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1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * sync.c
4 : : * File synchronization management code.
5 : : *
6 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
7 : : * Portions Copyright (c) 1994, Regents of the University of California
8 : : *
9 : : *
10 : : * IDENTIFICATION
11 : : * src/backend/storage/sync/sync.c
12 : : *
13 : : *-------------------------------------------------------------------------
14 : : */
15 : : #include "postgres.h"
16 : :
17 : : #include <unistd.h>
18 : : #include <fcntl.h>
19 : : #include <sys/file.h>
20 : :
21 : : #include "access/clog.h"
22 : : #include "access/commit_ts.h"
23 : : #include "access/multixact.h"
24 : : #include "access/xlog.h"
25 : : #include "miscadmin.h"
26 : : #include "pgstat.h"
27 : : #include "portability/instr_time.h"
28 : : #include "postmaster/bgwriter.h"
29 : : #include "storage/fd.h"
30 : : #include "storage/latch.h"
31 : : #include "storage/md.h"
32 : : #include "utils/hsearch.h"
33 : : #include "utils/memutils.h"
34 : :
35 : : /*
36 : : * In some contexts (currently, standalone backends and the checkpointer)
37 : : * we keep track of pending fsync operations: we need to remember all relation
38 : : * segments that have been written since the last checkpoint, so that we can
39 : : * fsync them down to disk before completing the next checkpoint. This hash
40 : : * table remembers the pending operations. We use a hash table mostly as
41 : : * a convenient way of merging duplicate requests.
42 : : *
43 : : * We use a similar mechanism to remember no-longer-needed files that can
44 : : * be deleted after the next checkpoint, but we use a linked list instead of
45 : : * a hash table, because we don't expect there to be any duplicate requests.
46 : : *
47 : : * These mechanisms are only used for non-temp relations; we never fsync
48 : : * temp rels, nor do we need to postpone their deletion (see comments in
49 : : * mdunlink).
50 : : *
51 : : * (Regular backends do not track pending operations locally, but forward
52 : : * them to the checkpointer.)
53 : : */
54 : : typedef uint16 CycleCtr; /* can be any convenient integer size */
55 : :
56 : : typedef struct
57 : : {
58 : : FileTag tag; /* identifies handler and file */
59 : : CycleCtr cycle_ctr; /* sync_cycle_ctr of oldest request */
60 : : bool canceled; /* canceled is true if we canceled "recently" */
61 : : } PendingFsyncEntry;
62 : :
63 : : typedef struct
64 : : {
65 : : FileTag tag; /* identifies handler and file */
66 : : CycleCtr cycle_ctr; /* checkpoint_cycle_ctr when request was made */
67 : : bool canceled; /* true if request has been canceled */
68 : : } PendingUnlinkEntry;
69 : :
70 : : static HTAB *pendingOps = NULL;
71 : : static List *pendingUnlinks = NIL;
72 : : static MemoryContext pendingOpsCxt; /* context for the above */
73 : :
74 : : static CycleCtr sync_cycle_ctr = 0;
75 : : static CycleCtr checkpoint_cycle_ctr = 0;
76 : :
77 : : /* Intervals for calling AbsorbSyncRequests */
78 : : #define FSYNCS_PER_ABSORB 10
79 : : #define UNLINKS_PER_ABSORB 10
80 : :
81 : : /*
82 : : * Function pointers for handling sync and unlink requests.
83 : : */
84 : : typedef struct SyncOps
85 : : {
86 : : int (*sync_syncfiletag) (const FileTag *ftag, char *path);
87 : : int (*sync_unlinkfiletag) (const FileTag *ftag, char *path);
88 : : bool (*sync_filetagmatches) (const FileTag *ftag,
89 : : const FileTag *candidate);
90 : : } SyncOps;
91 : :
92 : : /*
93 : : * These indexes must correspond to the values of the SyncRequestHandler enum.
