : 0 : max_xid = TransactionIdLatest(topxid, nsubxids, subxids);
1329 : :
1330 : : /*
1331 : : * Mark all the subtransactions as observed.
1332 : : *
1333 : : * NOTE: This will fail if the subxid contains too many previously
1334 : : * unobserved xids to fit into known-assigned-xids. That shouldn't happen
1335 : : * as the code stands, because xid-assignment records should never contain
1336 : : * more than PGPROC_MAX_CACHED_SUBXIDS entries.
1337 : : */
1338 : 0 : RecordKnownAssignedTransactionIds(max_xid);
1339 : :
1340 : : /*
1341 : : * Notice that we update pg_subtrans with the top-level xid, rather than
1342 : : * the parent xid. This is a difference between normal processing and
1343 : : * recovery, yet is still correct in all cases. The reason is that
1344 : : * subtransaction commit is not marked in clog until commit processing, so
1345 : : * all aborted subtransactions have already been clearly marked in clog.
1346 : : * As a result we are able to refer directly to the top-level
1347 : : * transaction's state rather than skipping through all the intermediate
1348 : : * states in the subtransaction tree. This should be the first time we
1349 : : * have attempted to SubTransSetParent().
1350 : : */
1351 [ # # ]: 0 : for (i = 0; i < nsubxids; i++)
1352 : 0 : SubTransSetParent(subxids[i], topxid);
1353 : :
1354 : : /* KnownAssignedXids isn't maintained yet, so we're done for now */
1355 [ # # ]: 0 : if (standbyState == STANDBY_INITIALIZED)
1356 : 0 : return;
1357 : :
1358 : : /*
1359 : : * Uses same locking as transaction commit
1360 : : */
1361 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1362 : :
1363 : : /*
1364 : : * Remove subxids from known-assigned-xacts.
1365 : : */
1366 : 0 : KnownAssignedXidsRemoveTree(InvalidTransactionId, nsubxids, subxids);
1367 : :
1368 : : /*
1369 : : * Advance lastOverflowedXid to be at least the last of these subxids.
1370 : : */
1371 [ # # ]: 0 : if (TransactionIdPrecedes(procArray->lastOverflowedXid, max_xid))
1372 : 0 : procArray->lastOverflowedXid = max_xid;
1373 : :
1374 : 0 : LWLockRelease(ProcArrayLock);
1375 [ # # ]: 0 : }
1376 : :
1377 : : /*
1378 : : * TransactionIdIsInProgress -- is given transaction running in some backend
1379 : : *
1380 : : * Aside from some shortcuts such as checking RecentXmin and our own Xid,
1381 : : * there are four possibilities for finding a running transaction:
1382 : : *
1383 : : * 1. The given Xid is a main transaction Id. We will find this out cheaply
1384 : : * by looking at ProcGlobal->xids.
1385 : : *
1386 : : * 2. The given Xid is one of the cached subxact Xids in the PGPROC array.
1387 : : * We can find this out cheaply too.
1388 : : *
1389 : : * 3. In Hot Standby mode, we must search the KnownAssignedXids list to see
1390 : : * if the Xid is running on the primary.
1391 : : *
1392 : : * 4. Search the SubTrans tree to find the Xid's topmost parent, and then see
1393 : : * if that is running according to ProcGlobal->xids[] or KnownAssignedXids.
1394 : : * This is the slowest way, but sadly it has to be done always if the others
1395 : : * failed, unless we see that the cached subxact sets are complete (none have
1396 : : * overflowed).
1397 : : *
1398 : : * ProcArrayLock has to be held while we do 1, 2, 3. If we save the top Xids
1399 : : * while doing 1 and 3, we can release the ProcArrayLock while we do 4.
1400 : : * This buys back some concurrency (and we can't retrieve the main Xids from
1401 : : * ProcGlobal->xids[] again anyway; see GetNewTransactionId).
1402 : : */
1403 : : bool
1404 : 1535024 : TransactionIdIsInProgress(TransactionId xid)
1405 : : {
1406 : : static TransactionId *xids = NULL;
1407 : : static TransactionId *other_xids;
1408 : 1535024 : XidCacheStatus *other_subxidstates;
1409 : 1535024 : int nxids = 0;
1410 : 1535024 : ProcArrayStruct *arrayP = procArray;
1411 : 1535024 : TransactionId topxid;
1412 : 1535024 : TransactionId latestCompletedXid;
1413 : 1535024 : int mypgxactoff;
1414 : 1535024 : int numProcs;
1415 : 1535024 : int j;
1416 : :
1417 : : /*
1418 : : * Don't bother checking a transaction older than RecentXmin; it could not
1419 : : * possibly still be running. (Note: in particular, this guarantees that
1420 : : * we reject InvalidTransactionId, FrozenTransactionId, etc as not
1421 : : * running.)
1422 : : */
1423 [ + + ]: 1535024 : if (TransactionIdPrecedes(xid, RecentXmin))
1424 : : {
1425 : : xc_by_recent_xmin_inc();
1426 : 1181024 : return false;
1427 : : }
1428 : :
1429 : : /*
1430 : : * We may have just checked the status of this transaction, so if it is
1431 : : * already known to be completed, we can fall out without any access to
1432 : : * shared memory.
1433 : : */
1434 [ + + ]: 354000 : if (TransactionIdEquals(cachedXidIsNotInProgress, xid))
1435 : : {
1436 : : xc_by_known_xact_inc();
1437 : 346407 : return false;
1438 : : }
1439 : :
1440 : : /*
1441 : : * Also, we can handle our own transaction (and subtransactions) without
1442 : : * any access to shared memory.
1443 : : */
1444 [ + + ]: 7593 : if (TransactionIdIsCurrentTransactionId(xid))
1445 : : {
1446 : : xc_by_my_xact_inc();
1447 : 3152 : return true;
1448 : : }
1449 : :
1450 : : /*
1451 : : * If first time through, get workspace to remember main XIDs in. We
1452 : : * malloc it permanently to avoid repeated palloc/pfree overhead.
1453 : : */
1454 [ + + ]: 4441 : if (xids == NULL)
1455 : : {
1456 : : /*
1457 : : * In hot standby mode, reserve enough space to hold all xids in the
1458 : : * known-assigned list. If we later finish recovery, we no longer need
1459 : : * the bigger array, but we don't bother to shrink it.
1460 : : */
1461 [ - + ]: 154 : int maxxids = RecoveryInProgress() ? TOTAL_MAX_CACHED_SUBXIDS : arrayP->maxProcs;
1462 : :
1463 : 154 : xids = (TransactionId *) malloc(maxxids * sizeof(TransactionId));
1464 [ + - ]: 154 : if (xids == NULL)
1465 [ # # # # ]: 0 : ereport(ERROR,
1466 : : (errcode(ERRCODE_OUT_OF_MEMORY),
1467 : : errmsg("out of memory")));
1468 : 154 : }
1469 : :
1470 : 4441 : other_xids = ProcGlobal->xids;
1471 : 4441 : other_subxidstates = ProcGlobal->subxidStates;
1472 : :
1473 : 4441 : LWLockAcquire(ProcArrayLock, LW_SHARED);
1474 : :
1475 : : /*
1476 : : * Now that we have the lock, we can check latestCompletedXid; if the
1477 : : * target Xid is after that, it's surely still running.
1478 : : */
1479 : 4441 : latestCompletedXid =
1480 : 4441 : XidFromFullTransactionId(TransamVariables->latestCompletedXid);
1481 [ + + ]: 4441 : if (TransactionIdPrecedes(latestCompletedXid, xid))
1482 : : {
1483 : 259 : LWLockRelease(ProcArrayLock);
1484 : : xc_by_latest_xid_inc();
1485 : 259 : return true;
1486 : : }
1487 : :
1488 : : /* No shortcuts, gotta grovel through the array */
1489 : 4182 : mypgxactoff = MyProc->pgxactoff;
1490 : 4182 : numProcs = arrayP->numProcs;
1491 [ + + + + ]: 47232 : for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
1492 : : {
1493 : 43050 : int pgprocno;
1494 : 43050 : PGPROC *proc;
1495 : 43050 : TransactionId pxid;
1496 : 43050 : int pxids;
1497 : :
1498 : : /* Ignore ourselves --- dealt with it above */
1499 [ + + ]: 43050 : if (pgxactoff == mypgxactoff)
1500 : 3935 : continue;
1501 : :
1502 : : /* Fetch xid just once - see GetNewTransactionId */
1503 : 39115 : pxid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
1504 : :
1505 [ + + ]: 39115 : if (!TransactionIdIsValid(pxid))
1506 : 27477 : continue;
1507 : :
1508 : : /*
1509 : : * Step 1: check the main Xid
1510 : : */
1511 [ + + ]: 11638 : if (TransactionIdEquals(pxid, xid))
1512 : : {
1513 : 465 : LWLockRelease(ProcArrayLock);
1514 : : xc_by_main_xid_inc();
1515 : 465 : return true;
1516 : : }
1517 : :
1518 : : /*
1519 : : * We can ignore main Xids that are younger than the target Xid, since
1520 : : * the target could not possibly be their child.
1521 : : */
1522 [ + + ]: 11173 : if (TransactionIdPrecedes(xid, pxid))
1523 : 5407 : continue;
1524 : :
1525 : : /*
1526 : : * Step 2: check the cached child-Xids arrays
1527 : : */
1528 : 5766 : pxids = other_subxidstates[pgxactoff].count;
1529 : 5766 : pg_read_barrier(); /* pairs with barrier in GetNewTransactionId() */
1530 : 5766 : pgprocno = arrayP->pgprocnos[pgxactoff];
1531 : 5766 : proc = &allProcs[pgprocno];
1532 [ + + ]: 5790 : for (j = pxids - 1; j >= 0; j--)
1533 : : {
1534 : : /* Fetch xid just once - see GetNewTransactionId */
1535 : 24 : TransactionId cxid = UINT32_ACCESS_ONCE(proc->subxids.xids[j]);
1536 : :
1537 [ - + ]: 24 : if (TransactionIdEquals(cxid, xid))
1538 : : {
1539 : 0 : LWLockRelease(ProcArrayLock);
1540 : : xc_by_child_xid_inc();
1541 : 0 : return true;
1542 : : }
1543 [ - + ]: 24 : }
1544 : :
1545 : : /*
1546 : : * Save the main Xid for step 4. We only need to remember main Xids
1547 : : * that have uncached children. (Note: there is no race condition
1548 : : * here because the overflowed flag cannot be cleared, only set, while
1549 : : * we hold ProcArrayLock. So we can't miss an Xid that we need to
1550 : : * worry about.)
1551 : : */
1552 [ + - ]: 5766 : if (other_subxidstates[pgxactoff].overflowed)
1553 : 0 : xids[nxids++] = pxid;
1554 [ + + + ]: 43050 : }
1555 : :
1556 : : /*
1557 : : * Step 3: in hot standby mode, check the known-assigned-xids list. XIDs
1558 : : * in the list must be treated as running.
1559 : : */
1560 [ + - ]: 3717 : if (RecoveryInProgress())
1561 : : {
1562 : : /* none of the PGPROC entries should have XIDs in hot standby mode */
1563 [ # # ]: 0 : Assert(nxids == 0);
1564 : :
1565 [ # # ]: 0 : if (KnownAssignedXidExists(xid))
1566 : : {
1567 : 0 : LWLockRelease(ProcArrayLock);
1568 : : xc_by_known_assigned_inc();
1569 : 0 : return true;
1570 : : }
1571 : :
1572 : : /*
1573 : : * If the KnownAssignedXids overflowed, we have to check pg_subtrans
1574 : : * too. Fetch all xids from KnownAssignedXids that are lower than
1575 : : * xid, since if xid is a subtransaction its parent will always have a
1576 : : * lower value. Note we will collect both main and subXIDs here, but
1577 : : * there's no help for it.
1578 : : */
1579 [ # # ]: 0 : if (TransactionIdPrecedesOrEquals(xid, procArray->lastOverflowedXid))
1580 : 0 : nxids = KnownAssignedXidsGet(xids, xid);
1581 : 0 : }
1582 : :
1583 : 3717 : LWLockRelease(ProcArrayLock);
1584 : :
1585 : : /*
1586 : : * If none of the relevant caches overflowed, we know the Xid is not
1587 : : * running without even looking at pg_subtrans.
1588 : : */
1589 [ - + ]: 3717 : if (nxids == 0)
1590 : : {
1591 : : xc_no_overflow_inc();
1592 : 3717 : cachedXidIsNotInProgress = xid;
1593 : 3717 : return false;
1594 : : }
1595 : :
1596 : : /*
1597 : : * Step 4: have to check pg_subtrans.
1598 : : *
1599 : : * At this point, we know it's either a subtransaction of one of the Xids
1600 : : * in xids[], or it's not running. If it's an already-failed
1601 : : * subtransaction, we want to say "not running" even though its parent may
1602 : : * still be running. So first, check pg_xact to see if it's been aborted.
1603 : : */
1604 : : xc_slow_answer_inc();
1605 : :
1606 [ # # ]: 0 : if (TransactionIdDidAbort(xid))
1607 : : {
1608 : 0 : cachedXidIsNotInProgress = xid;
1609 : 0 : return false;
1610 : : }
1611 : :
1612 : : /*
1613 : : * It isn't aborted, so check whether the transaction tree it belongs to
1614 : : * is still running (or, more precisely, whether it was running when we
1615 : : * held ProcArrayLock).
1616 : : */
1617 : 0 : topxid = SubTransGetTopmostTransaction(xid);
1618 [ # # ]: 0 : Assert(TransactionIdIsValid(topxid));
1619 [ # # # # ]: 0 : if (!TransactionIdEquals(topxid, xid) &&
1620 : 0 : pg_lfind32(topxid, xids, nxids))
1621 : 0 : return true;
1622 : :
1623 : 0 : cachedXidIsNotInProgress = xid;
1624 : 0 : return false;
1625 : 1535024 : }
1626 : :
1627 : :
1628 : : /*
1629 : : * Determine XID horizons.
1630 : : *
1631 : : * This is used by wrapper functions like GetOldestNonRemovableTransactionId()
1632 : : * (for VACUUM), GetReplicationHorizons() (for hot_standby_feedback), etc as
1633 : : * well as "internally" by GlobalVisUpdate() (see comment above struct
1634 : : * GlobalVisState).
1635 : : *
1636 : : * See the definition of ComputeXidHorizonsResult for the various computed
1637 : : * horizons.
1638 : : *
1639 : : * For VACUUM separate horizons (used to decide which deleted tuples must
1640 : : * be preserved), for shared and non-shared tables are computed. For shared
1641 : : * relations backends in all databases must be considered, but for non-shared
1642 : : * relations that's not required, since only backends in my own database could
1643 : : * ever see the tuples in them. Also, we can ignore concurrently running lazy
1644 : : * VACUUMs because (a) they must be working on other tables, and (b) they
1645 : : * don't need to do snapshot-based lookups.
1646 : : *
1647 : : * This also computes a horizon used to truncate pg_subtrans. For that
1648 : : * backends in all databases have to be considered, and concurrently running
1649 : : * lazy VACUUMs cannot be ignored, as they still may perform pg_subtrans
1650 : : * accesses.
1651 : : *
1652 : : * Note: we include all currently running xids in the set of considered xids.
1653 : : * This ensures that if a just-started xact has not yet set its snapshot,
1654 : : * when it does set the snapshot it cannot set xmin less than what we compute.
1655 : : * See notes in src/backend/access/transam/README.
1656 : : *
1657 : : * Note: despite the above, it's possible for the calculated values to move
1658 : : * backwards on repeated calls. The calculated values are conservative, so
1659 : : * that anything older is definitely not considered as running by anyone
1660 : : * anymore, but the exact values calculated depend on a number of things. For
1661 : : * example, if there are no transactions running in the current database, the
1662 : : * horizon for normal tables will be latestCompletedXid. If a transaction
1663 : : * begins after that, its xmin will include in-progress transactions in other
1664 : : * databases that started earlier, so another call will return a lower value.
1665 : : * Nonetheless it is safe to vacuum a table in the current database with the
1666 : : * first result. There are also replication-related effects: a walsender
1667 : : * process can set its xmin based on transactions that are no longer running
1668 : : * on the primary but are still being replayed on the standby, thus possibly
1669 : : * making the values go backwards. In this case there is a possibility that
1670 : : * we lose data that the standby would like to have, but unless the standby
1671 : : * uses a replication slot to make its xmin persistent there is little we can
1672 : : * do about that --- data is only protected if the walsender runs continuously
1673 : : * while queries are executed on the standby. (The Hot Standby code deals
1674 : : * with such cases by failing standby queries that needed to access
1675 : : * already-removed data, so there's no integrity bug.)
1676 : : *
1677 : : * Note: the approximate horizons (see definition of GlobalVisState) are
1678 : : * updated by the computations done here. That's currently required for
1679 : : * correctness and a small optimization. Without doing so it's possible that
1680 : : * heap vacuum's call to heap_page_prune_and_freeze() uses a more conservative
1681 : : * horizon than later when deciding which tuples can be removed - which the
1682 : : * code doesn't expect (breaking HOT).
1683 : : */
1684 : : static void
1685 : 13658 : ComputeXidHorizons(ComputeXidHorizonsResult *h)
1686 : : {
1687 : 13658 : ProcArrayStruct *arrayP = procArray;
1688 : 13658 : TransactionId kaxmin;
1689 : 13658 : bool in_recovery = RecoveryInProgress();
1690 : 13658 : TransactionId *other_xids = ProcGlobal->xids;
1691 : :
1692 : : /* inferred after ProcArrayLock is released */
1693 : 13658 : h->catalog_oldest_nonremovable = InvalidTransactionId;
1694 : :
1695 : 13658 : LWLockAcquire(ProcArrayLock, LW_SHARED);
1696 : :
1697 : 13658 : h->latest_completed = TransamVariables->latestCompletedXid;
1698 : :
1699 : : /*
1700 : : * We initialize the MIN() calculation with latestCompletedXid + 1. This
1701 : : * is a lower bound for the XIDs that might appear in the ProcArray later,
1702 : : * and so protects us against overestimating the result due to future
1703 : : * additions.
1704 : : */
1705 : : {
1706 : 13658 : TransactionId initial;
1707 : :
1708 : 13658 : initial = XidFromFullTransactionId(h->latest_completed);
1709 [ + - ]: 13658 : Assert(TransactionIdIsValid(initial));
1710 [ + - ]: 13658 : TransactionIdAdvance(initial);
1711 : :
1712 : 13658 : h->oldest_considered_running = initial;
1713 : 13658 : h->shared_oldest_nonremovable = initial;
1714 : 13658 : h->data_oldest_nonremovable = initial;
1715 : :
1716 : : /*
1717 : : * Only modifications made by this backend affect the horizon for
1718 : : * temporary relations. Instead of a check in each iteration of the
1719 : : * loop over all PGPROCs it is cheaper to just initialize to the
1720 : : * current top-level xid any.
1721 : : *
1722 : : * Without an assigned xid we could use a horizon as aggressive as
1723 : : * GetNewTransactionId(), but we can get away with the much cheaper
1724 : : * latestCompletedXid + 1: If this backend has no xid there, by
1725 : : * definition, can't be any newer changes in the temp table than
1726 : : * latestCompletedXid.
1727 : : */
1728 [ + + ]: 13658 : if (TransactionIdIsValid(MyProc->xid))
1729 : 5588 : h->temp_oldest_nonremovable = MyProc->xid;
1730 : : else
1731 : 8070 : h->temp_oldest_nonremovable = initial;
1732 : 13658 : }
1733 : :
1734 : : /*
1735 : : * Fetch slot horizons while ProcArrayLock is held - the
1736 : : * LWLockAcquire/LWLockRelease are a barrier, ensuring this happens inside
1737 : : * the lock.
1738 : : */
1739 : 13658 : h->slot_xmin = procArray->replication_slot_xmin;
1740 : 13658 : h->slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
1741 : :
1742 [ + + ]: 114823 : for (int index = 0; index < arrayP->numProcs; index++)
1743 : : {
1744 : 101165 : int pgprocno = arrayP->pgprocnos[index];
1745 : 101165 : PGPROC *proc = &allProcs[pgprocno];
1746 : 101165 : int8 statusFlags = ProcGlobal->statusFlags[index];
1747 : 101165 : TransactionId xid;
1748 : 101165 : TransactionId xmin;
1749 : :
1750 : : /* Fetch xid just once - see GetNewTransactionId */
1751 : 101165 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
1752 : 101165 : xmin = UINT32_ACCESS_ONCE(proc->xmin);
1753 : :
1754 : : /*
1755 : : * Consider both the transaction's Xmin, and its Xid.
1756 : : *
1757 : : * We must check both because a transaction might have an Xmin but not
1758 : : * (yet) an Xid; conversely, if it has an Xid, that could determine
1759 : : * some not-yet-set Xmin.
1760 : : */
1761 : 101165 : xmin = TransactionIdOlder(xmin, xid);
1762 : :
1763 : : /* if neither is set, this proc doesn't influence the horizon */
1764 [ + + ]: 101165 : if (!TransactionIdIsValid(xmin))
1765 : 55819 : continue;
1766 : :
1767 : : /*
1768 : : * Don't ignore any procs when determining which transactions might be
1769 : : * considered running. While slots should ensure logical decoding
1770 : : * backends are protected even without this check, it can't hurt to
1771 : : * include them here as well..
1772 : : */
1773 : 45346 : h->oldest_considered_running =
1774 : 45346 : TransactionIdOlder(h->oldest_considered_running, xmin);
1775 : :
1776 : : /*
1777 : : * Skip over backends either vacuuming (which is ok with rows being
1778 : : * removed, as long as pg_subtrans is not truncated) or doing logical
1779 : : * decoding (which manages xmin separately, check below).
1780 : : */
1781 [ + + ]: 45346 : if (statusFlags & (PROC_IN_VACUUM | PROC_IN_LOGICAL_DECODING))
1782 : 1512 : continue;
1783 : :
1784 : : /* shared tables need to take backends in all databases into account */
1785 : 43834 : h->shared_oldest_nonremovable =
1786 : 43834 : TransactionIdOlder(h->shared_oldest_nonremovable, xmin);
1787 : :
1788 : : /*
1789 : : * Normally sessions in other databases are ignored for anything but
1790 : : * the shared horizon.