94 : : */
95 : : static const SyncOps syncsw[] = {
96 : : /* magnetic disk */
97 : : [SYNC_HANDLER_MD] = {
98 : : .sync_syncfiletag = mdsyncfiletag,
99 : : .sync_unlinkfiletag = mdunlinkfiletag,
100 : : .sync_filetagmatches = mdfiletagmatches
101 : : },
102 : : /* pg_xact */
103 : : [SYNC_HANDLER_CLOG] = {
104 : : .sync_syncfiletag = clogsyncfiletag
105 : : },
106 : : /* pg_commit_ts */
107 : : [SYNC_HANDLER_COMMIT_TS] = {
108 : : .sync_syncfiletag = committssyncfiletag
109 : : },
110 : : /* pg_multixact/offsets */
111 : : [SYNC_HANDLER_MULTIXACT_OFFSET] = {
112 : : .sync_syncfiletag = multixactoffsetssyncfiletag
113 : : },
114 : : /* pg_multixact/members */
115 : : [SYNC_HANDLER_MULTIXACT_MEMBER] = {
116 : : .sync_syncfiletag = multixactmemberssyncfiletag
117 : : }
118 : : };
119 : :
120 : : /*
121 : : * Initialize data structures for the file sync tracking.
122 : : */
123 : : void
124 : 806 : InitSync(void)
125 : : {
126 : : /*
127 : : * Create pending-operations hashtable if we need it. Currently, we need
128 : : * it if we are standalone (not under a postmaster) or if we are a
129 : : * checkpointer auxiliary process.
130 : : */
131 [ + + + + ]: 806 : if (!IsUnderPostmaster || AmCheckpointerProcess())
132 : : {
133 : 3 : HASHCTL hash_ctl;
134 : :
135 : : /*
136 : : * XXX: The checkpointer needs to add entries to the pending ops table
137 : : * when absorbing fsync requests. That is done within a critical
138 : : * section, which isn't usually allowed, but we make an exception. It
139 : : * means that there's a theoretical possibility that you run out of
140 : : * memory while absorbing fsync requests, which leads to a PANIC.
141 : : * Fortunately the hash table is small so that's unlikely to happen in
142 : : * practice.
143 : : */
144 : 3 : pendingOpsCxt = AllocSetContextCreate(TopMemoryContext,
145 : : "Pending ops context",
146 : : ALLOCSET_DEFAULT_SIZES);
147 : 3 : MemoryContextAllowInCriticalSection(pendingOpsCxt, true);
148 : :
149 : 3 : hash_ctl.keysize = sizeof(FileTag);
150 : 3 : hash_ctl.entrysize = sizeof(PendingFsyncEntry);
151 : 3 : hash_ctl.hcxt = pendingOpsCxt;
152 : 3 : pendingOps = hash_create("Pending Ops Table",
153 : : 100L,
154 : : &hash_ctl,
155 : : HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
156 : 3 : pendingUnlinks = NIL;
157 : 3 : }
158 : 806 : }
159 : :
160 : : /*
161 : : * SyncPreCheckpoint() -- Do pre-checkpoint work
162 : : *
163 : : * To distinguish unlink requests that arrived before this checkpoint
164 : : * started from those that arrived during the checkpoint, we use a cycle
165 : : * counter similar to the one we use for fsync requests. That cycle
166 : : * counter is incremented here.
167 : : *
168 : : * This must be called *before* the checkpoint REDO point is determined.
169 : : * That ensures that we won't delete files too soon. Since this calls
170 : : * AbsorbSyncRequests(), which performs memory allocations, it cannot be
171 : : * called within a critical section.
172 : : *
173 : : * Note that we can't do anything here that depends on the assumption
174 : : * that the checkpoint will be completed.
175 : : */
176 : : void
177 : 7 : SyncPreCheckpoint(void)
178 : : {
179 : : /*
180 : : * Operations such as DROP TABLESPACE assume that the next checkpoint will
181 : : * process all recently forwarded unlink requests, but if they aren't
182 : : * absorbed prior to advancing the cycle counter, they won't be processed
183 : : * until a future checkpoint. The following absorb ensures that any
184 : : * unlink requests forwarded before the checkpoint began will be processed
185 : : * in the current checkpoint.