1791 : : *
1792 : : * However, include them when MyDatabaseId is not (yet) set. A
1793 : : * backend in the process of starting up must not compute a "too
1794 : : * aggressive" horizon, otherwise we could end up using it to prune
1795 : : * still-needed data away. If the current backend never connects to a
1796 : : * database this is harmless, because data_oldest_nonremovable will
1797 : : * never be utilized.
1798 : : *
1799 : : * Also, sessions marked with PROC_AFFECTS_ALL_HORIZONS should always
1800 : : * be included. (This flag is used for hot standby feedback, which
1801 : : * can't be tied to a specific database.)
1802 : : *
1803 : : * Also, while in recovery we cannot compute an accurate per-database
1804 : : * horizon, as all xids are managed via the KnownAssignedXids
1805 : : * machinery.
1806 : : */
1807 [ + + ]: 43834 : if (proc->databaseId == MyDatabaseId ||
1808 [ + + ]: 1500 : MyDatabaseId == InvalidOid ||
1809 [ + - - + ]: 36 : (statusFlags & PROC_AFFECTS_ALL_HORIZONS) ||
1810 : 36 : in_recovery)
1811 : : {
1812 : 43798 : h->data_oldest_nonremovable =
1813 : 43798 : TransactionIdOlder(h->data_oldest_nonremovable, xmin);
1814 : 43798 : }
1815 [ - + + ]: 101165 : }
1816 : :
1817 : : /*
1818 : : * If in recovery fetch oldest xid in KnownAssignedXids, will be applied
1819 : : * after lock is released.
1820 : : */
1821 [ + - ]: 13658 : if (in_recovery)
1822 : 0 : kaxmin = KnownAssignedXidsGetOldestXmin();
1823 : :
1824 : : /*
1825 : : * No other information from shared state is needed, release the lock
1826 : : * immediately. The rest of the computations can be done without a lock.
1827 : : */
1828 : 13658 : LWLockRelease(ProcArrayLock);
1829 : :
1830 [ + - ]: 13658 : if (in_recovery)
1831 : : {
1832 : 0 : h->oldest_considered_running =
1833 : 0 : TransactionIdOlder(h->oldest_considered_running, kaxmin);
1834 : 0 : h->shared_oldest_nonremovable =
1835 : 0 : TransactionIdOlder(h->shared_oldest_nonremovable, kaxmin);
1836 : 0 : h->data_oldest_nonremovable =
1837 : 0 : TransactionIdOlder(h->data_oldest_nonremovable, kaxmin);
1838 : : /* temp relations cannot be accessed in recovery */
1839 : 0 : }
1840 : :
1841 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1842 : : h->shared_oldest_nonremovable));
1843 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1844 : : h->data_oldest_nonremovable));
1845 : :
1846 : : /*
1847 : : * Check whether there are replication slots requiring an older xmin.
1848 : : */
1849 : 13658 : h->shared_oldest_nonremovable =
1850 : 13658 : TransactionIdOlder(h->shared_oldest_nonremovable, h->slot_xmin);
1851 : 13658 : h->data_oldest_nonremovable =
1852 : 13658 : TransactionIdOlder(h->data_oldest_nonremovable, h->slot_xmin);
1853 : :
1854 : : /*
1855 : : * The only difference between catalog / data horizons is that the slot's
1856 : : * catalog xmin is applied to the catalog one (so catalogs can be accessed
1857 : : * for logical decoding). Initialize with data horizon, and then back up
1858 : : * further if necessary. Have to back up the shared horizon as well, since
1859 : : * that also can contain catalogs.
1860 : : */
1861 : 13658 : h->shared_oldest_nonremovable_raw = h->shared_oldest_nonremovable;
1862 : 13658 : h->shared_oldest_nonremovable =
1863 : 27316 : TransactionIdOlder(h->shared_oldest_nonremovable,
1864 : 13658 : h->slot_catalog_xmin);
1865 : 13658 : h->catalog_oldest_nonremovable = h->data_oldest_nonremovable;
1866 : 13658 : h->catalog_oldest_nonremovable =
1867 : 27316 : TransactionIdOlder(h->catalog_oldest_nonremovable,
1868 : 13658 : h->slot_catalog_xmin);
1869 : :
1870 : : /*
1871 : : * It's possible that slots backed up the horizons further than
1872 : : * oldest_considered_running. Fix.
1873 : : */
1874 : 13658 : h->oldest_considered_running =
1875 : 27316 : TransactionIdOlder(h->oldest_considered_running,
1876 : 13658 : h->shared_oldest_nonremovable);
1877 : 13658 : h->oldest_considered_running =
1878 : 27316 : TransactionIdOlder(h->oldest_considered_running,
1879 : 13658 : h->catalog_oldest_nonremovable);
1880 : 13658 : h->oldest_considered_running =
1881 : 27316 : TransactionIdOlder(h->oldest_considered_running,
1882 : 13658 : h->data_oldest_nonremovable);
1883 : :
1884 : : /*
1885 : : * shared horizons have to be at least as old as the oldest visible in
1886 : : * current db
1887 : : */
1888 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1889 : : h->data_oldest_nonremovable));
1890 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1891 : : h->catalog_oldest_nonremovable));
1892 : :
1893 : : /*
1894 : : * Horizons need to ensure that pg_subtrans access is still possible for
1895 : : * the relevant backends.
1896 : : */
1897 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1898 : : h->shared_oldest_nonremovable));
1899 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1900 : : h->catalog_oldest_nonremovable));
1901 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1902 : : h->data_oldest_nonremovable));
1903 [ + - ]: 13658 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1904 : : h->temp_oldest_nonremovable));
1905 [ - + # # ]: 13658 : Assert(!TransactionIdIsValid(h->slot_xmin) ||
1906 : : TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1907 : : h->slot_xmin));
1908 [ - + # # ]: 13658 : Assert(!TransactionIdIsValid(h->slot_catalog_xmin) ||
1909 : : TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1910 : : h->slot_catalog_xmin));
1911 : :
1912 : : /* update approximate horizons with the computed horizons */
1913 : 13658 : GlobalVisUpdateApply(h);
1914 : 13658 : }
1915 : :
1916 : : /*
1917 : : * Determine what kind of visibility horizon needs to be used for a
1918 : : * relation. If rel is NULL, the most conservative horizon is used.
1919 : : */
1920 : : static inline GlobalVisHorizonKind
1921 : 4374197 : GlobalVisHorizonKindForRel(Relation rel)
1922 : : {
1923 : : /*
1924 : : * Other relkinds currently don't contain xids, nor always the necessary
1925 : : * logical decoding markers.
1926 : : */
1927 [ + + + + : 4374197 : Assert(!rel ||
+ + + - ]
1928 : : rel->rd_rel->relkind == RELKIND_RELATION ||
1929 : : rel->rd_rel->relkind == RELKIND_MATVIEW ||
1930 : : rel->rd_rel->relkind == RELKIND_TOASTVALUE);
1931 : :
1932 [ + + + + : 4374197 : if (rel == NULL || rel->rd_rel->relisshared || RecoveryInProgress())
- + ]
1933 : 10867 : return VISHORIZON_SHARED;
1934 [ + + # # ]: 4363330 : else if (IsCatalogRelation(rel) ||
1935 [ + - - + : 3684807 : RelationIsAccessibleInLogicalDecoding(rel))
# # # # #
# # # #
# ]
1936 : 678523 : return VISHORIZON_CATALOG;
1937 [ + + + + ]: 3684807 : else if (!RELATION_IS_LOCAL(rel))
1938 : 3671862 : return VISHORIZON_DATA;
1939 : : else
1940 : 12945 : return VISHORIZON_TEMP;
1941 : 4374197 : }
1942 : :
1943 : : /*
1944 : : * Return the oldest XID for which deleted tuples must be preserved in the
1945 : : * passed table.
1946 : : *
1947 : : * If rel is not NULL the horizon may be considerably more recent than
1948 : : * otherwise (i.e. fewer tuples will be removable). In the NULL case a horizon
1949 : : * that is correct (but not optimal) for all relations will be returned.
1950 : : *
1951 : : * This is used by VACUUM to decide which deleted tuples must be preserved in
1952 : : * the passed in table.
1953 : : */
1954 : : TransactionId
1955 : 5734 : GetOldestNonRemovableTransactionId(Relation rel)
1956 : : {
1957 : 5734 : ComputeXidHorizonsResult horizons;
1958 : :
1959 : 5734 : ComputeXidHorizons(&horizons);
1960 : :
1961 [ + - + + : 5734 : switch (GlobalVisHorizonKindForRel(rel))
+ ]
1962 : : {
1963 : : case VISHORIZON_SHARED:
1964 : 238 : return horizons.shared_oldest_nonremovable;
1965 : : case VISHORIZON_CATALOG:
1966 : 230 : return horizons.catalog_oldest_nonremovable;
1967 : : case VISHORIZON_DATA:
1968 : 2759 : return horizons.data_oldest_nonremovable;
1969 : : case VISHORIZON_TEMP:
1970 : 2507 : return horizons.temp_oldest_nonremovable;
1971 : : }
1972 : :
1973 : : /* just to prevent compiler warnings */
1974 : 0 : return InvalidTransactionId;
1975 : 5734 : }
1976 : :
1977 : : /*
1978 : : * Return the oldest transaction id any currently running backend might still
1979 : : * consider running. This should not be used for visibility / pruning
1980 : : * determinations (see GetOldestNonRemovableTransactionId()), but for
1981 : : * decisions like up to where pg_subtrans can be truncated.
1982 : : */
1983 : : TransactionId
1984 : 7 : GetOldestTransactionIdConsideredRunning(void)
1985 : : {
1986 : 7 : ComputeXidHorizonsResult horizons;
1987 : :
1988 : 7 : ComputeXidHorizons(&horizons);
1989 : :
1990 : 14 : return horizons.oldest_considered_running;
1991 : 7 : }
1992 : :
1993 : : /*
1994 : : * Return the visibility horizons for a hot standby feedback message.
1995 : : */
1996 : : void
1997 : 0 : GetReplicationHorizons(TransactionId *xmin, TransactionId *catalog_xmin)
1998 : : {
1999 : 0 : ComputeXidHorizonsResult horizons;
2000 : :
2001 : 0 : ComputeXidHorizons(&horizons);
2002 : :
2003 : : /*
2004 : : * Don't want to use shared_oldest_nonremovable here, as that contains the
2005 : : * effect of replication slot's catalog_xmin. We want to send a separate
2006 : : * feedback for the catalog horizon, so the primary can remove data table
2007 : : * contents more aggressively.
2008 : : */
2009 : 0 : *xmin = horizons.shared_oldest_nonremovable_raw;
2010 : 0 : *catalog_xmin = horizons.slot_catalog_xmin;
2011 : 0 : }
2012 : :
2013 : : /*
2014 : : * GetMaxSnapshotXidCount -- get max size for snapshot XID array
2015 : : *
2016 : : * We have to export this for use by snapmgr.c.
2017 : : */
2018 : : int
2019 : 2127 : GetMaxSnapshotXidCount(void)
2020 : : {
2021 : 2127 : return procArray->maxProcs;
2022 : : }
2023 : :
2024 : : /*
2025 : : * GetMaxSnapshotSubxidCount -- get max size for snapshot sub-XID array
2026 : : *
2027 : : * We have to export this for use by snapmgr.c.
2028 : : */
2029 : : int
2030 : 2127 : GetMaxSnapshotSubxidCount(void)
2031 : : {
2032 : 2127 : return TOTAL_MAX_CACHED_SUBXIDS;
2033 : : }
2034 : :
2035 : : /*
2036 : : * Helper function for GetSnapshotData() that checks if the bulk of the
2037 : : * visibility information in the snapshot is still valid. If so, it updates
2038 : : * the fields that need to change and returns true. Otherwise it returns
2039 : : * false.
2040 : : *
2041 : : * This very likely can be evolved to not need ProcArrayLock held (at very
2042 : : * least in the case we already hold a snapshot), but that's for another day.
2043 : : */
2044 : : static bool
2045 : 705687 : GetSnapshotDataReuse(Snapshot snapshot)
2046 : : {
2047 : 705687 : uint64 curXactCompletionCount;
2048 : :
2049 [ + - ]: 705687 : Assert(LWLockHeldByMe(ProcArrayLock));
2050 : :
2051 [ + + ]: 705687 : if (unlikely(snapshot->snapXactCompletionCount == 0))
2052 : 1871 : return false;
2053 : :
2054 : 703816 : curXactCompletionCount = TransamVariables->xactCompletionCount;
2055 [ + + ]: 703816 : if (curXactCompletionCount != snapshot->snapXactCompletionCount)
2056 : 83593 : return false;
2057 : :
2058 : : /*
2059 : : * If the current xactCompletionCount is still the same as it was at the
2060 : : * time the snapshot was built, we can be sure that rebuilding the
2061 : : * contents of the snapshot the hard way would result in the same snapshot
2062 : : * contents:
2063 : : *
2064 : : * As explained in transam/README, the set of xids considered running by
2065 : : * GetSnapshotData() cannot change while ProcArrayLock is held. Snapshot
2066 : : * contents only depend on transactions with xids and xactCompletionCount
2067 : : * is incremented whenever a transaction with an xid finishes (while
2068 : : * holding ProcArrayLock exclusively). Thus the xactCompletionCount check
2069 : : * ensures we would detect if the snapshot would have changed.
2070 : : *
2071 : : * As the snapshot contents are the same as it was before, it is safe to
2072 : : * re-enter the snapshot's xmin into the PGPROC array. None of the rows
2073 : : * visible under the snapshot could already have been removed (that'd
2074 : : * require the set of running transactions to change) and it fulfills the
2075 : : * requirement that concurrent GetSnapshotData() calls yield the same
2076 : : * xmin.
2077 : : */
2078 [ + + ]: 620223 : if (!TransactionIdIsValid(MyProc->xmin))
2079 : 53500 : MyProc->xmin = TransactionXmin = snapshot->xmin;
2080 : :
2081 : 620223 : RecentXmin = snapshot->xmin;
2082 [ + - ]: 620223 : Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
2083 : :
2084 : 620223 : snapshot->curcid = GetCurrentCommandId(false);
2085 : 620223 : snapshot->active_count = 0;
2086 : 620223 : snapshot->regd_count = 0;
2087 : 620223 : snapshot->copied = false;
2088 : :
2089 : 620223 : return true;
2090 : 705687 : }
2091 : :
2092 : : /*
2093 : : * GetSnapshotData -- returns information about running transactions.
2094 : : *
2095 : : * The returned snapshot includes xmin (lowest still-running xact ID),
2096 : : * xmax (highest completed xact ID + 1), and a list of running xact IDs
2097 : : * in the range xmin <= xid < xmax. It is used as follows:
2098 : : * All xact IDs < xmin are considered finished.
2099 : : * All xact IDs >= xmax are considered still running.
2100 : : * For an xact ID xmin <= xid < xmax, consult list to see whether
2101 : : * it is considered running or not.
2102 : : * This ensures that the set of transactions seen as "running" by the
2103 : : * current xact will not change after it takes the snapshot.
2104 : : *
2105 : : * All running top-level XIDs are included in the snapshot, except for lazy
2106 : : * VACUUM processes. We also try to include running subtransaction XIDs,
2107 : : * but since PGPROC has only a limited cache area for subxact XIDs, full
2108 : : * information may not be available. If we find any overflowed subxid arrays,
2109 : : * we have to mark the snapshot's subxid data as overflowed, and extra work
2110 : : * *may* need to be done to determine what's running (see XidInMVCCSnapshot()).
2111 : : *
2112 : : * We also update the following backend-global variables:
2113 : : * TransactionXmin: the oldest xmin of any snapshot in use in the
2114 : : * current transaction (this is the same as MyProc->xmin).
2115 : : * RecentXmin: the xmin computed for the most recent snapshot. XIDs
2116 : : * older than this are known not running any more.
2117 : : *
2118 : : * And try to advance the bounds of GlobalVis{Shared,Catalog,Data,Temp}Rels
2119 : : * for the benefit of the GlobalVisTest* family of functions.
2120 : : *
2121 : : * Note: this function should probably not be called with an argument that's
2122 : : * not statically allocated (see xip allocation below).
2123 : : */
2124 : : Snapshot
2125 : 705687 : GetSnapshotData(Snapshot snapshot)
2126 : : {
2127 : 705687 : ProcArrayStruct *arrayP = procArray;
2128 : 705687 : TransactionId *other_xids = ProcGlobal->xids;
2129 : 705687 : TransactionId xmin;
2130 : 705687 : TransactionId xmax;
2131 : 705687 : int count = 0;
2132 : 705687 : int subcount = 0;
2133 : 705687 : bool suboverflowed = false;
2134 : 705687 : FullTransactionId latest_completed;
2135 : 705687 : TransactionId oldestxid;
2136 : 705687 : int mypgxactoff;
2137 : 705687 : TransactionId myxid;
2138 : 705687 : uint64 curXactCompletionCount;
2139 : :
2140 : 705687 : TransactionId replication_slot_xmin = InvalidTransactionId;
2141 : 705687 : TransactionId replication_slot_catalog_xmin = InvalidTransactionId;
2142 : :
2143 [ + - ]: 705687 : Assert(snapshot != NULL);
2144 : :
2145 : : /*
2146 : : * Allocating space for maxProcs xids is usually overkill; numProcs would
2147 : : * be sufficient. But it seems better to do the malloc while not holding
2148 : : * the lock, so we can't look at numProcs. Likewise, we allocate much
2149 : : * more subxip storage than is probably needed.
2150 : : *
2151 : : * This does open a possibility for avoiding repeated malloc/free: since
2152 : : * maxProcs does not change at runtime, we can simply reuse the previous
2153 : : * xip arrays if any. (This relies on the fact that all callers pass
2154 : : * static SnapshotData structs.)
2155 : : */
2156 [ + + ]: 705687 : if (snapshot->xip == NULL)
2157 : : {
2158 : : /*
2159 : : * First call for this snapshot. Snapshot is same size whether or not
2160 : : * we are in recovery, see later comments.
2161 : : */
2162 : 1650 : snapshot->xip = (TransactionId *)
2163 : 1650 : malloc(GetMaxSnapshotXidCount() * sizeof(TransactionId));
2164 [ + - ]: 1650 : if (snapshot->xip == NULL)
2165 [ # # # # ]: 0 : ereport(ERROR,
2166 : : (errcode(ERRCODE_OUT_OF_MEMORY),
2167 : : errmsg("out of memory")));
2168 [ + - ]: 1650 : Assert(snapshot->subxip == NULL);
2169 : 1650 : snapshot->subxip = (TransactionId *)
2170 : 1650 : malloc(GetMaxSnapshotSubxidCount() * sizeof(TransactionId));
2171 [ + - ]: 1650 : if (snapshot->subxip == NULL)
2172 [ # # # # ]: 0 : ereport(ERROR,
2173 : : (errcode(ERRCODE_OUT_OF_MEMORY),
2174 : : errmsg("out of memory")));
2175 : 1650 : }
2176 : :
2177 : : /*
2178 : : * It is sufficient to get shared lock on ProcArrayLock, even if we are
2179 : : * going to set MyProc->xmin.
2180 : : */
2181 : 705687 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2182 : :
2183 [ + + ]: 705687 : if (GetSnapshotDataReuse(snapshot))
2184 : : {
2185 : 620223 : LWLockRelease(ProcArrayLock);
2186 : 620223 : return snapshot;
2187 : : }
2188 : :
2189 : 85464 : latest_completed = TransamVariables->latestCompletedXid;
2190 : 85464 : mypgxactoff = MyProc->pgxactoff;
2191 : 85464 : myxid = other_xids[mypgxactoff];
2192 [ + - ]: 85464 : Assert(myxid == MyProc->xid);
2193 : :
2194 : 85464 : oldestxid = TransamVariables->oldestXid;
2195 : 85464 : curXactCompletionCount = TransamVariables->xactCompletionCount;
2196 : :
2197 : : /* xmax is always latestCompletedXid + 1 */
2198 : 85464 : xmax = XidFromFullTransactionId(latest_completed);
2199 [ + - ]: 85464 : TransactionIdAdvance(xmax);
2200 [ + - ]: 85464 : Assert(TransactionIdIsNormal(xmax));
2201 : :
2202 : : /* initialize xmin calculation with xmax */
2203 : 85464 : xmin = xmax;
2204 : :
2205 : : /* take own xid into account, saves a check inside the loop */
2206 [ + + + - : 85464 : if (TransactionIdIsNormal(myxid) && NormalTransactionIdPrecedes(myxid, xmin))
+ + ]
2207 : 9476 : xmin = myxid;
2208 : :
2209 : 85464 : snapshot->takenDuringRecovery = RecoveryInProgress();
2210 : :
2211 [ - + ]: 85464 : if (!snapshot->takenDuringRecovery)
2212 : : {
2213 : 85464 : int numProcs = arrayP->numProcs;
2214 : 85464 : TransactionId *xip = snapshot->xip;
2215 : 85464 : int *pgprocnos = arrayP->pgprocnos;
2216 : 85464 : XidCacheStatus *subxidStates = ProcGlobal->subxidStates;
2217 : 85464 : uint8 *allStatusFlags = ProcGlobal->statusFlags;
2218 : :
2219 : : /*
2220 : : * First collect set of pgxactoff/xids that need to be included in the
2221 : : * snapshot.
2222 : : */
2223 [ + + ]: 978371 : for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
2224 : : {
2225 : : /* Fetch xid just once - see GetNewTransactionId */
2226 : 892907 : TransactionId xid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
2227 : 892907 : uint8 statusFlags;
2228 : :
2229 [ + - ]: 892907 : Assert(allProcs[arrayP->pgprocnos[pgxactoff]].pgxactoff == pgxactoff);
2230 : :
2231 : : /*
2232 : : * If the transaction has no XID assigned, we can skip it; it
2233 : : * won't have sub-XIDs either.
2234 : : */
2235 [ + + ]: 892907 : if (likely(xid == InvalidTransactionId))
2236 : 719340 : continue;
2237 : :
2238 : : /*
2239 : : * We don't include our own XIDs (if any) in the snapshot. It
2240 : : * needs to be included in the xmin computation, but we did so
2241 : : * outside the loop.
2242 : : */
2243 [ + + ]: 173567 : if (pgxactoff == mypgxactoff)
2244 : 14969 : continue;
2245 : :
2246 : : /*
2247 : : * The only way we are able to get here with a non-normal xid is
2248 : : * during bootstrap - with this backend using
2249 : : * BootstrapTransactionId. But the above test should filter that
2250 : : * out.