186 : : */
187 : 7 : AbsorbSyncRequests();
188 : :
189 : : /*
190 : : * Any unlink requests arriving after this point will be assigned the next
191 : : * cycle counter, and won't be unlinked until next checkpoint.
192 : : */
193 : 7 : checkpoint_cycle_ctr++;
194 : 7 : }
195 : :
196 : : /*
197 : : * SyncPostCheckpoint() -- Do post-checkpoint work
198 : : *
199 : : * Remove any lingering files that can now be safely removed.
200 : : */
201 : : void
202 : 7 : SyncPostCheckpoint(void)
203 : : {
204 : 7 : int absorb_counter;
205 : 7 : ListCell *lc;
206 : :
207 : 7 : absorb_counter = UNLINKS_PER_ABSORB;
208 [ - + # # : 7 : foreach(lc, pendingUnlinks)
+ - ]
209 : : {
210 : 0 : PendingUnlinkEntry *entry = (PendingUnlinkEntry *) lfirst(lc);
211 : 0 : char path[MAXPGPATH];
212 : :
213 : : /* Skip over any canceled entries */
214 [ # # ]: 0 : if (entry->canceled)
215 : 0 : continue;
216 : :
217 : : /*
218 : : * New entries are appended to the end, so if the entry is new we've
219 : : * reached the end of old entries.
220 : : *
221 : : * Note: if just the right number of consecutive checkpoints fail, we
222 : : * could be fooled here by cycle_ctr wraparound. However, the only
223 : : * consequence is that we'd delay unlinking for one more checkpoint,
224 : : * which is perfectly tolerable.
225 : : */
226 [ # # ]: 0 : if (entry->cycle_ctr == checkpoint_cycle_ctr)
227 : 0 : break;
228 : :
229 : : /* Unlink the file */
230 : 0 : if (syncsw[entry->tag.handler].sync_unlinkfiletag(&entry->tag,
231 [ # # # # ]: 0 : path) < 0)
232 : : {
233 : : /*
234 : : * There's a race condition, when the database is dropped at the
235 : : * same time that we process the pending unlink requests. If the
236 : : * DROP DATABASE deletes the file before we do, we will get ENOENT
237 : : * here. rmtree() also has to ignore ENOENT errors, to deal with
238 : : * the possibility that we delete the file first.
239 : : */
240 [ # # ]: 0 : if (errno != ENOENT)
241 [ # # # # ]: 0 : ereport(WARNING,
242 : : (errcode_for_file_access(),
243 : : errmsg("could not remove file \"%s\": %m", path)));
244 : 0 : }
245 : :
246 : : /* Mark the list entry as canceled, just in case */
247 : 0 : entry->canceled = true;
248 : :
249 : : /*
250 : : * As in ProcessSyncRequests, we don't want to stop absorbing fsync
251 : : * requests for a long time when there are many deletions to be done.
252 : : * We can safely call AbsorbSyncRequests() at this point in the loop.
253 : : */
254 [ # # ]: 0 : if (--absorb_counter <= 0)
255 : : {
256 : 0 : AbsorbSyncRequests();
257 : 0 : absorb_counter = UNLINKS_PER_ABSORB;
258 : 0 : }
259 [ # # # ]: 0 : }
260 : :
261 : : /*
262 : : * If we reached the end of the list, we can just remove the whole list
263 : : * (remembering to pfree all the PendingUnlinkEntry objects). Otherwise,
264 : : * we must keep the entries at or after "lc".
265 : : */
266 [ - + ]: 7 : if (lc == NULL)
267 : : {
268 : 7 : list_free_deep(pendingUnlinks);
269 : 7 : pendingUnlinks = NIL;
270 : 7 : }
271 : : else
272 : : {
273 : 0 : int ntodelete = list_cell_number(pendingUnlinks, lc);
274 : :
275 [ # # ]: 0 : for (int i = 0; i < ntodelete; i++)
276 : 0 : pfree(list_nth(pendingUnlinks, i));
277 : :
278 : 0 : pendingUnlinks = list_delete_first_n(pendingUnlinks, ntodelete);
279 : 0 : }
280 : 7 : }
281 : :
282 : : /*
283 : : * ProcessSyncRequests() -- Process queued fsync requests.
284 : : */
285 : : void
286 : 7 : ProcessSyncRequests(void)
287 : : {
288 : : static bool sync_in_progress = false;
289 : :
290 : 7 : HASH_SEQ_STATUS hstat;
291 : 7 : PendingFsyncEntry *entry;
292 : 7 : int absorb_counter;
293 : :
294 : : /* Statistics on sync times */
295 : 7 : int processed = 0;
296 : 7 : instr_time sync_start,
297 : : sync_end,
298 : : sync_diff;
299 : 7 : uint64 elapsed;
300 : 7 : uint64 longest = 0;
301 : 7 : uint64 total_elapsed = 0;
302 : :
303 : : /*
304 : : * This is only called during checkpoints, and checkpoints should only
305 : : * occur in processes that have created a pendingOps.
306 : : */
307 [ + - ]: 7 : if (!pendingOps)
308 [ # # # # ]: 0 : elog(ERROR, "cannot sync without a pendingOps table");
309 : :
310 : : /*
311 : : * If we are in the checkpointer, the sync had better include all fsync
312 : : * requests that were queued by backends up to this point. The tightest
313 : : * race condition that could occur is that a buffer that must be written
314 : : * and fsync'd for the checkpoint could have been dumped by a backend just
315 : : * before it was visited by BufferSync(). We know the backend will have
316 : : * queued an fsync request before clearing the buffer's dirtybit, so we
317 : : * are safe as long as we do an Absorb after completing BufferSync().
318 : : */
319 : 7 : AbsorbSyncRequests();
320 : :
321 : : /*
322 : : * To avoid excess fsync'ing (in the worst case, maybe a never-terminating
323 : : * checkpoint), we want to ignore fsync requests that are entered into the
324 : : * hashtable after this point --- they should be processed next time,
325 : : * instead. We use sync_cycle_ctr to tell old entries apart from new
326 : : * ones: new ones will have cycle_ctr equal to the incremented value of
327 : : * sync_cycle_ctr.
328 : : *
329 : : * In normal circumstances, all entries present in the table at this point
330 : : * will have cycle_ctr exactly equal to the current (about to be old)
331 : : * value of sync_cycle_ctr. However, if we fail partway through the
332 : : * fsync'ing loop, then older values of cycle_ctr might remain when we
333 : : * come back here to try again. Repeated checkpoint failures would
334 : : * eventually wrap the counter around to the point where an old entry
335 : : * might appear new, causing us to skip it, possibly allowing a checkpoint
336 : : * to succeed that should not have. To forestall wraparound, any time the
337 : : * previous ProcessSyncRequests() failed to complete, run through the
338 : : * table and forcibly set cycle_ctr = sync_cycle_ctr.
339 : : *
340 : : * Think not to merge this loop with the main loop, as the problem is
341 : : * exactly that that loop may fail before having visited all the entries.
342 : : * From a performance point of view it doesn't matter anyway, as this path
343 : : * will never be taken in a system that's functioning normally.
344 : : */
345 [ + - ]: 7 : if (sync_in_progress)
346 : : {
347 : : /* prior try failed, so update any stale cycle_ctr values */
348 : 0 : hash_seq_init(&hstat, pendingOps);
349 [ # # ]: 0 : while ((entry = (PendingFsyncEntry *) hash_seq_search(&hstat)) != NULL)
350 : : {
351 : 0 : entry->cycle_ctr = sync_cycle_ctr;
352 : : }
353 : 0 : }
354 : :
355 : : /* Advance counter so that new hashtable entries are distinguishable */
356 : 7 : sync_cycle_ctr++;
357 : :
358 : : /* Set flag to detect failure if we don't reach the end of the loop */
359 : 7 : sync_in_progress = true;
360 : :
361 : : /* Now scan the hashtable for fsync requests to process */
362 : 7 : absorb_counter = FSYNCS_PER_ABSORB;
363 : 7 : hash_seq_init(&hstat, pendingOps);
364 [ + + ]: 913 : while ((entry = (PendingFsyncEntry *) hash_seq_search(&hstat)) != NULL)
365 : : {
366 : 906 : int failures;
367 : :
368 : : /*
369 : : * If the entry is new then don't process it this time; it is new.