2251 : : */
2252 [ + - ]: 158598 : Assert(TransactionIdIsNormal(xid));
2253 : :
2254 : : /*
2255 : : * If the XID is >= xmax, we can skip it; such transactions will
2256 : : * be treated as running anyway (and any sub-XIDs will also be >=
2257 : : * xmax).
2258 : : */
2259 [ + - + + ]: 158598 : if (!NormalTransactionIdPrecedes(xid, xmax))
2260 : 33852 : continue;
2261 : :
2262 : : /*
2263 : : * Skip over backends doing logical decoding which manages xmin
2264 : : * separately (check below) and ones running LAZY VACUUM.
2265 : : */
2266 : 124746 : statusFlags = allStatusFlags[pgxactoff];
2267 [ - + ]: 124746 : if (statusFlags & (PROC_IN_LOGICAL_DECODING | PROC_IN_VACUUM))
2268 : 0 : continue;
2269 : :
2270 [ + - + + ]: 124746 : if (NormalTransactionIdPrecedes(xid, xmin))
2271 : 81711 : xmin = xid;
2272 : :
2273 : : /* Add XID to snapshot. */
2274 : 124746 : xip[count++] = xid;
2275 : :
2276 : : /*
2277 : : * Save subtransaction XIDs if possible (if we've already
2278 : : * overflowed, there's no point). Note that the subxact XIDs must
2279 : : * be later than their parent, so no need to check them against
2280 : : * xmin. We could filter against xmax, but it seems better not to
2281 : : * do that much work while holding the ProcArrayLock.
2282 : : *
2283 : : * The other backend can add more subxids concurrently, but cannot
2284 : : * remove any. Hence it's important to fetch nxids just once.
2285 : : * Should be safe to use memcpy, though. (We needn't worry about
2286 : : * missing any xids added concurrently, because they must postdate
2287 : : * xmax.)
2288 : : *
2289 : : * Again, our own XIDs are not included in the snapshot.
2290 : : */
2291 [ - + ]: 124746 : if (!suboverflowed)
2292 : : {
2293 : :
2294 [ - + ]: 124746 : if (subxidStates[pgxactoff].overflowed)
2295 : 0 : suboverflowed = true;
2296 : : else
2297 : : {
2298 : 124746 : int nsubxids = subxidStates[pgxactoff].count;
2299 : :
2300 [ + + ]: 124746 : if (nsubxids > 0)
2301 : : {
2302 : 1519 : int pgprocno = pgprocnos[pgxactoff];
2303 : 1519 : PGPROC *proc = &allProcs[pgprocno];
2304 : :
2305 : 1519 : pg_read_barrier(); /* pairs with GetNewTransactionId */
2306 : :
2307 : 1519 : memcpy(snapshot->subxip + subcount,
2308 : : proc->subxids.xids,
2309 : : nsubxids * sizeof(TransactionId));
2310 : 1519 : subcount += nsubxids;
2311 : 1519 : }
2312 : 124746 : }
2313 : 124746 : }
2314 [ - + + ]: 892907 : }
2315 : 85464 : }
2316 : : else
2317 : : {
2318 : : /*
2319 : : * We're in hot standby, so get XIDs from KnownAssignedXids.
2320 : : *
2321 : : * We store all xids directly into subxip[]. Here's why:
2322 : : *
2323 : : * In recovery we don't know which xids are top-level and which are
2324 : : * subxacts, a design choice that greatly simplifies xid processing.
2325 : : *
2326 : : * It seems like we would want to try to put xids into xip[] only, but
2327 : : * that is fairly small. We would either need to make that bigger or
2328 : : * to increase the rate at which we WAL-log xid assignment; neither is
2329 : : * an appealing choice.
2330 : : *
2331 : : * We could try to store xids into xip[] first and then into subxip[]
2332 : : * if there are too many xids. That only works if the snapshot doesn't
2333 : : * overflow because we do not search subxip[] in that case. A simpler
2334 : : * way is to just store all xids in the subxip array because this is
2335 : : * by far the bigger array. We just leave the xip array empty.
2336 : : *
2337 : : * Either way we need to change the way XidInMVCCSnapshot() works
2338 : : * depending upon when the snapshot was taken, or change normal
2339 : : * snapshot processing so it matches.
2340 : : *
2341 : : * Note: It is possible for recovery to end before we finish taking
2342 : : * the snapshot, and for newly assigned transaction ids to be added to
2343 : : * the ProcArray. xmax cannot change while we hold ProcArrayLock, so
2344 : : * those newly added transaction ids would be filtered away, so we
2345 : : * need not be concerned about them.
2346 : : */
2347 : 0 : subcount = KnownAssignedXidsGetAndSetXmin(snapshot->subxip, &xmin,
2348 : 0 : xmax);
2349 : :
2350 [ # # ]: 0 : if (TransactionIdPrecedesOrEquals(xmin, procArray->lastOverflowedXid))
2351 : 0 : suboverflowed = true;
2352 : : }
2353 : :
2354 : :
2355 : : /*
2356 : : * Fetch into local variable while ProcArrayLock is held - the
2357 : : * LWLockRelease below is a barrier, ensuring this happens inside the
2358 : : * lock.
2359 : : */
2360 : 85464 : replication_slot_xmin = procArray->replication_slot_xmin;
2361 : 85464 : replication_slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
2362 : :
2363 [ + + ]: 85464 : if (!TransactionIdIsValid(MyProc->xmin))
2364 : 42665 : MyProc->xmin = TransactionXmin = xmin;
2365 : :
2366 : 85464 : LWLockRelease(ProcArrayLock);
2367 : :
2368 : : /* maintain state for GlobalVis* */
2369 : : {
2370 : 85464 : TransactionId def_vis_xid;
2371 : 85464 : TransactionId def_vis_xid_data;
2372 : 85464 : FullTransactionId def_vis_fxid;
2373 : 85464 : FullTransactionId def_vis_fxid_data;
2374 : 85464 : FullTransactionId oldestfxid;
2375 : :
2376 : : /*
2377 : : * Converting oldestXid is only safe when xid horizon cannot advance,
2378 : : * i.e. holding locks. While we don't hold the lock anymore, all the
2379 : : * necessary data has been gathered with lock held.
2380 : : */
2381 : 85464 : oldestfxid = FullXidRelativeTo(latest_completed, oldestxid);
2382 : :
2383 : : /* Check whether there's a replication slot requiring an older xmin. */
2384 : 85464 : def_vis_xid_data =
2385 : 85464 : TransactionIdOlder(xmin, replication_slot_xmin);
2386 : :
2387 : : /*
2388 : : * Rows in non-shared, non-catalog tables possibly could be vacuumed
2389 : : * if older than this xid.
2390 : : */
2391 : 85464 : def_vis_xid = def_vis_xid_data;
2392 : :
2393 : : /*
2394 : : * Check whether there's a replication slot requiring an older catalog
2395 : : * xmin.
2396 : : */
2397 : 85464 : def_vis_xid =
2398 : 85464 : TransactionIdOlder(replication_slot_catalog_xmin, def_vis_xid);
2399 : :
2400 : 85464 : def_vis_fxid = FullXidRelativeTo(latest_completed, def_vis_xid);
2401 : 85464 : def_vis_fxid_data = FullXidRelativeTo(latest_completed, def_vis_xid_data);
2402 : :
2403 : : /*
2404 : : * Check if we can increase upper bound. As a previous
2405 : : * GlobalVisUpdate() might have computed more aggressive values, don't
2406 : : * overwrite them if so.
2407 : : */
2408 : : GlobalVisSharedRels.definitely_needed =
2409 : 85464 : FullTransactionIdNewer(def_vis_fxid,
2410 : : GlobalVisSharedRels.definitely_needed);
2411 : : GlobalVisCatalogRels.definitely_needed =
2412 : 85464 : FullTransactionIdNewer(def_vis_fxid,
2413 : : GlobalVisCatalogRels.definitely_needed);
2414 : : GlobalVisDataRels.definitely_needed =
2415 : 85464 : FullTransactionIdNewer(def_vis_fxid_data,
2416 : : GlobalVisDataRels.definitely_needed);
2417 : : /* See temp_oldest_nonremovable computation in ComputeXidHorizons() */
2418 [ + + ]: 85464 : if (TransactionIdIsNormal(myxid))
2419 : 14967 : GlobalVisTempRels.definitely_needed =
2420 : 14967 : FullXidRelativeTo(latest_completed, myxid);
2421 : : else
2422 : : {
2423 : 70497 : GlobalVisTempRels.definitely_needed = latest_completed;
2424 : 70497 : FullTransactionIdAdvance(&GlobalVisTempRels.definitely_needed);
2425 : : }
2426 : :
2427 : : /*
2428 : : * Check if we know that we can initialize or increase the lower
2429 : : * bound. Currently the only cheap way to do so is to use
2430 : : * TransamVariables->oldestXid as input.
2431 : : *
2432 : : * We should definitely be able to do better. We could e.g. put a
2433 : : * global lower bound value into TransamVariables.
2434 : : */
2435 : : GlobalVisSharedRels.maybe_needed =
2436 : 85464 : FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
2437 : : oldestfxid);
2438 : : GlobalVisCatalogRels.maybe_needed =
2439 : 85464 : FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
2440 : : oldestfxid);
2441 : : GlobalVisDataRels.maybe_needed =
2442 : 85464 : FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
2443 : : oldestfxid);
2444 : : /* accurate value known */
2445 : 85464 : GlobalVisTempRels.maybe_needed = GlobalVisTempRels.definitely_needed;
2446 : 85464 : }
2447 : :
2448 : 85464 : RecentXmin = xmin;
2449 [ + - ]: 85464 : Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
2450 : :
2451 : 85464 : snapshot->xmin = xmin;
2452 : 85464 : snapshot->xmax = xmax;
2453 : 85464 : snapshot->xcnt = count;
2454 : 85464 : snapshot->subxcnt = subcount;
2455 : 85464 : snapshot->suboverflowed = suboverflowed;
2456 : 85464 : snapshot->snapXactCompletionCount = curXactCompletionCount;
2457 : :
2458 : 85464 : snapshot->curcid = GetCurrentCommandId(false);
2459 : :
2460 : : /*
2461 : : * This is a new snapshot, so set both refcounts are zero, and mark it as
2462 : : * not copied in persistent memory.
2463 : : */
2464 : 85464 : snapshot->active_count = 0;
2465 : 85464 : snapshot->regd_count = 0;
2466 : 85464 : snapshot->copied = false;
2467 : :
2468 : 85464 : return snapshot;
2469 : 705687 : }
2470 : :
2471 : : /*
2472 : : * ProcArrayInstallImportedXmin -- install imported xmin into MyProc->xmin
2473 : : *
2474 : : * This is called when installing a snapshot imported from another
2475 : : * transaction. To ensure that OldestXmin doesn't go backwards, we must
2476 : : * check that the source transaction is still running, and we'd better do
2477 : : * that atomically with installing the new xmin.
2478 : : *
2479 : : * Returns true if successful, false if source xact is no longer running.
2480 : : */
2481 : : bool
2482 : 0 : ProcArrayInstallImportedXmin(TransactionId xmin,
2483 : : VirtualTransactionId *sourcevxid)
2484 : : {
2485 : 0 : bool result = false;
2486 : 0 : ProcArrayStruct *arrayP = procArray;
2487 : 0 : int index;
2488 : :
2489 [ # # ]: 0 : Assert(TransactionIdIsNormal(xmin));
2490 [ # # ]: 0 : if (!sourcevxid)
2491 : 0 : return false;
2492 : :
2493 : : /* Get lock so source xact can't end while we're doing this */
2494 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2495 : :
2496 : : /*
2497 : : * Find the PGPROC entry of the source transaction. (This could use
2498 : : * GetPGProcByNumber(), unless it's a prepared xact. But this isn't
2499 : : * performance critical.)
2500 : : */
2501 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
2502 : : {
2503 : 0 : int pgprocno = arrayP->pgprocnos[index];
2504 : 0 : PGPROC *proc = &allProcs[pgprocno];
2505 : 0 : int statusFlags = ProcGlobal->statusFlags[index];
2506 : 0 : TransactionId xid;
2507 : :
2508 : : /* Ignore procs running LAZY VACUUM */
2509 [ # # ]: 0 : if (statusFlags & PROC_IN_VACUUM)
2510 : 0 : continue;
2511 : :
2512 : : /* We are only interested in the specific virtual transaction. */
2513 [ # # ]: 0 : if (proc->vxid.procNumber != sourcevxid->procNumber)
2514 : 0 : continue;
2515 [ # # ]: 0 : if (proc->vxid.lxid != sourcevxid->localTransactionId)
2516 : 0 : continue;
2517 : :
2518 : : /*
2519 : : * We check the transaction's database ID for paranoia's sake: if it's
2520 : : * in another DB then its xmin does not cover us. Caller should have
2521 : : * detected this already, so we just treat any funny cases as
2522 : : * "transaction not found".
2523 : : */
2524 [ # # ]: 0 : if (proc->databaseId != MyDatabaseId)
2525 : 0 : continue;
2526 : :
2527 : : /*
2528 : : * Likewise, let's just make real sure its xmin does cover us.
2529 : : */
2530 : 0 : xid = UINT32_ACCESS_ONCE(proc->xmin);
2531 [ # # # # ]: 0 : if (!TransactionIdIsNormal(xid) ||
2532 : 0 : !TransactionIdPrecedesOrEquals(xid, xmin))
2533 : 0 : continue;
2534 : :
2535 : : /*
2536 : : * We're good. Install the new xmin. As in GetSnapshotData, set
2537 : : * TransactionXmin too. (Note that because snapmgr.c called
2538 : : * GetSnapshotData first, we'll be overwriting a valid xmin here, so
2539 : : * we don't check that.)
2540 : : */
2541 : 0 : MyProc->xmin = TransactionXmin = xmin;
2542 : :
2543 : 0 : result = true;
2544 : 0 : break;
2545 [ # # # ]: 0 : }
2546 : :
2547 : 0 : LWLockRelease(ProcArrayLock);
2548 : :
2549 : 0 : return result;
2550 : 0 : }
2551 : :
2552 : : /*
2553 : : * ProcArrayInstallRestoredXmin -- install restored xmin into MyProc->xmin
2554 : : *
2555 : : * This is like ProcArrayInstallImportedXmin, but we have a pointer to the
2556 : : * PGPROC of the transaction from which we imported the snapshot, rather than
2557 : : * an XID.
2558 : : *
2559 : : * Note that this function also copies statusFlags from the source `proc` in
2560 : : * order to avoid the case where MyProc's xmin needs to be skipped for
2561 : : * computing xid horizon.
2562 : : *
2563 : : * Returns true if successful, false if source xact is no longer running.
2564 : : */
2565 : : bool
2566 : 477 : ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
2567 : : {
2568 : 477 : bool result = false;
2569 : 477 : TransactionId xid;
2570 : :
2571 [ + - ]: 477 : Assert(TransactionIdIsNormal(xmin));
2572 [ + - ]: 477 : Assert(proc != NULL);
2573 : :
2574 : : /*
2575 : : * Get an exclusive lock so that we can copy statusFlags from source proc.
2576 : : */
2577 : 477 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
2578 : :
2579 : : /*
2580 : : * Be certain that the referenced PGPROC has an advertised xmin which is
2581 : : * no later than the one we're installing, so that the system-wide xmin
2582 : : * can't go backwards. Also, make sure it's running in the same database,
2583 : : * so that the per-database xmin cannot go backwards.
2584 : : */
2585 : 477 : xid = UINT32_ACCESS_ONCE(proc->xmin);
2586 [ + - ]: 477 : if (proc->databaseId == MyDatabaseId &&
2587 [ + - - + ]: 477 : TransactionIdIsNormal(xid) &&
2588 : 477 : TransactionIdPrecedesOrEquals(xid, xmin))
2589 : : {
2590 : : /*
2591 : : * Install xmin and propagate the statusFlags that affect how the
2592 : : * value is interpreted by vacuum.
2593 : : */
2594 : 477 : MyProc->xmin = TransactionXmin = xmin;
2595 : 954 : MyProc->statusFlags = (MyProc->statusFlags & ~PROC_XMIN_FLAGS) |
2596 : 477 : (proc->statusFlags & PROC_XMIN_FLAGS);
2597 : 477 : ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
2598 : :
2599 : 477 : result = true;
2600 : 477 : }
2601 : :
2602 : 477 : LWLockRelease(ProcArrayLock);
2603 : :
2604 : 954 : return result;
2605 : 477 : }
2606 : :
2607 : : /*
2608 : : * GetRunningTransactionData -- returns information about running transactions.
2609 : : *
2610 : : * Similar to GetSnapshotData but returns more information. We include
2611 : : * all PGPROCs with an assigned TransactionId, even VACUUM processes and
2612 : : * prepared transactions.
2613 : : *
2614 : : * We acquire XidGenLock and ProcArrayLock, but the caller is responsible for
2615 : : * releasing them. Acquiring XidGenLock ensures that no new XIDs enter the proc
2616 : : * array until the caller has WAL-logged this snapshot, and releases the
2617 : : * lock. Acquiring ProcArrayLock ensures that no transactions commit until the
2618 : : * lock is released.
2619 : : *
2620 : : * The returned data structure is statically allocated; caller should not
2621 : : * modify it, and must not assume it is valid past the next call.
2622 : : *
2623 : : * This is never executed during recovery so there is no need to look at
2624 : : * KnownAssignedXids.
2625 : : *
2626 : : * Dummy PGPROCs from prepared transaction are included, meaning that this
2627 : : * may return entries with duplicated TransactionId values coming from
2628 : : * transaction finishing to prepare. Nothing is done about duplicated
2629 : : * entries here to not hold on ProcArrayLock more than necessary.
2630 : : *
2631 : : * We don't worry about updating other counters, we want to keep this as
2632 : : * simple as possible and leave GetSnapshotData() as the primary code for
2633 : : * that bookkeeping.
2634 : : *
2635 : : * Note that if any transaction has overflowed its cached subtransactions
2636 : : * then there is no real need include any subtransactions.
2637 : : */
2638 : : RunningTransactions
2639 : 4 : GetRunningTransactionData(void)
2640 : : {
2641 : : /* result workspace */
2642 : : static RunningTransactionsData CurrentRunningXactsData;
2643 : :
2644 : 4 : ProcArrayStruct *arrayP = procArray;
2645 : 4 : TransactionId *other_xids = ProcGlobal->xids;
2646 : 4 : RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
2647 : 4 : TransactionId latestCompletedXid;
2648 : 4 : TransactionId oldestRunningXid;
2649 : 4 : TransactionId oldestDatabaseRunningXid;
2650 : 4 : TransactionId *xids;
2651 : 4 : int index;
2652 : 4 : int count;
2653 : 4 : int subcount;
2654 : 4 : bool suboverflowed;
2655 : :
2656 [ + - ]: 4 : Assert(!RecoveryInProgress());
2657 : :
2658 : : /*
2659 : : * Allocating space for maxProcs xids is usually overkill; numProcs would
2660 : : * be sufficient. But it seems better to do the malloc while not holding
2661 : : * the lock, so we can't look at numProcs. Likewise, we allocate much
2662 : : * more subxip storage than is probably needed.
2663 : : *
2664 : : * Should only be allocated in bgwriter, since only ever executed during
2665 : : * checkpoints.
2666 : : */
2667 [ + + ]: 4 : if (CurrentRunningXacts->xids == NULL)
2668 : : {
2669 : : /*
2670 : : * First call
2671 : : */
2672 : 1 : CurrentRunningXacts->xids = (TransactionId *)
2673 : 1 : malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
2674 [ + - ]: 1 : if (CurrentRunningXacts->xids == NULL)
2675 [ # # # # ]: 0 : ereport(ERROR,
2676 : : (errcode(ERRCODE_OUT_OF_MEMORY),
2677 : : errmsg("out of memory")));
2678 : 1 : }
2679 : :
2680 : 4 : xids = CurrentRunningXacts->xids;
2681 : :
2682 : 4 : count = subcount = 0;
2683 : 4 : suboverflowed = false;
2684 : :
2685 : : /*
2686 : : * Ensure that no xids enter or leave the procarray while we obtain
2687 : : * snapshot.
2688 : : */
2689 : 4 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2690 : 4 : LWLockAcquire(XidGenLock, LW_SHARED);
2691 : :
2692 : 4 : latestCompletedXid =
2693 : 4 : XidFromFullTransactionId(TransamVariables->latestCompletedXid);
2694 : 4 : oldestDatabaseRunningXid = oldestRunningXid =
2695 : 4 : XidFromFullTransactionId(TransamVariables->nextXid);
2696 : :
2697 : : /*
2698 : : * Spin over procArray collecting all xids
2699 : : */
2700 [ + + ]: 8 : for (index = 0; index < arrayP->numProcs; index++)
2701 : : {
2702 : 4 : TransactionId xid;
2703 : :
2704 : : /* Fetch xid just once - see GetNewTransactionId */
2705 : 4 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2706 : :
2707 : : /*
2708 : : * We don't need to store transactions that don't have a TransactionId
2709 : : * yet because they will not show as running on a standby server.
2710 : : */
2711 [ + - ]: 4 : if (!TransactionIdIsValid(xid))
2712 : 0 : continue;
2713 : :
2714 : : /*
2715 : : * Be careful not to exclude any xids before calculating the values of
2716 : : * oldestRunningXid and suboverflowed, since these are used to clean
2717 : : * up transaction information held on standbys.
2718 : : */
2719 [ - + ]: 4 : if (TransactionIdPrecedes(xid, oldestRunningXid))
2720 : 4 : oldestRunningXid = xid;
2721 : :
2722 : : /*
2723 : : * Also, update the oldest running xid within the current database. As
2724 : : * fetching pgprocno and PGPROC could cause cache misses, we do cheap
2725 : : * TransactionId comparison first.
2726 : : */
2727 [ - + ]: 4 : if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
2728 : : {
2729 : 4 : int pgprocno = arrayP->pgprocnos[index];
2730 : 4 : PGPROC *proc = &allProcs[pgprocno];
2731 : :
2732 [ - + ]: 4 : if (proc->databaseId == MyDatabaseId)
2733 : 4 : oldestDatabaseRunningXid = xid;
2734 : 4 : }
2735 : :
2736 [ + - ]: 4 : if (ProcGlobal->subxidStates[index].overflowed)
2737 : 0 : suboverflowed = true;
2738 : :
2739 : : /*
2740 : : * If we wished to exclude xids this would be the right place for it.