370 : : * Note "continue" bypasses the hash-remove call at the bottom of the
371 : : * loop.
372 : : */
373 [ - + ]: 906 : if (entry->cycle_ctr == sync_cycle_ctr)
374 : 0 : continue;
375 : :
376 : : /* Else assert we haven't missed it */
377 [ + - ]: 906 : Assert((CycleCtr) (entry->cycle_ctr + 1) == sync_cycle_ctr);
378 : :
379 : : /*
380 : : * If fsync is off then we don't have to bother opening the file at
381 : : * all. (We delay checking until this point so that changing fsync on
382 : : * the fly behaves sensibly.)
383 : : */
384 [ + - ]: 906 : if (enableFsync)
385 : : {
386 : : /*
387 : : * If in checkpointer, we want to absorb pending requests every so
388 : : * often to prevent overflow of the fsync request queue. It is
389 : : * unspecified whether newly-added entries will be visited by
390 : : * hash_seq_search, but we don't care since we don't need to
391 : : * process them anyway.
392 : : */
393 [ # # ]: 0 : if (--absorb_counter <= 0)
394 : : {
395 : 0 : AbsorbSyncRequests();
396 : 0 : absorb_counter = FSYNCS_PER_ABSORB;
397 : 0 : }
398 : :
399 : : /*
400 : : * The fsync table could contain requests to fsync segments that
401 : : * have been deleted (unlinked) by the time we get to them. Rather
402 : : * than just hoping an ENOENT (or EACCES on Windows) error can be
403 : : * ignored, what we do on error is absorb pending requests and
404 : : * then retry. Since mdunlink() queues a "cancel" message before
405 : : * actually unlinking, the fsync request is guaranteed to be
406 : : * marked canceled after the absorb if it really was this case.
407 : : * DROP DATABASE likewise has to tell us to forget fsync requests
408 : : * before it starts deletions.
409 : : */
410 [ # # ]: 0 : for (failures = 0; !entry->canceled; failures++)
411 : : {
412 : 0 : char path[MAXPGPATH];
413 : :
414 : 0 : INSTR_TIME_SET_CURRENT(sync_start);
415 : 0 : if (syncsw[entry->tag.handler].sync_syncfiletag(&entry->tag,
416 [ # # # # ]: 0 : path) == 0)
417 : : {
418 : : /* Success; update statistics about sync timing */
419 : 0 : INSTR_TIME_SET_CURRENT(sync_end);
420 : 0 : sync_diff = sync_end;
421 : 0 : INSTR_TIME_SUBTRACT(sync_diff, sync_start);
422 : 0 : elapsed = INSTR_TIME_GET_MICROSEC(sync_diff);
423 [ # # ]: 0 : if (elapsed > longest)
424 : 0 : longest = elapsed;
425 : 0 : total_elapsed += elapsed;
426 : 0 : processed++;
427 : :
428 [ # # ]: 0 : if (log_checkpoints)
429 [ # # # # ]: 0 : elog(DEBUG1, "checkpoint sync: number=%d file=%s time=%.3f ms",
430 : : processed,
431 : : path,
432 : : (double) elapsed / 1000);
433 : :
434 : 0 : break; /* out of retry loop */
435 : : }
436 : :
437 : : /*
438 : : * It is possible that the relation has been dropped or
439 : : * truncated since the fsync request was entered. Therefore,
440 : : * allow ENOENT, but only if we didn't fail already on this
441 : : * file.
442 : : */
443 [ # # # # ]: 0 : if (!FILE_POSSIBLY_DELETED(errno) || failures > 0)
444 [ # # # # : 0 : ereport(data_sync_elevel(ERROR),
# # ]
445 : : (errcode_for_file_access(),
446 : : errmsg("could not fsync file \"%s\": %m",
447 : : path)));
448 : : else
449 [ # # # # ]: 0 : ereport(DEBUG1,
450 : : (errcode_for_file_access(),
451 : : errmsg_internal("could not fsync file \"%s\" but retrying: %m",
452 : : path)));
453 : :
454 : : /*
455 : : * Absorb incoming requests and check to see if a cancel
456 : : * arrived for this relation fork.
457 : : */
458 : 0 : AbsorbSyncRequests();
459 : 0 : absorb_counter = FSYNCS_PER_ABSORB; /* might as well... */
460 [ # # ]: 0 : } /* end retry loop */
461 : 0 : }
462 : :
463 : : /* We are done with this entry, remove it */
464 [ + - ]: 906 : if (hash_search(pendingOps, &entry->tag, HASH_REMOVE, NULL) == NULL)
465 [ # # # # ]: 0 : elog(ERROR, "pendingOps corrupted");
466 [ - + ]: 906 : } /* end loop over hashtable entries */
467 : :
468 : : /* Return sync performance metrics for report at checkpoint end */
469 : 7 : CheckpointStats.ckpt_sync_rels = processed;
470 : 7 : CheckpointStats.ckpt_longest_sync = longest;
471 : 7 : CheckpointStats.ckpt_agg_sync_time = total_elapsed;
472 : :
473 : : /* Flag successful completion of ProcessSyncRequests */
474 : 7 : sync_in_progress = false;
475 : 7 : }
476 : :
477 : : /*
478 : : * RememberSyncRequest() -- callback from checkpointer side of sync request
479 : : *
480 : : * We stuff fsync requests into the local hash table for execution
481 : : * during the checkpointer's next checkpoint. UNLINK requests go into a
482 : : * separate linked list, however, because they get processed separately.
483 : : *
484 : : * See sync.h for more information on the types of sync requests supported.
485 : : */
486 : : void
487 : 9996 : RememberSyncRequest(const FileTag *ftag, SyncRequestType type)
488 : : {
489 [ + - ]: 9996 : Assert(pendingOps);
490 : :
491 [ - + ]: 9996 : if (type == SYNC_FORGET_REQUEST)
492 : : {
493 : 0 : PendingFsyncEntry *entry;
494 : :
495 : : /* Cancel previously entered request */
496 : 0 : entry = (PendingFsyncEntry *) hash_search(pendingOps,
497 : 0 : ftag,
498 : : HASH_FIND,
499 : : NULL);
500 [ # # ]: 0 : if (entry != NULL)
501 : 0 : entry->canceled = true;
502 : 0 : }
503 [ - + ]: 9996 : else if (type == SYNC_FILTER_REQUEST)
504 : : {
505 : 0 : HASH_SEQ_STATUS hstat;
506 : 0 : PendingFsyncEntry *pfe;
507 : 0 : ListCell *cell;
508 : :
509 : : /* Cancel matching fsync requests */
510 : 0 : hash_seq_init(&hstat, pendingOps);
511 [ # # ]: 0 : while ((pfe = (PendingFsyncEntry *) hash_seq_search(&hstat)) != NULL)
512 : : {
513 [ # # # # ]: 0 : if (pfe->tag.handler == ftag->handler &&
514 : 0 : syncsw[ftag->handler].sync_filetagmatches(ftag, &pfe->tag))
515 : 0 : pfe->canceled = true;
516 : : }
517 : :
518 : : /* Cancel matching unlink requests */
519 [ # # # # : 0 : foreach(cell, pendingUnlinks)
# # ]
520 : : {
521 : 0 : PendingUnlinkEntry *pue = (PendingUnlinkEntry *) lfirst(cell);
522 : :
523 [ # # # # ]: 0 : if (pue->tag.handler == ftag->handler &&
524 : 0 : syncsw[ftag->handler].sync_filetagmatches(ftag, &pue->tag))
525 : 0 : pue->canceled = true;
526 : 0 : }
527 : 0 : }