2741 : : * Procs with the PROC_IN_VACUUM flag set don't usually assign xids,
2742 : : * but they do during truncation at the end when they get the lock and
2743 : : * truncate, so it is not much of a problem to include them if they
2744 : : * are seen and it is cleaner to include them.
2745 : : */
2746 : :
2747 : 4 : xids[count++] = xid;
2748 [ - - + ]: 4 : }
2749 : :
2750 : : /*
2751 : : * Spin over procArray collecting all subxids, but only if there hasn't
2752 : : * been a suboverflow.
2753 : : */
2754 [ - + ]: 4 : if (!suboverflowed)
2755 : : {
2756 : 4 : XidCacheStatus *other_subxidstates = ProcGlobal->subxidStates;
2757 : :
2758 [ + + ]: 8 : for (index = 0; index < arrayP->numProcs; index++)
2759 : : {
2760 : 4 : int pgprocno = arrayP->pgprocnos[index];
2761 : 4 : PGPROC *proc = &allProcs[pgprocno];
2762 : 4 : int nsubxids;
2763 : :
2764 : : /*
2765 : : * Save subtransaction XIDs. Other backends can't add or remove
2766 : : * entries while we're holding XidGenLock.
2767 : : */
2768 : 4 : nsubxids = other_subxidstates[index].count;
2769 [ + - ]: 4 : if (nsubxids > 0)
2770 : : {
2771 : : /* barrier not really required, as XidGenLock is held, but ... */
2772 : 0 : pg_read_barrier(); /* pairs with GetNewTransactionId */
2773 : :
2774 : 0 : memcpy(&xids[count], proc->subxids.xids,
2775 : : nsubxids * sizeof(TransactionId));
2776 : 0 : count += nsubxids;
2777 : 0 : subcount += nsubxids;
2778 : :
2779 : : /*
2780 : : * Top-level XID of a transaction is always less than any of
2781 : : * its subxids, so we don't need to check if any of the
2782 : : * subxids are smaller than oldestRunningXid
2783 : : */
2784 : 0 : }
2785 : 4 : }
2786 : 4 : }
2787 : :
2788 : : /*
2789 : : * It's important *not* to include the limits set by slots here because
2790 : : * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
2791 : : * were to be included here the initial value could never increase because
2792 : : * of a circular dependency where slots only increase their limits when
2793 : : * running xacts increases oldestRunningXid and running xacts only
2794 : : * increases if slots do.
2795 : : */
2796 : :
2797 : 4 : CurrentRunningXacts->xcnt = count - subcount;
2798 : 4 : CurrentRunningXacts->subxcnt = subcount;
2799 : 4 : CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
2800 : 4 : CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
2801 : 4 : CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
2802 : 4 : CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
2803 : 4 : CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
2804 : :
2805 [ + - ]: 4 : Assert(TransactionIdIsValid(CurrentRunningXacts->nextXid));
2806 [ + - ]: 4 : Assert(TransactionIdIsValid(CurrentRunningXacts->oldestRunningXid));
2807 [ + - ]: 4 : Assert(TransactionIdIsNormal(CurrentRunningXacts->latestCompletedXid));
2808 : :
2809 : : /* We don't release the locks here, the caller is responsible for that */
2810 : :
2811 : 8 : return CurrentRunningXacts;
2812 : 4 : }
2813 : :
2814 : : /*
2815 : : * GetOldestActiveTransactionId()
2816 : : *
2817 : : * Similar to GetSnapshotData but returns just oldestActiveXid. We include
2818 : : * all PGPROCs with an assigned TransactionId, even VACUUM processes.
2819 : : *
2820 : : * If allDbs is true, we look at all databases, though there is no need to
2821 : : * include WALSender since this has no effect on hot standby conflicts. If
2822 : : * allDbs is false, skip processes attached to other databases.
2823 : : *
2824 : : * This is never executed during recovery so there is no need to look at
2825 : : * KnownAssignedXids.
2826 : : *
2827 : : * We don't worry about updating other counters, we want to keep this as
2828 : : * simple as possible and leave GetSnapshotData() as the primary code for
2829 : : * that bookkeeping.
2830 : : *
2831 : : * inCommitOnly indicates getting the oldestActiveXid among the transactions
2832 : : * in the commit critical section.
2833 : : */
2834 : : TransactionId
2835 : 4 : GetOldestActiveTransactionId(bool inCommitOnly, bool allDbs)
2836 : : {
2837 : 4 : ProcArrayStruct *arrayP = procArray;
2838 : 4 : TransactionId *other_xids = ProcGlobal->xids;
2839 : 4 : TransactionId oldestRunningXid;
2840 : 4 : int index;
2841 : :
2842 [ + - ]: 4 : Assert(!RecoveryInProgress());
2843 : :
2844 : : /*
2845 : : * Read nextXid, as the upper bound of what's still active.
2846 : : *
2847 : : * Reading a TransactionId is atomic, but we must grab the lock to make
2848 : : * sure that all XIDs < nextXid are already present in the proc array (or
2849 : : * have already completed), when we spin over it.
2850 : : */
2851 : 4 : LWLockAcquire(XidGenLock, LW_SHARED);
2852 : 4 : oldestRunningXid = XidFromFullTransactionId(TransamVariables->nextXid);
2853 : 4 : LWLockRelease(XidGenLock);
2854 : :
2855 : : /*
2856 : : * Spin over procArray collecting all xids and subxids.
2857 : : */
2858 : 4 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2859 [ + + ]: 8 : for (index = 0; index < arrayP->numProcs; index++)
2860 : : {
2861 : 4 : TransactionId xid;
2862 : 4 : int pgprocno = arrayP->pgprocnos[index];
2863 : 4 : PGPROC *proc = &allProcs[pgprocno];
2864 : :
2865 : : /* Fetch xid just once - see GetNewTransactionId */
2866 : 4 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2867 : :
2868 [ + - ]: 4 : if (!TransactionIdIsNormal(xid))
2869 : 0 : continue;
2870 : :
2871 [ - + # # ]: 4 : if (inCommitOnly &&
2872 : 0 : (proc->delayChkptFlags & DELAY_CHKPT_IN_COMMIT) == 0)
2873 : 0 : continue;
2874 : :
2875 [ - + # # ]: 4 : if (!allDbs && proc->databaseId != MyDatabaseId)
2876 : 0 : continue;
2877 : :
2878 [ - + ]: 4 : if (TransactionIdPrecedes(xid, oldestRunningXid))
2879 : 4 : oldestRunningXid = xid;
2880 : :
2881 : : /*
2882 : : * Top-level XID of a transaction is always less than any of its
2883 : : * subxids, so we don't need to check if any of the subxids are
2884 : : * smaller than oldestRunningXid
2885 : : */
2886 [ - - + ]: 4 : }
2887 : 4 : LWLockRelease(ProcArrayLock);
2888 : :
2889 : 8 : return oldestRunningXid;
2890 : 4 : }
2891 : :
2892 : : /*
2893 : : * GetOldestSafeDecodingTransactionId -- lowest xid not affected by vacuum
2894 : : *
2895 : : * Returns the oldest xid that we can guarantee not to have been affected by
2896 : : * vacuum, i.e. no rows >= that xid have been vacuumed away unless the
2897 : : * transaction aborted. Note that the value can (and most of the time will) be
2898 : : * much more conservative than what really has been affected by vacuum, but we
2899 : : * currently don't have better data available.
2900 : : *
2901 : : * This is useful to initialize the cutoff xid after which a new changeset
2902 : : * extraction replication slot can start decoding changes.
2903 : : *
2904 : : * Must be called with ProcArrayLock held either shared or exclusively,
2905 : : * although most callers will want to use exclusive mode since it is expected
2906 : : * that the caller will immediately use the xid to peg the xmin horizon.
2907 : : */
2908 : : TransactionId
2909 : 0 : GetOldestSafeDecodingTransactionId(bool catalogOnly)
2910 : : {
2911 : 0 : ProcArrayStruct *arrayP = procArray;
2912 : 0 : TransactionId oldestSafeXid;
2913 : 0 : int index;
2914 : 0 : bool recovery_in_progress = RecoveryInProgress();
2915 : :
2916 [ # # ]: 0 : Assert(LWLockHeldByMe(ProcArrayLock));
2917 : :
2918 : : /*
2919 : : * Acquire XidGenLock, so no transactions can acquire an xid while we're
2920 : : * running. If no transaction with xid were running concurrently a new xid
2921 : : * could influence the RecentXmin et al.
2922 : : *
2923 : : * We initialize the computation to nextXid since that's guaranteed to be
2924 : : * a safe, albeit pessimal, value.
2925 : : */
2926 : 0 : LWLockAcquire(XidGenLock, LW_SHARED);
2927 : 0 : oldestSafeXid = XidFromFullTransactionId(TransamVariables->nextXid);
2928 : :
2929 : : /*
2930 : : * If there's already a slot pegging the xmin horizon, we can start with
2931 : : * that value, it's guaranteed to be safe since it's computed by this
2932 : : * routine initially and has been enforced since. We can always use the
2933 : : * slot's general xmin horizon, but the catalog horizon is only usable
2934 : : * when only catalog data is going to be looked at.
2935 : : */
2936 [ # # # # ]: 0 : if (TransactionIdIsValid(procArray->replication_slot_xmin) &&
2937 : 0 : TransactionIdPrecedes(procArray->replication_slot_xmin,
2938 : 0 : oldestSafeXid))
2939 : 0 : oldestSafeXid = procArray->replication_slot_xmin;
2940 : :
2941 [ # # ]: 0 : if (catalogOnly &&
2942 [ # # # # ]: 0 : TransactionIdIsValid(procArray->replication_slot_catalog_xmin) &&
2943 : 0 : TransactionIdPrecedes(procArray->replication_slot_catalog_xmin,
2944 : 0 : oldestSafeXid))
2945 : 0 : oldestSafeXid = procArray->replication_slot_catalog_xmin;
2946 : :
2947 : : /*
2948 : : * If we're not in recovery, we walk over the procarray and collect the
2949 : : * lowest xid. Since we're called with ProcArrayLock held and have
2950 : : * acquired XidGenLock, no entries can vanish concurrently, since
2951 : : * ProcGlobal->xids[i] is only set with XidGenLock held and only cleared
2952 : : * with ProcArrayLock held.
2953 : : *
2954 : : * In recovery we can't lower the safe value besides what we've computed
2955 : : * above, so we'll have to wait a bit longer there. We unfortunately can
2956 : : * *not* use KnownAssignedXidsGetOldestXmin() since the KnownAssignedXids
2957 : : * machinery can miss values and return an older value than is safe.
2958 : : */
2959 [ # # ]: 0 : if (!recovery_in_progress)
2960 : : {
2961 : 0 : TransactionId *other_xids = ProcGlobal->xids;
2962 : :
2963 : : /*
2964 : : * Spin over procArray collecting min(ProcGlobal->xids[i])
2965 : : */
2966 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
2967 : : {
2968 : 0 : TransactionId xid;
2969 : :
2970 : : /* Fetch xid just once - see GetNewTransactionId */
2971 : 0 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2972 : :
2973 [ # # ]: 0 : if (!TransactionIdIsNormal(xid))
2974 : 0 : continue;
2975 : :
2976 [ # # ]: 0 : if (TransactionIdPrecedes(xid, oldestSafeXid))
2977 : 0 : oldestSafeXid = xid;
2978 [ # # # ]: 0 : }
2979 : 0 : }
2980 : :
2981 : 0 : LWLockRelease(XidGenLock);
2982 : :
2983 : 0 : return oldestSafeXid;
2984 : 0 : }
2985 : :
2986 : : /*
2987 : : * GetVirtualXIDsDelayingChkpt -- Get the VXIDs of transactions that are
2988 : : * delaying checkpoint because they have critical actions in progress.
2989 : : *
2990 : : * Constructs an array of VXIDs of transactions that are currently in commit
2991 : : * critical sections, as shown by having specified delayChkptFlags bits set
2992 : : * in their PGPROC.
2993 : : *
2994 : : * Returns a palloc'd array that should be freed by the caller.
2995 : : * *nvxids is the number of valid entries.
2996 : : *
2997 : : * Note that because backends set or clear delayChkptFlags without holding any
2998 : : * lock, the result is somewhat indeterminate, but we don't really care. Even
2999 : : * in a multiprocessor with delayed writes to shared memory, it should be
3000 : : * certain that setting of delayChkptFlags will propagate to shared memory
3001 : : * when the backend takes a lock, so we cannot fail to see a virtual xact as
3002 : : * delayChkptFlags if it's already inserted its commit record. Whether it
3003 : : * takes a little while for clearing of delayChkptFlags to propagate is
3004 : : * unimportant for correctness.
3005 : : */
3006 : : VirtualTransactionId *
3007 : 14 : GetVirtualXIDsDelayingChkpt(int *nvxids, int type)
3008 : : {
3009 : 14 : VirtualTransactionId *vxids;
3010 : 14 : ProcArrayStruct *arrayP = procArray;
3011 : 14 : int count = 0;
3012 : 14 : int index;
3013 : :
3014 [ + - ]: 14 : Assert(type != 0);
3015 : :
3016 : : /* allocate what's certainly enough result space */
3017 : 14 : vxids = palloc_array(VirtualTransactionId, arrayP->maxProcs);
3018 : :
3019 : 14 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3020 : :
3021 [ + + ]: 26 : for (index = 0; index < arrayP->numProcs; index++)
3022 : : {
3023 : 12 : int pgprocno = arrayP->pgprocnos[index];
3024 : 12 : PGPROC *proc = &allProcs[pgprocno];
3025 : :
3026 [ + - ]: 12 : if ((proc->delayChkptFlags & type) != 0)
3027 : : {
3028 : 0 : VirtualTransactionId vxid;
3029 : :
3030 : 0 : GET_VXID_FROM_PGPROC(vxid, *proc);
3031 [ # # ]: 0 : if (VirtualTransactionIdIsValid(vxid))
3032 : 0 : vxids[count++] = vxid;
3033 : 0 : }
3034 : 12 : }
3035 : :
3036 : 14 : LWLockRelease(ProcArrayLock);
3037 : :
3038 : 14 : *nvxids = count;
3039 : 28 : return vxids;
3040 : 14 : }
3041 : :
3042 : : /*
3043 : : * HaveVirtualXIDsDelayingChkpt -- Are any of the specified VXIDs delaying?
3044 : : *
3045 : : * This is used with the results of GetVirtualXIDsDelayingChkpt to see if any
3046 : : * of the specified VXIDs are still in critical sections of code.
3047 : : *
3048 : : * Note: this is O(N^2) in the number of vxacts that are/were delaying, but
3049 : : * those numbers should be small enough for it not to be a problem.
3050 : : */
3051 : : bool
3052 : 0 : HaveVirtualXIDsDelayingChkpt(VirtualTransactionId *vxids, int nvxids, int type)
3053 : : {
3054 : 0 : bool result = false;
3055 : 0 : ProcArrayStruct *arrayP = procArray;
3056 : 0 : int index;
3057 : :
3058 [ # # ]: 0 : Assert(type != 0);
3059 : :
3060 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3061 : :
3062 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3063 : : {
3064 : 0 : int pgprocno = arrayP->pgprocnos[index];
3065 : 0 : PGPROC *proc = &allProcs[pgprocno];
3066 : 0 : VirtualTransactionId vxid;
3067 : :
3068 : 0 : GET_VXID_FROM_PGPROC(vxid, *proc);
3069 : :
3070 [ # # # # ]: 0 : if ((proc->delayChkptFlags & type) != 0 &&
3071 : 0 : VirtualTransactionIdIsValid(vxid))
3072 : : {
3073 : 0 : int i;
3074 : :
3075 [ # # ]: 0 : for (i = 0; i < nvxids; i++)
3076 : : {
3077 [ # # # # ]: 0 : if (VirtualTransactionIdEquals(vxid, vxids[i]))
3078 : : {
3079 : 0 : result = true;
3080 : 0 : break;
3081 : : }
3082 : 0 : }
3083 [ # # ]: 0 : if (result)
3084 : 0 : break;
3085 [ # # ]: 0 : }
3086 [ # # # ]: 0 : }
3087 : :
3088 : 0 : LWLockRelease(ProcArrayLock);
3089 : :
3090 : 0 : return result;
3091 : 0 : }
3092 : :
3093 : : /*
3094 : : * ProcNumberGetProc -- get a backend's PGPROC given its proc number
3095 : : *
3096 : : * The result may be out of date arbitrarily quickly, so the caller
3097 : : * must be careful about how this information is used. NULL is
3098 : : * returned if the backend is not active.
3099 : : */
3100 : : PGPROC *
3101 : 48 : ProcNumberGetProc(ProcNumber procNumber)
3102 : : {
3103 : 48 : PGPROC *result;
3104 : :
3105 [ + - - + ]: 48 : if (procNumber < 0 || procNumber >= ProcGlobal->allProcCount)
3106 : 0 : return NULL;
3107 : 48 : result = GetPGProcByNumber(procNumber);
3108 : :
3109 [ + - ]: 48 : if (result->pid == 0)
3110 : 0 : return NULL;
3111 : :
3112 : 48 : return result;
3113 : 48 : }
3114 : :
3115 : : /*
3116 : : * ProcNumberGetTransactionIds -- get a backend's transaction status
3117 : : *
3118 : : * Get the xid, xmin, nsubxid and overflow status of the backend. The
3119 : : * result may be out of date arbitrarily quickly, so the caller must be
3120 : : * careful about how this information is used.
3121 : : */
3122 : : void
3123 : 276 : ProcNumberGetTransactionIds(ProcNumber procNumber, TransactionId *xid,
3124 : : TransactionId *xmin, int *nsubxid, bool *overflowed)
3125 : : {
3126 : 276 : PGPROC *proc;
3127 : :
3128 : 276 : *xid = InvalidTransactionId;
3129 : 276 : *xmin = InvalidTransactionId;
3130 : 276 : *nsubxid = 0;
3131 : 276 : *overflowed = false;
3132 : :
3133 [ + - - + ]: 276 : if (procNumber < 0 || procNumber >= ProcGlobal->allProcCount)
3134 : 0 : return;
3135 : 276 : proc = GetPGProcByNumber(procNumber);
3136 : :
3137 : : /* Need to lock out additions/removals of backends */
3138 : 276 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3139 : :
3140 [ - + ]: 276 : if (proc->pid != 0)
3141 : : {
3142 : 276 : *xid = proc->xid;
3143 : 276 : *xmin = proc->xmin;
3144 : 276 : *nsubxid = proc->subxidStatus.count;
3145 : 276 : *overflowed = proc->subxidStatus.overflowed;
3146 : 276 : }
3147 : :
3148 : 276 : LWLockRelease(ProcArrayLock);
3149 [ - + ]: 276 : }
3150 : :
3151 : : /*
3152 : : * BackendPidGetProc -- get a backend's PGPROC given its PID
3153 : : *
3154 : : * Returns NULL if not found. Note that it is up to the caller to be
3155 : : * sure that the question remains meaningful for long enough for the
3156 : : * answer to be used ...
3157 : : */
3158 : : PGPROC *
3159 : 105 : BackendPidGetProc(int pid)
3160 : : {
3161 : 105 : PGPROC *result;
3162 : :
3163 [ + + ]: 105 : if (pid == 0) /* never match dummy PGPROCs */
3164 : 1 : return NULL;
3165 : :
3166 : 104 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3167 : :
3168 : 104 : result = BackendPidGetProcWithLock(pid);
3169 : :
3170 : 104 : LWLockRelease(ProcArrayLock);
3171 : :
3172 : 104 : return result;
3173 : 105 : }
3174 : :
3175 : : /*
3176 : : * BackendPidGetProcWithLock -- get a backend's PGPROC given its PID
3177 : : *
3178 : : * Same as above, except caller must be holding ProcArrayLock. The found
3179 : : * entry, if any, can be assumed to be valid as long as the lock remains held.
3180 : : */
3181 : : PGPROC *
3182 : 104 : BackendPidGetProcWithLock(int pid)
3183 : : {
3184 : 104 : PGPROC *result = NULL;
3185 : 104 : ProcArrayStruct *arrayP = procArray;
3186 : 104 : int index;
3187 : :
3188 [ - + ]: 104 : if (pid == 0) /* never match dummy PGPROCs */
3189 : 0 : return NULL;
3190 : :
3191 [ + + ]: 820 : for (index = 0; index < arrayP->numProcs; index++)
3192 : : {
3193 : 782 : PGPROC *proc = &allProcs[arrayP->pgprocnos[index]];
3194 : :
3195 [ + + ]: 782 : if (proc->pid == pid)
3196 : : {
3197 : 66 : result = proc;
3198 : 66 : break;
3199 : : }
3200 [ - + + ]: 782 : }
3201 : :
3202 : 104 : return result;
3203 : 104 : }
3204 : :
3205 : : /*
3206 : : * BackendXidGetPid -- get a backend's pid given its XID
3207 : : *
3208 : : * Returns 0 if not found or it's a prepared transaction. Note that
3209 : : * it is up to the caller to be sure that the question remains
3210 : : * meaningful for long enough for the answer to be used ...
3211 : : *
3212 : : * Only main transaction Ids are considered. This function is mainly
3213 : : * useful for determining what backend owns a lock.
3214 : : *
3215 : : * Beware that not every xact has an XID assigned. However, as long as you
3216 : : * only call this using an XID found on disk, you're safe.
3217 : : */
3218 : : int
3219 : 0 : BackendXidGetPid(TransactionId xid)
3220 : : {
3221 : 0 : int result = 0;
3222 : 0 : ProcArrayStruct *arrayP = procArray;
3223 : 0 : TransactionId *other_xids = ProcGlobal->xids;
3224 : 0 : int index;
3225 : :
3226 [ # # ]: 0 : if (xid == InvalidTransactionId) /* never match invalid xid */
3227 : 0 : return 0;
3228 : :
3229 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3230 : :
3231 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3232 : : {
3233 [ # # ]: 0 : if (other_xids[index] == xid)
3234 : : {
3235 : 0 : int pgprocno = arrayP->pgprocnos[index];
3236 : 0 : PGPROC *proc = &allProcs[pgprocno];
3237 : :
3238 : 0 : result = proc->pid;
3239 : : break;
3240 : 0 : }
3241 : 0 : }
3242 : :
3243 : 0 : LWLockRelease(ProcArrayLock);
3244 : :
3245 : 0 : return result;
3246 : 0 : }
3247 : :
3248 : : /*
3249 : : * IsBackendPid -- is a given pid a running backend
3250 : : *
3251 : : * This is not called by the backend, but is called by external modules.