528 [ - + ]: 9996 : else if (type == SYNC_UNLINK_REQUEST)
529 : : {
530 : : /* Unlink request: put it in the linked list */
531 : 0 : MemoryContext oldcxt = MemoryContextSwitchTo(pendingOpsCxt);
532 : 0 : PendingUnlinkEntry *entry;
533 : :
534 : 0 : entry = palloc_object(PendingUnlinkEntry);
535 : 0 : entry->tag = *ftag;
536 : 0 : entry->cycle_ctr = checkpoint_cycle_ctr;
537 : 0 : entry->canceled = false;
538 : :
539 : 0 : pendingUnlinks = lappend(pendingUnlinks, entry);
540 : :
541 : 0 : MemoryContextSwitchTo(oldcxt);
542 : 0 : }
543 : : else
544 : : {
545 : : /* Normal case: enter a request to fsync this segment */
546 : 9996 : MemoryContext oldcxt = MemoryContextSwitchTo(pendingOpsCxt);
547 : 9996 : PendingFsyncEntry *entry;
548 : 9996 : bool found;
549 : :
550 [ + - ]: 9996 : Assert(type == SYNC_REQUEST);
551 : :
552 : 19992 : entry = (PendingFsyncEntry *) hash_search(pendingOps,
553 : 9996 : ftag,
554 : : HASH_ENTER,
555 : : &found);
556 : : /* if new entry, or was previously canceled, initialize it */
557 [ + + - + ]: 9996 : if (!found || entry->canceled)
558 : : {
559 : 906 : entry->cycle_ctr = sync_cycle_ctr;
560 : 906 : entry->canceled = false;
561 : 906 : }
562 : :
563 : : /*
564 : : * NB: it's intentional that we don't change cycle_ctr if the entry
565 : : * already exists. The cycle_ctr must represent the oldest fsync
566 : : * request that could be in the entry.
567 : : */
568 : :
569 : 9996 : MemoryContextSwitchTo(oldcxt);
570 : 9996 : }
571 : 9996 : }
572 : :
573 : : /*
574 : : * Register the sync request locally, or forward it to the checkpointer.
575 : : *
576 : : * If retryOnError is true, we'll keep trying if there is no space in the
577 : : * queue. Return true if we succeeded, or false if there wasn't space.
578 : : */
579 : : bool
580 : 77976 : RegisterSyncRequest(const FileTag *ftag, SyncRequestType type,
581 : : bool retryOnError)
582 : : {
583 : 77976 : bool ret;
584 : :
585 [ + + ]: 77976 : if (pendingOps != NULL)
586 : : {
587 : : /* standalone backend or startup process: fsync state is local */
588 : 6371 : RememberSyncRequest(ftag, type);
589 : 6371 : return true;
590 : : }
591 : :
592 : 71605 : for (;;)
593 : : {
594 : : /*
595 : : * Notify the checkpointer about it. If we fail to queue a message in
596 : : * retryOnError mode, we have to sleep and try again ... ugly, but
597 : : * hopefully won't happen often.
598 : : *
599 : : * XXX should we CHECK_FOR_INTERRUPTS in this loop? Escaping with an
600 : : * error in the case of SYNC_UNLINK_REQUEST would leave the
601 : : * no-longer-used file still present on disk, which would be bad, so
602 : : * I'm inclined to assume that the checkpointer will always empty the
603 : : * queue soon.
604 : : */
605 : 71605 : ret = ForwardSyncRequest(ftag, type);
606 : :
607 : : /*
608 : : * If we are successful in queueing the request, or we failed and were
609 : : * instructed not to retry on error, break.
610 : : */
611 [ - + # # : 71605 : if (ret || (!ret && !retryOnError))
# # ]
612 : 71605 : break;
613 : :
614 : 0 : WaitLatch(NULL, WL_EXIT_ON_PM_DEATH | WL_TIMEOUT, 10,
615 : : WAIT_EVENT_REGISTER_SYNC_REQUEST);
616 : : }
617 : :
618 : 71605 : return ret;
619 : 77976 : }
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