3252 : : */
3253 : : bool
3254 : 0 : IsBackendPid(int pid)
3255 : : {
3256 : 0 : return (BackendPidGetProc(pid) != NULL);
3257 : : }
3258 : :
3259 : :
3260 : : /*
3261 : : * GetCurrentVirtualXIDs -- returns an array of currently active VXIDs.
3262 : : *
3263 : : * The array is palloc'd. The number of valid entries is returned into *nvxids.
3264 : : *
3265 : : * The arguments allow filtering the set of VXIDs returned. Our own process
3266 : : * is always skipped. In addition:
3267 : : * If limitXmin is not InvalidTransactionId, skip processes with
3268 : : * xmin > limitXmin.
3269 : : * If excludeXmin0 is true, skip processes with xmin = 0.
3270 : : * If allDbs is false, skip processes attached to other databases.
3271 : : * If excludeVacuum isn't zero, skip processes for which
3272 : : * (statusFlags & excludeVacuum) is not zero.
3273 : : *
3274 : : * Note: the purpose of the limitXmin and excludeXmin0 parameters is to
3275 : : * allow skipping backends whose oldest live snapshot is no older than
3276 : : * some snapshot we have. Since we examine the procarray with only shared
3277 : : * lock, there are race conditions: a backend could set its xmin just after
3278 : : * we look. Indeed, on multiprocessors with weak memory ordering, the
3279 : : * other backend could have set its xmin *before* we look. We know however
3280 : : * that such a backend must have held shared ProcArrayLock overlapping our
3281 : : * own hold of ProcArrayLock, else we would see its xmin update. Therefore,
3282 : : * any snapshot the other backend is taking concurrently with our scan cannot
3283 : : * consider any transactions as still running that we think are committed
3284 : : * (since backends must hold ProcArrayLock exclusive to commit).
3285 : : */
3286 : : VirtualTransactionId *
3287 : 71 : GetCurrentVirtualXIDs(TransactionId limitXmin, bool excludeXmin0,
3288 : : bool allDbs, int excludeVacuum,
3289 : : int *nvxids)
3290 : : {
3291 : 71 : VirtualTransactionId *vxids;
3292 : 71 : ProcArrayStruct *arrayP = procArray;
3293 : 71 : int count = 0;
3294 : 71 : int index;
3295 : :
3296 : : /* allocate what's certainly enough result space */
3297 : 71 : vxids = palloc_array(VirtualTransactionId, arrayP->maxProcs);
3298 : :
3299 : 71 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3300 : :
3301 [ + + ]: 389 : for (index = 0; index < arrayP->numProcs; index++)
3302 : : {
3303 : 318 : int pgprocno = arrayP->pgprocnos[index];
3304 : 318 : PGPROC *proc = &allProcs[pgprocno];
3305 : 318 : uint8 statusFlags = ProcGlobal->statusFlags[index];
3306 : :
3307 [ + + ]: 318 : if (proc == MyProc)
3308 : 71 : continue;
3309 : :
3310 [ + + ]: 247 : if (excludeVacuum & statusFlags)
3311 : 2 : continue;
3312 : :
3313 [ + - + + ]: 245 : if (allDbs || proc->databaseId == MyDatabaseId)
3314 : : {
3315 : : /* Fetch xmin just once - might change on us */
3316 : 103 : TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
3317 : :
3318 [ + - + + ]: 103 : if (excludeXmin0 && !TransactionIdIsValid(pxmin))
3319 : 39 : continue;
3320 : :
3321 : : /*
3322 : : * InvalidTransactionId precedes all other XIDs, so a proc that
3323 : : * hasn't set xmin yet will not be rejected by this test.
3324 : : */
3325 [ + - + + ]: 64 : if (!TransactionIdIsValid(limitXmin) ||
3326 : 64 : TransactionIdPrecedesOrEquals(pxmin, limitXmin))
3327 : : {
3328 : 61 : VirtualTransactionId vxid;
3329 : :
3330 : 61 : GET_VXID_FROM_PGPROC(vxid, *proc);
3331 [ - + ]: 61 : if (VirtualTransactionIdIsValid(vxid))
3332 : 61 : vxids[count++] = vxid;
3333 : 61 : }
3334 [ + + ]: 103 : }
3335 [ - + + ]: 318 : }
3336 : :
3337 : 71 : LWLockRelease(ProcArrayLock);
3338 : :
3339 : 71 : *nvxids = count;
3340 : 142 : return vxids;
3341 : 71 : }
3342 : :
3343 : : /*
3344 : : * GetConflictingVirtualXIDs -- returns an array of currently active VXIDs.
3345 : : *
3346 : : * Usage is limited to conflict resolution during recovery on standby servers.
3347 : : * limitXmin is supplied as either a cutoff with snapshotConflictHorizon
3348 : : * semantics, or InvalidTransactionId in cases where caller cannot accurately
3349 : : * determine a safe snapshotConflictHorizon value.
3350 : : *
3351 : : * If limitXmin is InvalidTransactionId then we want to kill everybody,
3352 : : * so we're not worried if they have a snapshot or not, nor does it really
3353 : : * matter what type of lock we hold. Caller must avoid calling here with
3354 : : * snapshotConflictHorizon style cutoffs that were set to InvalidTransactionId
3355 : : * during original execution, since that actually indicates that there is
3356 : : * definitely no need for a recovery conflict (the snapshotConflictHorizon
3357 : : * convention for InvalidTransactionId values is the opposite of our own!).
3358 : : *
3359 : : * All callers that are checking xmins always now supply a valid and useful
3360 : : * value for limitXmin. The limitXmin is always lower than the lowest
3361 : : * numbered KnownAssignedXid that is not already a FATAL error. This is
3362 : : * because we only care about cleanup records that are cleaning up tuple
3363 : : * versions from committed transactions. In that case they will only occur
3364 : : * at the point where the record is less than the lowest running xid. That
3365 : : * allows us to say that if any backend takes a snapshot concurrently with
3366 : : * us then the conflict assessment made here would never include the snapshot
3367 : : * that is being derived. So we take LW_SHARED on the ProcArray and allow
3368 : : * concurrent snapshots when limitXmin is valid. We might think about adding
3369 : : * Assert(limitXmin < lowest(KnownAssignedXids))
3370 : : * but that would not be true in the case of FATAL errors lagging in array,
3371 : : * but we already know those are bogus anyway, so we skip that test.
3372 : : *
3373 : : * If dbOid is valid we skip backends attached to other databases.
3374 : : *
3375 : : * Be careful to *not* pfree the result from this function. We reuse
3376 : : * this array sufficiently often that we use malloc for the result.
3377 : : */
3378 : : VirtualTransactionId *
3379 : 0 : GetConflictingVirtualXIDs(TransactionId limitXmin, Oid dbOid)
3380 : : {
3381 : : static VirtualTransactionId *vxids;
3382 : 0 : ProcArrayStruct *arrayP = procArray;
3383 : 0 : int count = 0;
3384 : 0 : int index;
3385 : :
3386 : : /*
3387 : : * If first time through, get workspace to remember main XIDs in. We
3388 : : * malloc it permanently to avoid repeated palloc/pfree overhead. Allow
3389 : : * result space, remembering room for a terminator.
3390 : : */
3391 [ # # ]: 0 : if (vxids == NULL)
3392 : : {
3393 : 0 : vxids = (VirtualTransactionId *)
3394 : 0 : malloc(sizeof(VirtualTransactionId) * (arrayP->maxProcs + 1));
3395 [ # # ]: 0 : if (vxids == NULL)
3396 [ # # # # ]: 0 : ereport(ERROR,
3397 : : (errcode(ERRCODE_OUT_OF_MEMORY),
3398 : : errmsg("out of memory")));
3399 : 0 : }
3400 : :
3401 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3402 : :
3403 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3404 : : {
3405 : 0 : int pgprocno = arrayP->pgprocnos[index];
3406 : 0 : PGPROC *proc = &allProcs[pgprocno];
3407 : :
3408 : : /* Exclude prepared transactions */
3409 [ # # ]: 0 : if (proc->pid == 0)
3410 : 0 : continue;
3411 : :
3412 [ # # # # ]: 0 : if (!OidIsValid(dbOid) ||
3413 : 0 : proc->databaseId == dbOid)
3414 : : {
3415 : : /* Fetch xmin just once - can't change on us, but good coding */
3416 : 0 : TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
3417 : :
3418 : : /*
3419 : : * We ignore an invalid pxmin because this means that backend has
3420 : : * no snapshot currently. We hold a Share lock to avoid contention
3421 : : * with users taking snapshots. That is not a problem because the
3422 : : * current xmin is always at least one higher than the latest
3423 : : * removed xid, so any new snapshot would never conflict with the
3424 : : * test here.
3425 : : */
3426 [ # # # # ]: 0 : if (!TransactionIdIsValid(limitXmin) ||
3427 [ # # ]: 0 : (TransactionIdIsValid(pxmin) && !TransactionIdFollows(pxmin, limitXmin)))
3428 : : {
3429 : 0 : VirtualTransactionId vxid;
3430 : :
3431 : 0 : GET_VXID_FROM_PGPROC(vxid, *proc);
3432 [ # # ]: 0 : if (VirtualTransactionIdIsValid(vxid))
3433 : 0 : vxids[count++] = vxid;
3434 : 0 : }
3435 : 0 : }
3436 [ # # # ]: 0 : }
3437 : :
3438 : 0 : LWLockRelease(ProcArrayLock);
3439 : :
3440 : : /* add the terminator */
3441 : 0 : vxids[count].procNumber = INVALID_PROC_NUMBER;
3442 : 0 : vxids[count].localTransactionId = InvalidLocalTransactionId;
3443 : :
3444 : 0 : return vxids;
3445 : 0 : }
3446 : :
3447 : : /*
3448 : : * CancelVirtualTransaction - used in recovery conflict processing
3449 : : *
3450 : : * Returns pid of the process signaled, or 0 if not found.
3451 : : */
3452 : : pid_t
3453 : 0 : CancelVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode)
3454 : : {
3455 : 0 : return SignalVirtualTransaction(vxid, sigmode, true);
3456 : : }
3457 : :
3458 : : pid_t
3459 : 0 : SignalVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode,
3460 : : bool conflictPending)
3461 : : {
3462 : 0 : ProcArrayStruct *arrayP = procArray;
3463 : 0 : int index;
3464 : 0 : pid_t pid = 0;
3465 : :
3466 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3467 : :
3468 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3469 : : {
3470 : 0 : int pgprocno = arrayP->pgprocnos[index];
3471 : 0 : PGPROC *proc = &allProcs[pgprocno];
3472 : 0 : VirtualTransactionId procvxid;
3473 : :
3474 : 0 : GET_VXID_FROM_PGPROC(procvxid, *proc);
3475 : :
3476 [ # # # # ]: 0 : if (procvxid.procNumber == vxid.procNumber &&
3477 : 0 : procvxid.localTransactionId == vxid.localTransactionId)
3478 : : {
3479 : 0 : proc->recoveryConflictPending = conflictPending;
3480 : 0 : pid = proc->pid;
3481 [ # # ]: 0 : if (pid != 0)
3482 : : {
3483 : : /*
3484 : : * Kill the pid if it's still here. If not, that's what we
3485 : : * wanted so ignore any errors.
3486 : : */
3487 : 0 : (void) SendProcSignal(pid, sigmode, vxid.procNumber);
3488 : 0 : }
3489 : 0 : break;
3490 : : }
3491 [ # # # ]: 0 : }
3492 : :
3493 : 0 : LWLockRelease(ProcArrayLock);
3494 : :
3495 : 0 : return pid;
3496 : 0 : }
3497 : :
3498 : : /*
3499 : : * MinimumActiveBackends --- count backends (other than myself) that are
3500 : : * in active transactions. Return true if the count exceeds the
3501 : : * minimum threshold passed. This is used as a heuristic to decide if
3502 : : * a pre-XLOG-flush delay is worthwhile during commit.
3503 : : *
3504 : : * Do not count backends that are blocked waiting for locks, since they are
3505 : : * not going to get to run until someone else commits.
3506 : : */
3507 : : bool
3508 : 0 : MinimumActiveBackends(int min)
3509 : : {
3510 : 0 : ProcArrayStruct *arrayP = procArray;
3511 : 0 : int count = 0;
3512 : 0 : int index;
3513 : :
3514 : : /* Quick short-circuit if no minimum is specified */
3515 [ # # ]: 0 : if (min == 0)
3516 : 0 : return true;
3517 : :
3518 : : /*
3519 : : * Note: for speed, we don't acquire ProcArrayLock. This is a little bit
3520 : : * bogus, but since we are only testing fields for zero or nonzero, it
3521 : : * should be OK. The result is only used for heuristic purposes anyway...
3522 : : */
3523 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3524 : : {
3525 : 0 : int pgprocno = arrayP->pgprocnos[index];
3526 : 0 : PGPROC *proc = &allProcs[pgprocno];
3527 : :
3528 : : /*
3529 : : * Since we're not holding a lock, need to be prepared to deal with
3530 : : * garbage, as someone could have incremented numProcs but not yet
3531 : : * filled the structure.
3532 : : *
3533 : : * If someone just decremented numProcs, 'proc' could also point to a
3534 : : * PGPROC entry that's no longer in the array. It still points to a
3535 : : * PGPROC struct, though, because freed PGPROC entries just go to the
3536 : : * free list and are recycled. Its contents are nonsense in that case,
3537 : : * but that's acceptable for this function.
3538 : : */
3539 [ # # ]: 0 : if (pgprocno == -1)
3540 : 0 : continue; /* do not count deleted entries */
3541 [ # # ]: 0 : if (proc == MyProc)
3542 : 0 : continue; /* do not count myself */
3543 [ # # ]: 0 : if (proc->xid == InvalidTransactionId)
3544 : 0 : continue; /* do not count if no XID assigned */
3545 [ # # ]: 0 : if (proc->pid == 0)
3546 : 0 : continue; /* do not count prepared xacts */
3547 [ # # ]: 0 : if (proc->waitLock != NULL)
3548 : 0 : continue; /* do not count if blocked on a lock */
3549 : 0 : count++;
3550 [ # # ]: 0 : if (count >= min)
3551 : 0 : break;
3552 [ # # # # ]: 0 : }
3553 : :
3554 : 0 : return count >= min;
3555 : 0 : }
3556 : :
3557 : : /*
3558 : : * CountDBBackends --- count backends that are using specified database
3559 : : */
3560 : : int
3561 : 0 : CountDBBackends(Oid databaseid)
3562 : : {
3563 : 0 : ProcArrayStruct *arrayP = procArray;
3564 : 0 : int count = 0;
3565 : 0 : int index;
3566 : :
3567 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3568 : :
3569 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3570 : : {
3571 : 0 : int pgprocno = arrayP->pgprocnos[index];
3572 : 0 : PGPROC *proc = &allProcs[pgprocno];
3573 : :
3574 [ # # ]: 0 : if (proc->pid == 0)
3575 : 0 : continue; /* do not count prepared xacts */
3576 [ # # # # ]: 0 : if (!OidIsValid(databaseid) ||
3577 : 0 : proc->databaseId == databaseid)
3578 : 0 : count++;
3579 [ # # # ]: 0 : }
3580 : :
3581 : 0 : LWLockRelease(ProcArrayLock);
3582 : :
3583 : 0 : return count;
3584 : 0 : }
3585 : :
3586 : : /*
3587 : : * CountDBConnections --- counts database backends (only regular backends)
3588 : : */
3589 : : int
3590 : 0 : CountDBConnections(Oid databaseid)
3591 : : {
3592 : 0 : ProcArrayStruct *arrayP = procArray;
3593 : 0 : int count = 0;
3594 : 0 : int index;
3595 : :
3596 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3597 : :
3598 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3599 : : {
3600 : 0 : int pgprocno = arrayP->pgprocnos[index];
3601 : 0 : PGPROC *proc = &allProcs[pgprocno];
3602 : :
3603 [ # # ]: 0 : if (proc->pid == 0)
3604 : 0 : continue; /* do not count prepared xacts */
3605 [ # # ]: 0 : if (!proc->isRegularBackend)
3606 : 0 : continue; /* count only regular backend processes */
3607 [ # # # # ]: 0 : if (!OidIsValid(databaseid) ||
3608 : 0 : proc->databaseId == databaseid)
3609 : 0 : count++;
3610 [ # # # ]: 0 : }
3611 : :
3612 : 0 : LWLockRelease(ProcArrayLock);
3613 : :
3614 : 0 : return count;
3615 : 0 : }
3616 : :
3617 : : /*
3618 : : * CancelDBBackends --- cancel backends that are using specified database
3619 : : */
3620 : : void
3621 : 0 : CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conflictPending)
3622 : : {
3623 : 0 : ProcArrayStruct *arrayP = procArray;
3624 : 0 : int index;
3625 : :
3626 : : /* tell all backends to die */
3627 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3628 : :
3629 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3630 : : {
3631 : 0 : int pgprocno = arrayP->pgprocnos[index];
3632 : 0 : PGPROC *proc = &allProcs[pgprocno];
3633 : :
3634 [ # # # # ]: 0 : if (databaseid == InvalidOid || proc->databaseId == databaseid)
3635 : : {
3636 : 0 : VirtualTransactionId procvxid;
3637 : 0 : pid_t pid;
3638 : :
3639 : 0 : GET_VXID_FROM_PGPROC(procvxid, *proc);
3640 : :
3641 : 0 : proc->recoveryConflictPending = conflictPending;
3642 : 0 : pid = proc->pid;
3643 [ # # ]: 0 : if (pid != 0)
3644 : : {
3645 : : /*
3646 : : * Kill the pid if it's still here. If not, that's what we
3647 : : * wanted so ignore any errors.
3648 : : */
3649 : 0 : (void) SendProcSignal(pid, sigmode, procvxid.procNumber);
3650 : 0 : }
3651 : 0 : }
3652 : 0 : }
3653 : :
3654 : 0 : LWLockRelease(ProcArrayLock);
3655 : 0 : }
3656 : :
3657 : : /*
3658 : : * CountUserBackends --- count backends that are used by specified user
3659 : : * (only regular backends, not any type of background worker)
3660 : : */
3661 : : int
3662 : 0 : CountUserBackends(Oid roleid)
3663 : : {
3664 : 0 : ProcArrayStruct *arrayP = procArray;
3665 : 0 : int count = 0;
3666 : 0 : int index;
3667 : :
3668 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3669 : :
3670 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3671 : : {
3672 : 0 : int pgprocno = arrayP->pgprocnos[index];
3673 : 0 : PGPROC *proc = &allProcs[pgprocno];
3674 : :
3675 [ # # ]: 0 : if (proc->pid == 0)
3676 : 0 : continue; /* do not count prepared xacts */
3677 [ # # ]: 0 : if (!proc->isRegularBackend)
3678 : 0 : continue; /* count only regular backend processes */
3679 [ # # ]: 0 : if (proc->roleId == roleid)
3680 : 0 : count++;
3681 [ # # # ]: 0 : }
3682 : :
3683 : 0 : LWLockRelease(ProcArrayLock);
3684 : :
3685 : 0 : return count;
3686 : 0 : }
3687 : :
3688 : : /*
3689 : : * CountOtherDBBackends -- check for other backends running in the given DB
3690 : : *
3691 : : * If there are other backends in the DB, we will wait a maximum of 5 seconds
3692 : : * for them to exit (or 0.3s for testing purposes). Autovacuum backends are
3693 : : * encouraged to exit early by sending them SIGTERM, but normal user backends
3694 : : * are just waited for. If background workers connected to this database are
3695 : : * marked as interruptible, they are terminated.
3696 : : *
3697 : : * The current backend is always ignored; it is caller's responsibility to
3698 : : * check whether the current backend uses the given DB, if it's important.
3699 : : *
3700 : : * Returns true if there are (still) other backends in the DB, false if not.
3701 : : * Also, *nbackends and *nprepared are set to the number of other backends
3702 : : * and prepared transactions in the DB, respectively.
3703 : : *
3704 : : * This function is used to interlock DROP DATABASE and related commands
3705 : : * against there being any active backends in the target DB --- dropping the
3706 : : * DB while active backends remain would be a Bad Thing. Note that we cannot
3707 : : * detect here the possibility of a newly-started backend that is trying to
3708 : : * connect to the doomed database, so additional interlocking is needed during
3709 : : * backend startup. The caller should normally hold an exclusive lock on the
3710 : : * target DB before calling this, which is one reason we mustn't wait
3711 : : * indefinitely.
3712 : : */
3713 : : bool
3714 : 10 : CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
3715 : : {
3716 : 10 : ProcArrayStruct *arrayP = procArray;
3717 : :
3718 : : #define MAXAUTOVACPIDS 10 /* max autovacs to SIGTERM per iteration */
3719 : 10 : int autovac_pids[MAXAUTOVACPIDS];
3720 : :
3721 : : /*
3722 : : * Retry up to 50 times with 100ms between attempts (max 5s total). Can be
3723 : : * reduced to 3 attempts (max 0.3s total) to speed up tests.
3724 : : */
3725 : 10 : int ntries = 50;
3726 : :
3727 : : #ifdef USE_INJECTION_POINTS
3728 : : if (IS_INJECTION_POINT_ATTACHED("procarray-reduce-count"))
3729 : : ntries = 3;
3730 : : #endif
3731 : :
3732 [ + - + - ]: 20 : for (int tries = 0; tries < ntries; tries++)
3733 : : {
3734 : 10 : int nautovacs = 0;
3735 : 10 : bool found = false;
3736 : 10 : int index;
3737 : :
3738 [ - + ]: 10 : CHECK_FOR_INTERRUPTS();
3739 : :
3740 : 10 : *nbackends = *nprepared = 0;
3741 : :
3742 : 10 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3743 : :
3744 [ + + ]: 55 : for (index = 0; index < arrayP->numProcs; index++)
3745 : : {
3746 : 45 : int pgprocno = arrayP->pgprocnos[index];
3747 : 45 : PGPROC *proc = &allProcs[pgprocno];
3748 : 45 : uint8 statusFlags = ProcGlobal->statusFlags[index];
3749 : :
3750 [ + + ]: 45 : if (proc->databaseId != databaseId)
3751 : 43 : continue;
3752 [ - + ]: 2 : if (proc == MyProc)
3753 : 2 : continue;
3754 : :
3755 : 0 : found = true;
3756 : :
3757 [ # # ]: 0 : if (proc->pid == 0)
3758 : 0 : (*nprepared)++;
3759 : : else
3760 : : {
3761 : 0 : (*nbackends)++;
3762 [ # # # # ]: 0 : if ((statusFlags & PROC_IS_AUTOVACUUM) &&
3763 : 0 : nautovacs < MAXAUTOVACPIDS)
3764 : 0 : autovac_pids[nautovacs++] = proc->pid;
3765 : : }
3766 [ - + - ]: 45 : }
3767 : :
3768 : 10 : LWLockRelease(ProcArrayLock);
3769 : :
3770 [ - + ]: 10 : if (!found)
3771 : 10 : return false; /* no conflicting backends, so done */
3772 : :
3773 : : /*
3774 : : * Send SIGTERM to any conflicting autovacuums before sleeping. We
3775 : : * postpone this step until after the loop because we don't want to
3776 : : * hold ProcArrayLock while issuing kill(). We have no idea what might
3777 : : * block kill() inside the kernel...
3778 : : */
3779 [ # # ]: 0 : for (index = 0; index < nautovacs; index++)
3780 : 0 : (void) kill(autovac_pids[index], SIGTERM); /* ignore any error */
3781 : :
3782 : : /*
3783 : : * Terminate all background workers for this database, if they have
3784 : : * requested it (BGWORKER_INTERRUPTIBLE).
3785 : : */
3786 : 0 : TerminateBackgroundWorkersForDatabase(databaseId);
3787 : :
3788 : : /* sleep, then try again */
3789 : 0 : pg_usleep(100 * 1000L); /* 100ms */
3790 [ + - ]: 10 : }
3791 : :
3792 : 0 : return true; /* timed out, still conflicts */
3793 : 10 : }
3794 : :
3795 : : /*
3796 : : * Terminate existing connections to the specified database. This routine
3797 : : * is used by the DROP DATABASE command when user has asked to forcefully
3798 : : * drop the database.
3799 : : *
3800 : : * The current backend is always ignored; it is caller's responsibility to
3801 : : * check whether the current backend uses the given DB, if it's important.
3802 : : *
3803 : : * If the target database has a prepared transaction or permissions checks
3804 : : * fail for a connection, this fails without terminating anything.
3805 : : */
3806 : : void
3807 : 0 : TerminateOtherDBBackends(Oid databaseId)
3808 : : {
3809 : 0 : ProcArrayStruct *arrayP = procArray;
3810 : 0 : List *pids = NIL;
3811 : 0 : int nprepared = 0;
3812 : 0 : int i;
3813 : :
3814 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3815 : :
3816 [ # # ]: 0 : for (i = 0; i < procArray->numProcs; i++)
3817 : : {
3818 : 0 : int pgprocno = arrayP->pgprocnos[i];
3819 : 0 : PGPROC *proc = &allProcs[pgprocno];
3820 : :
3821 [ # # ]: 0 : if (proc->databaseId != databaseId)
3822 : 0 : continue;
3823 [ # # ]: 0 : if (proc == MyProc)
3824 : 0 : continue;
3825 : :
3826 [ # # ]: 0 : if (proc->pid != 0)
3827 : 0 : pids = lappend_int(pids, proc->pid);
3828 : : else
3829 : 0 : nprepared++;
3830 [ # # # ]: 0 : }
3831 : :
3832 : 0 : LWLockRelease(ProcArrayLock);
3833 : :
3834 [ # # ]: 0 : if (nprepared > 0)
3835 [ # # # # ]: 0 : ereport(ERROR,
3836 : : (errcode(ERRCODE_OBJECT_IN_USE),
3837 : : errmsg("database \"%s\" is being used by prepared transactions",
3838 : : get_database_name(databaseId)),
3839 : : errdetail_plural("There is %d prepared transaction using the database.",
3840 : : "There are %d prepared transactions using the database.",
3841 : : nprepared,
3842 : : nprepared)));
3843 : :
3844 [ # # ]: 0 : if (pids)
3845 : : {
3846 : 0 : ListCell *lc;
3847 : :
3848 : : /*
3849 : : * Permissions checks relax the pg_terminate_backend checks in two
3850 : : * ways, both by omitting the !OidIsValid(proc->roleId) check:
3851 : : *
3852 : : * - Accept terminating autovacuum workers, since DROP DATABASE
3853 : : * without FORCE terminates them.
3854 : : *
3855 : : * - Accept terminating bgworkers. For bgworker authors, it's
3856 : : * convenient to be able to recommend FORCE if a worker is blocking
3857 : : * DROP DATABASE unexpectedly.
3858 : : *
3859 : : * Unlike pg_terminate_backend, we don't raise some warnings - like
3860 : : * "PID %d is not a PostgreSQL server process", because for us already
3861 : : * finished session is not a problem.
3862 : : */
3863 [ # # # # : 0 : foreach(lc, pids)
# # ]
3864 : : {
3865 : 0 : int pid = lfirst_int(lc);
3866 : 0 : PGPROC *proc = BackendPidGetProc(pid);
3867 : :
3868 [ # # ]: 0 : if (proc != NULL)
3869 : : {
3870 [ # # # # ]: 0 : if (superuser_arg(proc->roleId) && !superuser())
3871 [ # # # # ]: 0 : ereport(ERROR,
3872 : : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
3873 : : errmsg("permission denied to terminate process"),
3874 : : errdetail("Only roles with the %s attribute may terminate processes of roles with the %s attribute.",
3875 : : "SUPERUSER", "SUPERUSER")));
3876 : :
3877 [ # # # # ]: 0 : if (!has_privs_of_role(GetUserId(), proc->roleId) &&
3878 : 0 : !has_privs_of_role(GetUserId(), ROLE_PG_SIGNAL_BACKEND))
3879 [ # # # # ]: 0 : ereport(ERROR,
3880 : : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
3881 : : errmsg("permission denied to terminate process"),
3882 : : errdetail("Only roles with privileges of the role whose process is being terminated or with privileges of the \"%s\" role may terminate this process.",
3883 : : "pg_signal_backend")));
3884 : 0 : }
3885 : 0 : }
3886 : :
3887 : : /*
3888 : : * There's a race condition here: once we release the ProcArrayLock,
3889 : : * it's possible for the session to exit before we issue kill. That
3890 : : * race condition possibility seems too unlikely to worry about. See
3891 : : * pg_signal_backend.
3892 : : */
3893 [ # # # # : 0 : foreach(lc, pids)
# # ]
3894 : : {
3895 : 0 : int pid = lfirst_int(lc);
3896 : 0 : PGPROC *proc = BackendPidGetProc(pid);
3897 : :
3898 [ # # ]: 0 : if (proc != NULL)
3899 : : {
3900 : : /*
3901 : : * If we have setsid(), signal the backend's whole process
3902 : : * group
3903 : : */
3904 : : #ifdef HAVE_SETSID
3905 : 0 : (void) kill(-pid, SIGTERM);
3906 : : #else
3907 : : (void) kill(pid, SIGTERM);
3908 : : #endif
3909 : 0 : }
3910 : 0 : }
3911 : 0 : }
3912 : 0 : }
3913 : :
3914 : : /*
3915 : : * ProcArraySetReplicationSlotXmin
3916 : : *
3917 : : * Install limits to future computations of the xmin horizon to prevent vacuum
3918 : : * and HOT pruning from removing affected rows still needed by clients with
3919 : : * replication slots.
3920 : : */
3921 : : void
3922 : 4 : ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,
3923 : : bool already_locked)
3924 : : {
3925 [ - + # # ]: 4 : Assert(!already_locked || LWLockHeldByMe(ProcArrayLock));
3926 : :
3927 [ - + ]: 4 : if (!already_locked)
3928 : 4 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3929 : :
3930 : 4 : procArray->replication_slot_xmin = xmin;
3931 : 4 : procArray->replication_slot_catalog_xmin = catalog_xmin;
3932 : :
3933 [ - + ]: 4 : if (!already_locked)
3934 : 4 : LWLockRelease(ProcArrayLock);
3935 : :
3936 [ - + - + ]: 4 : elog(DEBUG1, "xmin required by slots: data %u, catalog %u",
3937 : : xmin, catalog_xmin);
3938 : 4 : }
3939 : :
3940 : : /*
3941 : : * ProcArrayGetReplicationSlotXmin
3942 : : *
3943 : : * Return the current slot xmin limits. That's useful to be able to remove
3944 : : * data that's older than those limits.
3945 : : */
3946 : : void
3947 : 0 : ProcArrayGetReplicationSlotXmin(TransactionId *xmin,
3948 : : TransactionId *catalog_xmin)
3949 : : {
3950 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3951 : :
3952 [ # # ]: 0 : if (xmin != NULL)
3953 : 0 : *xmin = procArray->replication_slot_xmin;
3954 : :
3955 [ # # ]: 0 : if (catalog_xmin != NULL)
3956 : 0 : *catalog_xmin = procArray->replication_slot_catalog_xmin;
3957 : :
3958 : 0 : LWLockRelease(ProcArrayLock);
3959 : 0 : }
3960 : :
3961 : : /*
3962 : : * XidCacheRemoveRunningXids
3963 : : *
3964 : : * Remove a bunch of TransactionIds from the list of known-running
3965 : : * subtransactions for my backend. Both the specified xid and those in
3966 : : * the xids[] array (of length nxids) are removed from the subxids cache.
3967 : : * latestXid must be the latest XID among the group.
3968 : : */
3969 : : void
3970 : 181 : XidCacheRemoveRunningXids(TransactionId xid,
3971 : : int nxids, const TransactionId *xids,
3972 : : TransactionId latestXid)
3973 : : {
3974 : 181 : int i,
3975 : : j;
3976 : 181 : XidCacheStatus *mysubxidstat;
3977 : :
3978 [ + - ]: 181 : Assert(TransactionIdIsValid(xid));
3979 : :
3980 : : /*
3981 : : * We must hold ProcArrayLock exclusively in order to remove transactions
3982 : : * from the PGPROC array. (See src/backend/access/transam/README.) It's
3983 : : * possible this could be relaxed since we know this routine is only used
3984 : : * to abort subtransactions, but pending closer analysis we'd best be
3985 : : * conservative.
3986 : : *
3987 : : * Note that we do not have to be careful about memory ordering of our own
3988 : : * reads wrt. GetNewTransactionId() here - only this process can modify
3989 : : * relevant fields of MyProc/ProcGlobal->xids[]. But we do have to be
3990 : : * careful about our own writes being well ordered.
3991 : : */
3992 : 181 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3993 : :
3994 : 181 : mysubxidstat = &ProcGlobal->subxidStates[MyProc->pgxactoff];
3995 : :
3996 : : /*
3997 : : * Under normal circumstances xid and xids[] will be in increasing order,
3998 : : * as will be the entries in subxids. Scan backwards to avoid O(N^2)
3999 : : * behavior when removing a lot of xids.
4000 : : */
4001 [ + + ]: 182 : for (i = nxids - 1; i >= 0; i--)
4002 : : {
4003 : 1 : TransactionId anxid = xids[i];
4004 : :
4005 [ - + ]: 1 : for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
4006 : : {
4007 [ + - ]: 1 : if (TransactionIdEquals(MyProc->subxids.xids[j], anxid))
4008 : : {
4009 : 1 : MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
4010 : 1 : pg_write_barrier();
4011 : 1 : mysubxidstat->count--;
4012 : 1 : MyProc->subxidStatus.count--;
4013 : 1 : break;
4014 : : }
4015 : 0 : }
4016 : :
4017 : : /*
4018 : : * Ordinarily we should have found it, unless the cache has
4019 : : * overflowed. However it's also possible for this routine to be
4020 : : * invoked multiple times for the same subtransaction, in case of an
4021 : : * error during AbortSubTransaction. So instead of Assert, emit a
4022 : : * debug warning.
4023 : : */
4024 [ - + # # ]: 1 : if (j < 0 && !MyProc->subxidStatus.overflowed)
4025 [ # # # # ]: 0 : elog(WARNING, "did not find subXID %u in MyProc", anxid);
4026 : 1 : }
4027 : :
4028 [ - + ]: 181 : for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
4029 : : {
4030 [ + - ]: 181 : if (TransactionIdEquals(MyProc->subxids.xids[j], xid))
4031 : : {
4032 : 181 : MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
4033 : 181 : pg_write_barrier();
4034 : 181 : mysubxidstat->count--;
4035 : 181 : MyProc->subxidStatus.count--;
4036 : 181 : break;
4037 : : }
4038 : 0 : }
4039 : : /* Ordinarily we should have found it, unless the cache has overflowed */
4040 [ - + # # ]: 181 : if (j < 0 && !MyProc->subxidStatus.overflowed)
4041 [ # # # # ]: 0 : elog(WARNING, "did not find subXID %u in MyProc", xid);
4042 : :
4043 : : /* Also advance global latestCompletedXid while holding the lock */
4044 : 181 : MaintainLatestCompletedXid(latestXid);
4045 : :
4046 : : /* ... and xactCompletionCount */
4047 : 181 : TransamVariables->xactCompletionCount++;
4048 : :
4049 : 181 : LWLockRelease(ProcArrayLock);
4050 : 181 : }
4051 : :
4052 : : #ifdef XIDCACHE_DEBUG
4053 : :
4054 : : /*
4055 : : * Print stats about effectiveness of XID cache
4056 : : */
4057 : : static void
4058 : : DisplayXidCache(void)
4059 : : {
4060 : : fprintf(stderr,
4061 : : "XidCache: xmin: %ld, known: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, knownassigned: %ld, nooflo: %ld, slow: %ld\n",
4062 : : xc_by_recent_xmin,
4063 : : xc_by_known_xact,
4064 : : xc_by_my_xact,
4065 : : xc_by_latest_xid,
4066 : : xc_by_main_xid,
4067 : : xc_by_child_xid,
4068 : : xc_by_known_assigned,
4069 : : xc_no_overflow,
4070 : : xc_slow_answer);
4071 : : }
4072 : : #endif /* XIDCACHE_DEBUG */
4073 : :
4074 : : /*
4075 : : * If rel != NULL, return test state appropriate for relation, otherwise
4076 : : * return state usable for all relations. The latter may consider XIDs as
4077 : : * not-yet-visible-to-everyone that a state for a specific relation would
4078 : : * already consider visible-to-everyone.
4079 : : *
4080 : : * This needs to be called while a snapshot is active or registered, otherwise
4081 : : * there are wraparound and other dangers.
4082 : : *
4083 : : * See comment for GlobalVisState for details.
4084 : : */
4085 : : GlobalVisState *
4086 : 4368463 : GlobalVisTestFor(Relation rel)
4087 : : {
4088 : 4368463 : GlobalVisState *state = NULL;
4089 : :
4090 : : /* XXX: we should assert that a snapshot is pushed or registered */
4091 [ + - ]: 4368463 : Assert(RecentXmin);
4092 : :
4093 [ - + + + : 4368463 : switch (GlobalVisHorizonKindForRel(rel))
+ ]
4094 : : {
4095 : : case VISHORIZON_SHARED:
4096 : 10629 : state = &GlobalVisSharedRels;
4097 : 10629 : break;
4098 : : case VISHORIZON_CATALOG:
4099 : 678293 : state = &GlobalVisCatalogRels;
4100 : 678293 : break;
4101 : : case VISHORIZON_DATA:
4102 : 3669103 : state = &GlobalVisDataRels;
4103 : 3669103 : break;
4104 : : case VISHORIZON_TEMP:
4105 : 10438 : state = &GlobalVisTempRels;
4106 : 10438 : break;
4107 : : }
4108 : :
4109 [ + - ]: 4368463 : Assert(FullTransactionIdIsValid(state->definitely_needed) &&
4110 : : FullTransactionIdIsValid(state->maybe_needed));
4111 : :
4112 : 8736926 : return state;
4113 : 4368463 : }
4114 : :
4115 : : /*
4116 : : * Return true if it's worth updating the accurate maybe_needed boundary.
4117 : : *
4118 : : * As it is somewhat expensive to determine xmin horizons, we don't want to
4119 : : * repeatedly do so when there is a low likelihood of it being beneficial.
4120 : : *
4121 : : * The current heuristic is that we update only if RecentXmin has changed
4122 : : * since the last update. If the oldest currently running transaction has not
4123 : : * finished, it is unlikely that recomputing the horizon would be useful.
4124 : : */
4125 : : static bool
4126 : 206924 : GlobalVisTestShouldUpdate(GlobalVisState *state)
4127 : : {
4128 : : /* hasn't been updated yet */
4129 [ + + ]: 206924 : if (!TransactionIdIsValid(ComputeXidHorizonsResultLastXmin))
4130 : 789 : return true;
4131 : :
4132 : : /*
4133 : : * If the maybe_needed/definitely_needed boundaries are the same, it's
4134 : : * unlikely to be beneficial to refresh boundaries.
4135 : : */
4136 [ - + ]: 206135 : if (FullTransactionIdFollowsOrEquals(state->maybe_needed,
4137 : : state->definitely_needed))
4138 : 0 : return false;
4139 : :
4140 : : /* does the last snapshot built have a different xmin? */
4141 : 206135 : return RecentXmin != ComputeXidHorizonsResultLastXmin;
4142 : 206924 : }
4143 : :
4144 : : static void
4145 : 0 : GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons)
4146 : : {
4147 : : GlobalVisSharedRels.maybe_needed =
4148 : 0 : FullXidRelativeTo(horizons->latest_completed,
4149 : 0 : horizons->shared_oldest_nonremovable);
4150 : : GlobalVisCatalogRels.maybe_needed =
4151 : 0 : FullXidRelativeTo(horizons->latest_completed,
4152 : 0 : horizons->catalog_oldest_nonremovable);
4153 : : GlobalVisDataRels.maybe_needed =
4154 : 0 : FullXidRelativeTo(horizons->latest_completed,
4155 : 0 : horizons->data_oldest_nonremovable);
4156 : : GlobalVisTempRels.maybe_needed =
4157 : 0 : FullXidRelativeTo(horizons->latest_completed,
4158 : 0 : horizons->temp_oldest_nonremovable);
4159 : :
4160 : : /*
4161 : : * In longer running transactions it's possible that transactions we
4162 : : * previously needed to treat as running aren't around anymore. So update
4163 : : * definitely_needed to not be earlier than maybe_needed.
4164 : : */
4165 : : GlobalVisSharedRels.definitely_needed =
4166 : 0 : FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
4167 : : GlobalVisSharedRels.definitely_needed);
4168 : : GlobalVisCatalogRels.definitely_needed =
4169 : 0 : FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
4170 : : GlobalVisCatalogRels.definitely_needed);
4171 : : GlobalVisDataRels.definitely_needed =
4172 : 0 : FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
4173 : : GlobalVisDataRels.definitely_needed);
4174 : 0 : GlobalVisTempRels.definitely_needed = GlobalVisTempRels.maybe_needed;
4175 : :
4176 : 0 : ComputeXidHorizonsResultLastXmin = RecentXmin;
4177 : 0 : }
4178 : :
4179 : : /*
4180 : : * Update boundaries in GlobalVis{Shared,Catalog, Data}Rels
4181 : : * using ComputeXidHorizons().
4182 : : */
4183 : : static void
4184 : 7917 : GlobalVisUpdate(void)
4185 : : {
4186 : 7917 : ComputeXidHorizonsResult horizons;
4187 : :
4188 : : /* updates the horizons as a side-effect */
4189 : 7917 : ComputeXidHorizons(&horizons);
4190 : 7917 : }
4191 : :
4192 : : /*
4193 : : * Return true if no snapshot still considers fxid to be running.
4194 : : *
4195 : : * The state passed needs to have been initialized for the relation fxid is
4196 : : * from (NULL is also OK), otherwise the result may not be correct.
4197 : : *
4198 : : * See comment for GlobalVisState for details.
4199 : : */
4200 : : bool
4201 : 2793757 : GlobalVisTestIsRemovableFullXid(GlobalVisState *state,
4202 : : FullTransactionId fxid)
4203 : : {
4204 : : /*
4205 : : * If fxid is older than maybe_needed bound, it definitely is visible to
4206 : : * everyone.
4207 : : */
4208 [ + + ]: 2793757 : if (FullTransactionIdPrecedes(fxid, state->maybe_needed))
4209 : 464127 : return true;
4210 : :
4211 : : /*
4212 : : * If fxid is >= definitely_needed bound, it is very likely to still be
4213 : : * considered running.
4214 : : */
4215 [ + + ]: 2329630 : if (FullTransactionIdFollowsOrEquals(fxid, state->definitely_needed))
4216 : 2122706 : return false;
4217 : :
4218 : : /*
4219 : : * fxid is between maybe_needed and definitely_needed, i.e. there might or
4220 : : * might not exist a snapshot considering fxid running. If it makes sense,
4221 : : * update boundaries and recheck.
4222 : : */
4223 [ + + ]: 206924 : if (GlobalVisTestShouldUpdate(state))
4224 : : {
4225 : 7917 : GlobalVisUpdate();
4226 : :
4227 [ + - ]: 7917 : Assert(FullTransactionIdPrecedes(fxid, state->definitely_needed));
4228 : :
4229 : 7917 : return FullTransactionIdPrecedes(fxid, state->maybe_needed);
4230 : : }
4231 : : else
4232 : 199007 : return false;
4233 : 2793757 : }
4234 : :
4235 : : /*
4236 : : * Wrapper around GlobalVisTestIsRemovableFullXid() for 32bit xids.
4237 : : *
4238 : : * It is crucial that this only gets called for xids from a source that
4239 : : * protects against xid wraparounds (e.g. from a table and thus protected by
4240 : : * relfrozenxid).
4241 : : */
4242 : : bool
4243 : 2793674 : GlobalVisTestIsRemovableXid(GlobalVisState *state, TransactionId xid)
4244 : : {
4245 : 2793674 : FullTransactionId fxid;
4246 : :
4247 : : /*
4248 : : * Convert 32 bit argument to FullTransactionId. We can do so safely
4249 : : * because we know the xid has to, at the very least, be between
4250 : : * [oldestXid, nextXid), i.e. within 2 billion of xid. To avoid taking a
4251 : : * lock to determine either, we can just compare with
4252 : : * state->definitely_needed, which was based on those value at the time
4253 : : * the current snapshot was built.
4254 : : */
4255 : 2793674 : fxid = FullXidRelativeTo(state->definitely_needed, xid);
4256 : :
4257 : 5587348 : return GlobalVisTestIsRemovableFullXid(state, fxid);
4258 : 2793674 : }
4259 : :
4260 : : /*
4261 : : * Convenience wrapper around GlobalVisTestFor() and
4262 : : * GlobalVisTestIsRemovableFullXid(), see their comments.
4263 : : */
4264 : : bool
4265 : 83 : GlobalVisCheckRemovableFullXid(Relation rel, FullTransactionId fxid)
4266 : : {
4267 : 83 : GlobalVisState *state;
4268 : :
4269 : 83 : state = GlobalVisTestFor(rel);
4270 : :
4271 : 166 : return GlobalVisTestIsRemovableFullXid(state, fxid);
4272 : 83 : }
4273 : :
4274 : : /*
4275 : : * Convenience wrapper around GlobalVisTestFor() and
4276 : : * GlobalVisTestIsRemovableXid(), see their comments.
4277 : : */
4278 : : bool
4279 : 2 : GlobalVisCheckRemovableXid(Relation rel, TransactionId xid)
4280 : : {
4281 : 2 : GlobalVisState *state;
4282 : :
4283 : 2 : state = GlobalVisTestFor(rel);
4284 : :
4285 : 4 : return GlobalVisTestIsRemovableXid(state, xid);
4286 : 2 : }
4287 : :
4288 : : /*
4289 : : * Convert a 32 bit transaction id into 64 bit transaction id, by assuming it
4290 : : * is within MaxTransactionId / 2 of XidFromFullTransactionId(rel).
4291 : : *
4292 : : * Be very careful about when to use this function. It can only safely be used
4293 : : * when there is a guarantee that xid is within MaxTransactionId / 2 xids of
4294 : : * rel. That e.g. can be guaranteed if the caller assures a snapshot is
4295 : : * held by the backend and xid is from a table (where vacuum/freezing ensures
4296 : : * the xid has to be within that range), or if xid is from the procarray and
4297 : : * prevents xid wraparound that way.
4298 : : */
4299 : : static inline FullTransactionId
4300 : 3137873 : FullXidRelativeTo(FullTransactionId rel, TransactionId xid)
4301 : : {
4302 : 3137873 : TransactionId rel_xid = XidFromFullTransactionId(rel);
4303 : :
4304 [ + - ]: 3137873 : Assert(TransactionIdIsValid(xid));
4305 [ + - ]: 3137873 : Assert(TransactionIdIsValid(rel_xid));
4306 : :
4307 : : /* not guaranteed to find issues, but likely to catch mistakes */
4308 : 3137873 : AssertTransactionIdInAllowableRange(xid);
4309 : :
4310 : 6275746 : return FullTransactionIdFromU64(U64FromFullTransactionId(rel)
4311 : 3137873 : + (int32) (xid - rel_xid));
4312 : 3137873 : }
4313 : :
4314 : :
4315 : : /* ----------------------------------------------
4316 : : * KnownAssignedTransactionIds sub-module
4317 : : * ----------------------------------------------
4318 : : */
4319 : :
4320 : : /*
4321 : : * In Hot Standby mode, we maintain a list of transactions that are (or were)
4322 : : * running on the primary at the current point in WAL. These XIDs must be
4323 : : * treated as running by standby transactions, even though they are not in
4324 : : * the standby server's PGPROC array.
4325 : : *
4326 : : * We record all XIDs that we know have been assigned. That includes all the
4327 : : * XIDs seen in WAL records, plus all unobserved XIDs that we can deduce have
4328 : : * been assigned. We can deduce the existence of unobserved XIDs because we
4329 : : * know XIDs are assigned in sequence, with no gaps. The KnownAssignedXids
4330 : : * list expands as new XIDs are observed or inferred, and contracts when
4331 : : * transaction completion records arrive.
4332 : : *
4333 : : * During hot standby we do not fret too much about the distinction between
4334 : : * top-level XIDs and subtransaction XIDs. We store both together in the
4335 : : * KnownAssignedXids list. In backends, this is copied into snapshots in
4336 : : * GetSnapshotData(), taking advantage of the fact that XidInMVCCSnapshot()
4337 : : * doesn't care about the distinction either. Subtransaction XIDs are
4338 : : * effectively treated as top-level XIDs and in the typical case pg_subtrans
4339 : : * links are *not* maintained (which does not affect visibility).
4340 : : *
4341 : : * We have room in KnownAssignedXids and in snapshots to hold maxProcs *
4342 : : * (1 + PGPROC_MAX_CACHED_SUBXIDS) XIDs, so every primary transaction must
4343 : : * report its subtransaction XIDs in a WAL XLOG_XACT_ASSIGNMENT record at
4344 : : * least every PGPROC_MAX_CACHED_SUBXIDS. When we receive one of these
4345 : : * records, we mark the subXIDs as children of the top XID in pg_subtrans,
4346 : : * and then remove them from KnownAssignedXids. This prevents overflow of
4347 : : * KnownAssignedXids and snapshots, at the cost that status checks for these
4348 : : * subXIDs will take a slower path through TransactionIdIsInProgress().
4349 : : * This means that KnownAssignedXids is not necessarily complete for subXIDs,
4350 : : * though it should be complete for top-level XIDs; this is the same situation
4351 : : * that holds with respect to the PGPROC entries in normal running.
4352 : : *
4353 : : * When we throw away subXIDs from KnownAssignedXids, we need to keep track of
4354 : : * that, similarly to tracking overflow of a PGPROC's subxids array. We do
4355 : : * that by remembering the lastOverflowedXid, ie the last thrown-away subXID.
4356 : : * As long as that is within the range of interesting XIDs, we have to assume
4357 : : * that subXIDs are missing from snapshots. (Note that subXID overflow occurs
4358 : : * on primary when 65th subXID arrives, whereas on standby it occurs when 64th
4359 : : * subXID arrives - that is not an error.)
4360 : : *
4361 : : * Should a backend on primary somehow disappear before it can write an abort
4362 : : * record, then we just leave those XIDs in KnownAssignedXids. They actually
4363 : : * aborted but we think they were running; the distinction is irrelevant
4364 : : * because either way any changes done by the transaction are not visible to
4365 : : * backends in the standby. We prune KnownAssignedXids when
4366 : : * XLOG_RUNNING_XACTS arrives, to forestall possible overflow of the
4367 : : * array due to such dead XIDs.
4368 : : */
4369 : :
4370 : : /*
4371 : : * RecordKnownAssignedTransactionIds
4372 : : * Record the given XID in KnownAssignedXids, as well as any preceding
4373 : : * unobserved XIDs.
4374 : : *
4375 : : * RecordKnownAssignedTransactionIds() should be run for *every* WAL record
4376 : : * associated with a transaction. Must be called for each record after we
4377 : : * have executed StartupCLOG() et al, since we must ExtendCLOG() etc..
4378 : : *
4379 : : * Called during recovery in analogy with and in place of GetNewTransactionId()
4380 : : */
4381 : : void
4382 : 0 : RecordKnownAssignedTransactionIds(TransactionId xid)
4383 : : {
4384 [ # # ]: 0 : Assert(standbyState >= STANDBY_INITIALIZED);
4385 [ # # ]: 0 : Assert(TransactionIdIsValid(xid));
4386 [ # # ]: 0 : Assert(TransactionIdIsValid(latestObservedXid));
4387 : :
4388 [ # # # # ]: 0 : elog(DEBUG4, "record known xact %u latestObservedXid %u",
4389 : : xid, latestObservedXid);
4390 : :
4391 : : /*
4392 : : * When a newly observed xid arrives, it is frequently the case that it is
4393 : : * *not* the next xid in sequence. When this occurs, we must treat the
4394 : : * intervening xids as running also.
4395 : : */
4396 [ # # ]: 0 : if (TransactionIdFollows(xid, latestObservedXid))
4397 : : {
4398 : 0 : TransactionId next_expected_xid;
4399 : :
4400 : : /*
4401 : : * Extend subtrans like we do in GetNewTransactionId() during normal
4402 : : * operation using individual extend steps. Note that we do not need
4403 : : * to extend clog since its extensions are WAL logged.
4404 : : *
4405 : : * This part has to be done regardless of standbyState since we
4406 : : * immediately start assigning subtransactions to their toplevel
4407 : : * transactions.
4408 : : */
4409 : 0 : next_expected_xid = latestObservedXid;
4410 [ # # ]: 0 : while (TransactionIdPrecedes(next_expected_xid, xid))
4411 : : {
4412 [ # # ]: 0 : TransactionIdAdvance(next_expected_xid);
4413 : 0 : ExtendSUBTRANS(next_expected_xid);
4414 : : }
4415 [ # # ]: 0 : Assert(next_expected_xid == xid);
4416 : :
4417 : : /*
4418 : : * If the KnownAssignedXids machinery isn't up yet, there's nothing
4419 : : * more to do since we don't track assigned xids yet.
4420 : : */
4421 [ # # ]: 0 : if (standbyState <= STANDBY_INITIALIZED)
4422 : : {
4423 : 0 : latestObservedXid = xid;
4424 : 0 : return;
4425 : : }
4426 : :
4427 : : /*
4428 : : * Add (latestObservedXid, xid] onto the KnownAssignedXids array.
4429 : : */
4430 : 0 : next_expected_xid = latestObservedXid;
4431 [ # # ]: 0 : TransactionIdAdvance(next_expected_xid);
4432 : 0 : KnownAssignedXidsAdd(next_expected_xid, xid, false);
4433 : :
4434 : : /*
4435 : : * Now we can advance latestObservedXid
4436 : : */
4437 : 0 : latestObservedXid = xid;
4438 : :
4439 : : /* TransamVariables->nextXid must be beyond any observed xid */
4440 : 0 : AdvanceNextFullTransactionIdPastXid(latestObservedXid);
4441 [ # # # ]: 0 : }
4442 : 0 : }
4443 : :
4444 : : /*
4445 : : * ExpireTreeKnownAssignedTransactionIds
4446 : : * Remove the given XIDs from KnownAssignedXids.
4447 : : *
4448 : : * Called during recovery in analogy with and in place of ProcArrayEndTransaction()
4449 : : */
4450 : : void
4451 : 0 : ExpireTreeKnownAssignedTransactionIds(TransactionId xid, int nsubxids,
4452 : : TransactionId *subxids, TransactionId max_xid)
4453 : : {
4454 [ # # ]: 0 : Assert(standbyState >= STANDBY_INITIALIZED);
4455 : :
4456 : : /*
4457 : : * Uses same locking as transaction commit
4458 : : */
4459 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4460 : :
4461 : 0 : KnownAssignedXidsRemoveTree(xid, nsubxids, subxids);
4462 : :
4463 : : /* As in ProcArrayEndTransaction, advance latestCompletedXid */
4464 : 0 : MaintainLatestCompletedXidRecovery(max_xid);
4465 : :
4466 : : /* ... and xactCompletionCount */
4467 : 0 : TransamVariables->xactCompletionCount++;
4468 : :
4469 : 0 : LWLockRelease(ProcArrayLock);
4470 : 0 : }
4471 : :
4472 : : /*
4473 : : * ExpireAllKnownAssignedTransactionIds
4474 : : * Remove all entries in KnownAssignedXids and reset lastOverflowedXid.
4475 : : */
4476 : : void
4477 : 0 : ExpireAllKnownAssignedTransactionIds(void)
4478 : : {
4479 : 0 : FullTransactionId latestXid;
4480 : :
4481 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4482 : 0 : KnownAssignedXidsRemovePreceding(InvalidTransactionId);
4483 : :
4484 : : /* Reset latestCompletedXid to nextXid - 1 */
4485 [ # # ]: 0 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
4486 : 0 : latestXid = TransamVariables->nextXid;
4487 : 0 : FullTransactionIdRetreat(&latestXid);
4488 : 0 : TransamVariables->latestCompletedXid = latestXid;
4489 : :
4490 : : /*
4491 : : * Any transactions that were in-progress were effectively aborted, so
4492 : : * advance xactCompletionCount.
4493 : : */
4494 : 0 : TransamVariables->xactCompletionCount++;
4495 : :
4496 : : /*
4497 : : * Reset lastOverflowedXid. Currently, lastOverflowedXid has no use after
4498 : : * the call of this function. But do this for unification with what
4499 : : * ExpireOldKnownAssignedTransactionIds() do.
4500 : : */
4501 : 0 : procArray->lastOverflowedXid = InvalidTransactionId;
4502 : 0 : LWLockRelease(ProcArrayLock);
4503 : 0 : }
4504 : :
4505 : : /*
4506 : : * ExpireOldKnownAssignedTransactionIds
4507 : : * Remove KnownAssignedXids entries preceding the given XID and
4508 : : * potentially reset lastOverflowedXid.
4509 : : */
4510 : : void
4511 : 0 : ExpireOldKnownAssignedTransactionIds(TransactionId xid)
4512 : : {
4513 : 0 : TransactionId latestXid;
4514 : :
4515 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4516 : :
4517 : : /* As in ProcArrayEndTransaction, advance latestCompletedXid */
4518 : 0 : latestXid = xid;
4519 [ # # ]: 0 : TransactionIdRetreat(latestXid);
4520 : 0 : MaintainLatestCompletedXidRecovery(latestXid);
4521 : :
4522 : : /* ... and xactCompletionCount */
4523 : 0 : TransamVariables->xactCompletionCount++;
4524 : :
4525 : : /*
4526 : : * Reset lastOverflowedXid if we know all transactions that have been
4527 : : * possibly running are being gone. Not doing so could cause an incorrect
4528 : : * lastOverflowedXid value, which makes extra snapshots be marked as
4529 : : * suboverflowed.
4530 : : */
4531 [ # # ]: 0 : if (TransactionIdPrecedes(procArray->lastOverflowedXid, xid))
4532 : 0 : procArray->lastOverflowedXid = InvalidTransactionId;
4533 : 0 : KnownAssignedXidsRemovePreceding(xid);
4534 : 0 : LWLockRelease(ProcArrayLock);
4535 : 0 : }
4536 : :
4537 : : /*
4538 : : * KnownAssignedTransactionIdsIdleMaintenance
4539 : : * Opportunistically do maintenance work when the startup process
4540 : : * is about to go idle.
4541 : : */
4542 : : void
4543 : 0 : KnownAssignedTransactionIdsIdleMaintenance(void)
4544 : : {
4545 : 0 : KnownAssignedXidsCompress(KAX_STARTUP_PROCESS_IDLE, false);
4546 : 0 : }
4547 : :
4548 : :
4549 : : /*
4550 : : * Private module functions to manipulate KnownAssignedXids
4551 : : *
4552 : : * There are 5 main uses of the KnownAssignedXids data structure:
4553 : : *
4554 : : * * backends taking snapshots - all valid XIDs need to be copied out
4555 : : * * backends seeking to determine presence of a specific XID
4556 : : * * startup process adding new known-assigned XIDs
4557 : : * * startup process removing specific XIDs as transactions end
4558 : : * * startup process pruning array when special WAL records arrive
4559 : : *
4560 : : * This data structure is known to be a hot spot during Hot Standby, so we
4561 : : * go to some lengths to make these operations as efficient and as concurrent
4562 : : * as possible.
4563 : : *
4564 : : * The XIDs are stored in an array in sorted order --- TransactionIdPrecedes
4565 : : * order, to be exact --- to allow binary search for specific XIDs. Note:
4566 : : * in general TransactionIdPrecedes would not provide a total order, but
4567 : : * we know that the entries present at any instant should not extend across
4568 : : * a large enough fraction of XID space to wrap around (the primary would
4569 : : * shut down for fear of XID wrap long before that happens). So it's OK to
4570 : : * use TransactionIdPrecedes as a binary-search comparator.
4571 : : *
4572 : : * It's cheap to maintain the sortedness during insertions, since new known
4573 : : * XIDs are always reported in XID order; we just append them at the right.
4574 : : *
4575 : : * To keep individual deletions cheap, we need to allow gaps in the array.
4576 : : * This is implemented by marking array elements as valid or invalid using
4577 : : * the parallel boolean array KnownAssignedXidsValid[]. A deletion is done
4578 : : * by setting KnownAssignedXidsValid[i] to false, *without* clearing the
4579 : : * XID entry itself. This preserves the property that the XID entries are
4580 : : * sorted, so we can do binary searches easily. Periodically we compress
4581 : : * out the unused entries; that's much cheaper than having to compress the
4582 : : * array immediately on every deletion.
4583 : : *
4584 : : * The actually valid items in KnownAssignedXids[] and KnownAssignedXidsValid[]
4585 : : * are those with indexes tail <= i < head; items outside this subscript range
4586 : : * have unspecified contents. When head reaches the end of the array, we
4587 : : * force compression of unused entries rather than wrapping around, since
4588 : : * allowing wraparound would greatly complicate the search logic. We maintain
4589 : : * an explicit tail pointer so that pruning of old XIDs can be done without
4590 : : * immediately moving the array contents. In most cases only a small fraction
4591 : : * of the array contains valid entries at any instant.
4592 : : *
4593 : : * Although only the startup process can ever change the KnownAssignedXids
4594 : : * data structure, we still need interlocking so that standby backends will
4595 : : * not observe invalid intermediate states. The convention is that backends
4596 : : * must hold shared ProcArrayLock to examine the array. To remove XIDs from
4597 : : * the array, the startup process must hold ProcArrayLock exclusively, for
4598 : : * the usual transactional reasons (compare commit/abort of a transaction
4599 : : * during normal running). Compressing unused entries out of the array
4600 : : * likewise requires exclusive lock. To add XIDs to the array, we just insert
4601 : : * them into slots to the right of the head pointer and then advance the head
4602 : : * pointer. This doesn't require any lock at all, but on machines with weak
4603 : : * memory ordering, we need to be careful that other processors see the array
4604 : : * element changes before they see the head pointer change. We handle this by
4605 : : * using memory barriers when reading or writing the head/tail pointers (unless
4606 : : * the caller holds ProcArrayLock exclusively).
4607 : : *
4608 : : * Algorithmic analysis:
4609 : : *
4610 : : * If we have a maximum of M slots, with N XIDs currently spread across
4611 : : * S elements then we have N <= S <= M always.
4612 : : *
4613 : : * * Adding a new XID is O(1) and needs no lock (unless compression must
4614 : : * happen)
4615 : : * * Compressing the array is O(S) and requires exclusive lock
4616 : : * * Removing an XID is O(logS) and requires exclusive lock
4617 : : * * Taking a snapshot is O(S) and requires shared lock
4618 : : * * Checking for an XID is O(logS) and requires shared lock
4619 : : *
4620 : : * In comparison, using a hash table for KnownAssignedXids would mean that
4621 : : * taking snapshots would be O(M). If we can maintain S << M then the
4622 : : * sorted array technique will deliver significantly faster snapshots.
4623 : : * If we try to keep S too small then we will spend too much time compressing,
4624 : : * so there is an optimal point for any workload mix. We use a heuristic to
4625 : : * decide when to compress the array, though trimming also helps reduce
4626 : : * frequency of compressing. The heuristic requires us to track the number of
4627 : : * currently valid XIDs in the array (N). Except in special cases, we'll
4628 : : * compress when S >= 2N. Bounding S at 2N in turn bounds the time for
4629 : : * taking a snapshot to be O(N), which it would have to be anyway.
4630 : : */
4631 : :
4632 : :
4633 : : /*
4634 : : * Compress KnownAssignedXids by shifting valid data down to the start of the
4635 : : * array, removing any gaps.
4636 : : *
4637 : : * A compression step is forced if "reason" is KAX_NO_SPACE, otherwise
4638 : : * we do it only if a heuristic indicates it's a good time to do it.
4639 : : *
4640 : : * Compression requires holding ProcArrayLock in exclusive mode.
4641 : : * Caller must pass haveLock = true if it already holds the lock.
4642 : : */
4643 : : static void
4644 : 0 : KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock)
4645 : : {
4646 : 0 : ProcArrayStruct *pArray = procArray;
4647 : 0 : int head,
4648 : : tail,
4649 : : nelements;
4650 : 0 : int compress_index;
4651 : 0 : int i;
4652 : :
4653 : : /* Counters for compression heuristics */
4654 : : static unsigned int transactionEndsCounter;
4655 : : static TimestampTz lastCompressTs;
4656 : :
4657 : : /* Tuning constants */
4658 : : #define KAX_COMPRESS_FREQUENCY 128 /* in transactions */
4659 : : #define KAX_COMPRESS_IDLE_INTERVAL 1000 /* in ms */
4660 : :
4661 : : /*
4662 : : * Since only the startup process modifies the head/tail pointers, we
4663 : : * don't need a lock to read them here.
4664 : : */
4665 : 0 : head = pArray->headKnownAssignedXids;
4666 : 0 : tail = pArray->tailKnownAssignedXids;
4667 : 0 : nelements = head - tail;
4668 : :
4669 : : /*
4670 : : * If we can choose whether to compress, use a heuristic to avoid
4671 : : * compressing too often or not often enough. "Compress" here simply
4672 : : * means moving the values to the beginning of the array, so it is not as
4673 : : * complex or costly as typical data compression algorithms.
4674 : : */
4675 [ # # ]: 0 : if (nelements == pArray->numKnownAssignedXids)
4676 : : {
4677 : : /*
4678 : : * When there are no gaps between head and tail, don't bother to
4679 : : * compress, except in the KAX_NO_SPACE case where we must compress to
4680 : : * create some space after the head.
4681 : : */
4682 [ # # ]: 0 : if (reason != KAX_NO_SPACE)
4683 : 0 : return;
4684 : 0 : }
4685 [ # # ]: 0 : else if (reason == KAX_TRANSACTION_END)
4686 : : {
4687 : : /*
4688 : : * Consider compressing only once every so many commits. Frequency
4689 : : * determined by benchmarks.
4690 : : */
4691 [ # # ]: 0 : if ((transactionEndsCounter++) % KAX_COMPRESS_FREQUENCY != 0)
4692 : 0 : return;
4693 : :
4694 : : /*
4695 : : * Furthermore, compress only if the used part of the array is less
4696 : : * than 50% full (see comments above).
4697 : : */
4698 [ # # ]: 0 : if (nelements < 2 * pArray->numKnownAssignedXids)
4699 : 0 : return;
4700 : 0 : }
4701 [ # # ]: 0 : else if (reason == KAX_STARTUP_PROCESS_IDLE)
4702 : : {
4703 : : /*
4704 : : * We're about to go idle for lack of new WAL, so we might as well
4705 : : * compress. But not too often, to avoid ProcArray lock contention
4706 : : * with readers.
4707 : : */
4708 [ # # ]: 0 : if (lastCompressTs != 0)
4709 : : {
4710 : 0 : TimestampTz compress_after;
4711 : :
4712 : 0 : compress_after = TimestampTzPlusMilliseconds(lastCompressTs,
4713 : : KAX_COMPRESS_IDLE_INTERVAL);
4714 [ # # ]: 0 : if (GetCurrentTimestamp() < compress_after)
4715 : 0 : return;
4716 [ # # ]: 0 : }
4717 : 0 : }
4718 : :
4719 : : /* Need to compress, so get the lock if we don't have it. */
4720 [ # # ]: 0 : if (!haveLock)
4721 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4722 : :
4723 : : /*
4724 : : * We compress the array by reading the valid values from tail to head,
4725 : : * re-aligning data to 0th element.
4726 : : */
4727 : 0 : compress_index = 0;
4728 [ # # ]: 0 : for (i = tail; i < head; i++)
4729 : : {
4730 [ # # ]: 0 : if (KnownAssignedXidsValid[i])
4731 : : {
4732 : 0 : KnownAssignedXids[compress_index] = KnownAssignedXids[i];
4733 : 0 : KnownAssignedXidsValid[compress_index] = true;
4734 : 0 : compress_index++;
4735 : 0 : }
4736 : 0 : }
4737 [ # # ]: 0 : Assert(compress_index == pArray->numKnownAssignedXids);
4738 : :
4739 : 0 : pArray->tailKnownAssignedXids = 0;
4740 : 0 : pArray->headKnownAssignedXids = compress_index;
4741 : :
4742 [ # # ]: 0 : if (!haveLock)
4743 : 0 : LWLockRelease(ProcArrayLock);
4744 : :
4745 : : /* Update timestamp for maintenance. No need to hold lock for this. */
4746 : 0 : lastCompressTs = GetCurrentTimestamp();
4747 [ # # ]: 0 : }
4748 : :
4749 : : /*
4750 : : * Add xids into KnownAssignedXids at the head of the array.
4751 : : *
4752 : : * xids from from_xid to to_xid, inclusive, are added to the array.
4753 : : *
4754 : : * If exclusive_lock is true then caller already holds ProcArrayLock in
4755 : : * exclusive mode, so we need no extra locking here. Else caller holds no
4756 : : * lock, so we need to be sure we maintain sufficient interlocks against
4757 : : * concurrent readers. (Only the startup process ever calls this, so no need
4758 : : * to worry about concurrent writers.)
4759 : : */
4760 : : static void
4761 : 0 : KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
4762 : : bool exclusive_lock)
4763 : : {
4764 : 0 : ProcArrayStruct *pArray = procArray;
4765 : 0 : TransactionId next_xid;
4766 : 0 : int head,
4767 : : tail;
4768 : 0 : int nxids;
4769 : 0 : int i;
4770 : :
4771 [ # # ]: 0 : Assert(TransactionIdPrecedesOrEquals(from_xid, to_xid));
4772 : :
4773 : : /*
4774 : : * Calculate how many array slots we'll need. Normally this is cheap; in
4775 : : * the unusual case where the XIDs cross the wrap point, we do it the hard
4776 : : * way.
4777 : : */
4778 [ # # ]: 0 : if (to_xid >= from_xid)
4779 : 0 : nxids = to_xid - from_xid + 1;
4780 : : else
4781 : : {
4782 : 0 : nxids = 1;
4783 : 0 : next_xid = from_xid;
4784 [ # # ]: 0 : while (TransactionIdPrecedes(next_xid, to_xid))
4785 : : {
4786 : 0 : nxids++;
4787 [ # # ]: 0 : TransactionIdAdvance(next_xid);
4788 : : }
4789 : : }
4790 : :
4791 : : /*
4792 : : * Since only the startup process modifies the head/tail pointers, we
4793 : : * don't need a lock to read them here.
4794 : : */
4795 : 0 : head = pArray->headKnownAssignedXids;
4796 : 0 : tail = pArray->tailKnownAssignedXids;
4797 : :
4798 [ # # ]: 0 : Assert(head >= 0 && head <= pArray->maxKnownAssignedXids);
4799 [ # # ]: 0 : Assert(tail >= 0 && tail < pArray->maxKnownAssignedXids);
4800 : :
4801 : : /*
4802 : : * Verify that insertions occur in TransactionId sequence. Note that even
4803 : : * if the last existing element is marked invalid, it must still have a
4804 : : * correctly sequenced XID value.
4805 : : */
4806 [ # # # # ]: 0 : if (head > tail &&
4807 : 0 : TransactionIdFollowsOrEquals(KnownAssignedXids[head - 1], from_xid))
4808 : : {
4809 : 0 : KnownAssignedXidsDisplay(LOG);
4810 [ # # # # ]: 0 : elog(ERROR, "out-of-order XID insertion in KnownAssignedXids");
4811 : 0 : }
4812 : :
4813 : : /*
4814 : : * If our xids won't fit in the remaining space, compress out free space
4815 : : */
4816 [ # # ]: 0 : if (head + nxids > pArray->maxKnownAssignedXids)
4817 : : {
4818 : 0 : KnownAssignedXidsCompress(KAX_NO_SPACE, exclusive_lock);
4819 : :
4820 : 0 : head = pArray->headKnownAssignedXids;
4821 : : /* note: we no longer care about the tail pointer */
4822 : :
4823 : : /*
4824 : : * If it still won't fit then we're out of memory
4825 : : */
4826 [ # # ]: 0 : if (head + nxids > pArray->maxKnownAssignedXids)
4827 [ # # # # ]: 0 : elog(ERROR, "too many KnownAssignedXids");
4828 : 0 : }
4829 : :
4830 : : /* Now we can insert the xids into the space starting at head */
4831 : 0 : next_xid = from_xid;
4832 [ # # ]: 0 : for (i = 0; i < nxids; i++)
4833 : : {
4834 : 0 : KnownAssignedXids[head] = next_xid;
4835 : 0 : KnownAssignedXidsValid[head] = true;
4836 [ # # ]: 0 : TransactionIdAdvance(next_xid);
4837 : 0 : head++;
4838 : 0 : }
4839 : :
4840 : : /* Adjust count of number of valid entries */
4841 : 0 : pArray->numKnownAssignedXids += nxids;
4842 : :
4843 : : /*
4844 : : * Now update the head pointer. We use a write barrier to ensure that
4845 : : * other processors see the above array updates before they see the head
4846 : : * pointer change. The barrier isn't required if we're holding
4847 : : * ProcArrayLock exclusively.
4848 : : */
4849 [ # # ]: 0 : if (!exclusive_lock)
4850 : 0 : pg_write_barrier();
4851 : :
4852 : 0 : pArray->headKnownAssignedXids = head;
4853 : 0 : }
4854 : :
4855 : : /*
4856 : : * KnownAssignedXidsSearch
4857 : : *
4858 : : * Searches KnownAssignedXids for a specific xid and optionally removes it.
4859 : : * Returns true if it was found, false if not.
4860 : : *
4861 : : * Caller must hold ProcArrayLock in shared or exclusive mode.
4862 : : * Exclusive lock must be held for remove = true.
4863 : : */
4864 : : static bool
4865 : 0 : KnownAssignedXidsSearch(TransactionId xid, bool remove)
4866 : : {
4867 : 0 : ProcArrayStruct *pArray = procArray;
4868 : 0 : int first,
4869 : : last;
4870 : 0 : int head;
4871 : 0 : int tail;
4872 : 0 : int result_index = -1;
4873 : :
4874 : 0 : tail = pArray->tailKnownAssignedXids;
4875 : 0 : head = pArray->headKnownAssignedXids;
4876 : :
4877 : : /*
4878 : : * Only the startup process removes entries, so we don't need the read
4879 : : * barrier in that case.
4880 : : */
4881 [ # # ]: 0 : if (!remove)
4882 : 0 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
4883 : :
4884 : : /*
4885 : : * Standard binary search. Note we can ignore the KnownAssignedXidsValid
4886 : : * array here, since even invalid entries will contain sorted XIDs.
4887 : : */
4888 : 0 : first = tail;
4889 : 0 : last = head - 1;
4890 [ # # ]: 0 : while (first <= last)
4891 : : {
4892 : 0 : int mid_index;
4893 : 0 : TransactionId mid_xid;
4894 : :
4895 : 0 : mid_index = (first + last) / 2;
4896 : 0 : mid_xid = KnownAssignedXids[mid_index];
4897 : :
4898 [ # # ]: 0 : if (xid == mid_xid)
4899 : : {
4900 : 0 : result_index = mid_index;
4901 : 0 : break;
4902 : : }
4903 [ # # ]: 0 : else if (TransactionIdPrecedes(xid, mid_xid))
4904 : 0 : last = mid_index - 1;
4905 : : else
4906 : 0 : first = mid_index + 1;
4907 [ # # # ]: 0 : }
4908 : :
4909 [ # # ]: 0 : if (result_index < 0)
4910 : 0 : return false; /* not in array */
4911 : :
4912 [ # # ]: 0 : if (!KnownAssignedXidsValid[result_index])
4913 : 0 : return false; /* in array, but invalid */
4914 : :
4915 [ # # ]: 0 : if (remove)
4916 : : {
4917 : 0 : KnownAssignedXidsValid[result_index] = false;
4918 : :
4919 : 0 : pArray->numKnownAssignedXids--;
4920 [ # # ]: 0 : Assert(pArray->numKnownAssignedXids >= 0);
4921 : :
4922 : : /*
4923 : : * If we're removing the tail element then advance tail pointer over
4924 : : * any invalid elements. This will speed future searches.
4925 : : */
4926 [ # # ]: 0 : if (result_index == tail)
4927 : : {
4928 : 0 : tail++;
4929 [ # # # # ]: 0 : while (tail < head && !KnownAssignedXidsValid[tail])
4930 : 0 : tail++;
4931 [ # # ]: 0 : if (tail >= head)
4932 : : {
4933 : : /* Array is empty, so we can reset both pointers */
4934 : 0 : pArray->headKnownAssignedXids = 0;
4935 : 0 : pArray->tailKnownAssignedXids = 0;
4936 : 0 : }
4937 : : else
4938 : : {
4939 : 0 : pArray->tailKnownAssignedXids = tail;
4940 : : }
4941 : 0 : }
4942 : 0 : }
4943 : :
4944 : 0 : return true;
4945 : 0 : }
4946 : :
4947 : : /*
4948 : : * Is the specified XID present in KnownAssignedXids[]?
4949 : : *
4950 : : * Caller must hold ProcArrayLock in shared or exclusive mode.
4951 : : */
4952 : : static bool
4953 : 0 : KnownAssignedXidExists(TransactionId xid)
4954 : : {
4955 [ # # ]: 0 : Assert(TransactionIdIsValid(xid));
4956 : :
4957 : 0 : return KnownAssignedXidsSearch(xid, false);
4958 : : }
4959 : :
4960 : : /*
4961 : : * Remove the specified XID from KnownAssignedXids[].
4962 : : *
4963 : : * Caller must hold ProcArrayLock in exclusive mode.
4964 : : */
4965 : : static void
4966 : 0 : KnownAssignedXidsRemove(TransactionId xid)
4967 : : {
4968 [ # # ]: 0 : Assert(TransactionIdIsValid(xid));
4969 : :
4970 [ # # # # ]: 0 : elog(DEBUG4, "remove KnownAssignedXid %u", xid);
4971 : :
4972 : : /*
4973 : : * Note: we cannot consider it an error to remove an XID that's not
4974 : : * present. We intentionally remove subxact IDs while processing
4975 : : * XLOG_XACT_ASSIGNMENT, to avoid array overflow. Then those XIDs will be
4976 : : * removed again when the top-level xact commits or aborts.
4977 : : *
4978 : : * It might be possible to track such XIDs to distinguish this case from
4979 : : * actual errors, but it would be complicated and probably not worth it.
4980 : : * So, just ignore the search result.
4981 : : */
4982 : 0 : (void) KnownAssignedXidsSearch(xid, true);
4983 : 0 : }
4984 : :
4985 : : /*
4986 : : * KnownAssignedXidsRemoveTree
4987 : : * Remove xid (if it's not InvalidTransactionId) and all the subxids.
4988 : : *
4989 : : * Caller must hold ProcArrayLock in exclusive mode.
4990 : : */
4991 : : static void
4992 : 0 : KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
4993 : : TransactionId *subxids)
4994 : : {
4995 : 0 : int i;
4996 : :
4997 [ # # ]: 0 : if (TransactionIdIsValid(xid))
4998 : 0 : KnownAssignedXidsRemove(xid);
4999 : :
5000 [ # # ]: 0 : for (i = 0; i < nsubxids; i++)
5001 : 0 : KnownAssignedXidsRemove(subxids[i]);
5002 : :
5003 : : /* Opportunistically compress the array */
5004 : 0 : KnownAssignedXidsCompress(KAX_TRANSACTION_END, true);
5005 : 0 : }
5006 : :
5007 : : /*
5008 : : * Prune KnownAssignedXids up to, but *not* including xid. If xid is invalid
5009 : : * then clear the whole table.
5010 : : *
5011 : : * Caller must hold ProcArrayLock in exclusive mode.
5012 : : */
5013 : : static void
5014 : 0 : KnownAssignedXidsRemovePreceding(TransactionId removeXid)
5015 : : {
5016 : 0 : ProcArrayStruct *pArray = procArray;
5017 : 0 : int count = 0;
5018 : 0 : int head,
5019 : : tail,
5020 : : i;
5021 : :
5022 [ # # ]: 0 : if (!TransactionIdIsValid(removeXid))
5023 : : {
5024 [ # # # # ]: 0 : elog(DEBUG4, "removing all KnownAssignedXids");
5025 : 0 : pArray->numKnownAssignedXids = 0;
5026 : 0 : pArray->headKnownAssignedXids = pArray->tailKnownAssignedXids = 0;
5027 : 0 : return;
5028 : : }
5029 : :
5030 [ # # # # ]: 0 : elog(DEBUG4, "prune KnownAssignedXids to %u", removeXid);
5031 : :
5032 : : /*
5033 : : * Mark entries invalid starting at the tail. Since array is sorted, we
5034 : : * can stop as soon as we reach an entry >= removeXid.
5035 : : */
5036 : 0 : tail = pArray->tailKnownAssignedXids;
5037 : 0 : head = pArray->headKnownAssignedXids;
5038 : :
5039 [ # # ]: 0 : for (i = tail; i < head; i++)
5040 : : {
5041 [ # # ]: 0 : if (KnownAssignedXidsValid[i])
5042 : : {
5043 : 0 : TransactionId knownXid = KnownAssignedXids[i];
5044 : :
5045 [ # # ]: 0 : if (TransactionIdFollowsOrEquals(knownXid, removeXid))
5046 : 0 : break;
5047 : :
5048 [ # # ]: 0 : if (!StandbyTransactionIdIsPrepared(knownXid))
5049 : : {
5050 : 0 : KnownAssignedXidsValid[i] = false;
5051 : 0 : count++;
5052 : 0 : }
5053 [ # # ]: 0 : }
5054 : 0 : }
5055 : :
5056 : 0 : pArray->numKnownAssignedXids -= count;
5057 [ # # ]: 0 : Assert(pArray->numKnownAssignedXids >= 0);
5058 : :
5059 : : /*
5060 : : * Advance the tail pointer if we've marked the tail item invalid.
5061 : : */
5062 [ # # ]: 0 : for (i = tail; i < head; i++)
5063 : : {
5064 [ # # ]: 0 : if (KnownAssignedXidsValid[i])
5065 : 0 : break;
5066 : 0 : }
5067 [ # # ]: 0 : if (i >= head)
5068 : : {
5069 : : /* Array is empty, so we can reset both pointers */
5070 : 0 : pArray->headKnownAssignedXids = 0;
5071 : 0 : pArray->tailKnownAssignedXids = 0;
5072 : 0 : }
5073 : : else
5074 : : {
5075 : 0 : pArray->tailKnownAssignedXids = i;
5076 : : }
5077 : :
5078 : : /* Opportunistically compress the array */
5079 : 0 : KnownAssignedXidsCompress(KAX_PRUNE, true);
5080 : 0 : }
5081 : :
5082 : : /*
5083 : : * KnownAssignedXidsGet - Get an array of xids by scanning KnownAssignedXids.
5084 : : * We filter out anything >= xmax.
5085 : : *
5086 : : * Returns the number of XIDs stored into xarray[]. Caller is responsible
5087 : : * that array is large enough.
5088 : : *
5089 : : * Caller must hold ProcArrayLock in (at least) shared mode.
5090 : : */
5091 : : static int
5092 : 0 : KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax)
5093 : : {
5094 : 0 : TransactionId xtmp = InvalidTransactionId;
5095 : :
5096 : 0 : return KnownAssignedXidsGetAndSetXmin(xarray, &xtmp, xmax);
5097 : 0 : }
5098 : :
5099 : : /*
5100 : : * KnownAssignedXidsGetAndSetXmin - as KnownAssignedXidsGet, plus
5101 : : * we reduce *xmin to the lowest xid value seen if not already lower.
5102 : : *
5103 : : * Caller must hold ProcArrayLock in (at least) shared mode.
5104 : : */
5105 : : static int
5106 : 0 : KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
5107 : : TransactionId xmax)
5108 : : {
5109 : 0 : int count = 0;
5110 : 0 : int head,
5111 : : tail;
5112 : 0 : int i;
5113 : :
5114 : : /*
5115 : : * Fetch head just once, since it may change while we loop. We can stop
5116 : : * once we reach the initially seen head, since we are certain that an xid
5117 : : * cannot enter and then leave the array while we hold ProcArrayLock. We
5118 : : * might miss newly-added xids, but they should be >= xmax so irrelevant
5119 : : * anyway.
5120 : : */
5121 : 0 : tail = procArray->tailKnownAssignedXids;
5122 : 0 : head = procArray->headKnownAssignedXids;
5123 : :
5124 : 0 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
5125 : :
5126 [ # # ]: 0 : for (i = tail; i < head; i++)
5127 : : {
5128 : : /* Skip any gaps in the array */
5129 [ # # ]: 0 : if (KnownAssignedXidsValid[i])
5130 : : {
5131 : 0 : TransactionId knownXid = KnownAssignedXids[i];
5132 : :
5133 : : /*
5134 : : * Update xmin if required. Only the first XID need be checked,
5135 : : * since the array is sorted.
5136 : : */
5137 [ # # # # ]: 0 : if (count == 0 &&
5138 : 0 : TransactionIdPrecedes(knownXid, *xmin))
5139 : 0 : *xmin = knownXid;
5140 : :
5141 : : /*
5142 : : * Filter out anything >= xmax, again relying on sorted property
5143 : : * of array.
5144 : : */
5145 [ # # # # ]: 0 : if (TransactionIdIsValid(xmax) &&
5146 : 0 : TransactionIdFollowsOrEquals(knownXid, xmax))
5147 : 0 : break;
5148 : :
5149 : : /* Add knownXid into output array */
5150 : 0 : xarray[count++] = knownXid;
5151 [ # # # ]: 0 : }
5152 : 0 : }
5153 : :
5154 : 0 : return count;
5155 : 0 : }
5156 : :
5157 : : /*
5158 : : * Get oldest XID in the KnownAssignedXids array, or InvalidTransactionId
5159 : : * if nothing there.
5160 : : */
5161 : : static TransactionId
5162 : 0 : KnownAssignedXidsGetOldestXmin(void)
5163 : : {
5164 : 0 : int head,
5165 : : tail;
5166 : 0 : int i;
5167 : :
5168 : : /*
5169 : : * Fetch head just once, since it may change while we loop.
5170 : : */
5171 : 0 : tail = procArray->tailKnownAssignedXids;
5172 : 0 : head = procArray->headKnownAssignedXids;
5173 : :
5174 : 0 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
5175 : :
5176 [ # # ]: 0 : for (i = tail; i < head; i++)
5177 : : {
5178 : : /* Skip any gaps in the array */
5179 [ # # ]: 0 : if (KnownAssignedXidsValid[i])
5180 : 0 : return KnownAssignedXids[i];
5181 : 0 : }
5182 : :
5183 : 0 : return InvalidTransactionId;
5184 : 0 : }
5185 : :
5186 : : /*
5187 : : * Display KnownAssignedXids to provide debug trail
5188 : : *
5189 : : * Currently this is only called within startup process, so we need no
5190 : : * special locking.
5191 : : *
5192 : : * Note this is pretty expensive, and much of the expense will be incurred
5193 : : * even if the elog message will get discarded. It's not currently called
5194 : : * in any performance-critical places, however, so no need to be tenser.
5195 : : */
5196 : : static void
5197 : 0 : KnownAssignedXidsDisplay(int trace_level)
5198 : : {
5199 : 0 : ProcArrayStruct *pArray = procArray;
5200 : 0 : StringInfoData buf;
5201 : 0 : int head,
5202 : : tail,
5203 : : i;
5204 : 0 : int nxids = 0;
5205 : :
5206 : 0 : tail = pArray->tailKnownAssignedXids;
5207 : 0 : head = pArray->headKnownAssignedXids;
5208 : :
5209 : 0 : initStringInfo(&buf);
5210 : :
5211 [ # # ]: 0 : for (i = tail; i < head; i++)
5212 : : {
5213 [ # # ]: 0 : if (KnownAssignedXidsValid[i])
5214 : : {
5215 : 0 : nxids++;
5216 : 0 : appendStringInfo(&buf, "[%d]=%u ", i, KnownAssignedXids[i]);
5217 : 0 : }
5218 : 0 : }
5219 : :
5220 [ # # # # : 0 : elog(trace_level, "%d KnownAssignedXids (num=%d tail=%d head=%d) %s",
# # # # #
# ]
5221 : : nxids,
5222 : : pArray->numKnownAssignedXids,
5223 : : pArray->tailKnownAssignedXids,
5224 : : pArray->headKnownAssignedXids,
5225 : : buf.data);
5226 : :
5227 : 0 : pfree(buf.data);
5228 : 0 : }
5229 : :
5230 : : /*
5231 : : * KnownAssignedXidsReset
5232 : : * Resets KnownAssignedXids to be empty
5233 : : */
5234 : : static void
5235 : 0 : KnownAssignedXidsReset(void)
5236 : : {
5237 : 0 : ProcArrayStruct *pArray = procArray;
5238 : :
5239 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
5240 : :
5241 : 0 : pArray->numKnownAssignedXids = 0;
5242 : 0 : pArray->tailKnownAssignedXids = 0;
5243 : 0 : pArray->headKnownAssignedXids = 0;
5244 : :
5245 : 0 : LWLockRelease(ProcArrayLock);
5246 : 0 : }
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