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1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * slru.c
4 : : * Simple LRU buffering for wrap-around-able permanent metadata
5 : : *
6 : : * This module is used to maintain various pieces of transaction status
7 : : * indexed by TransactionId (such as commit status, parent transaction ID,
8 : : * commit timestamp), as well as storage for multixacts, serializable
9 : : * isolation locks and NOTIFY traffic. Extensions can define their own
10 : : * SLRUs, too.
11 : : *
12 : : * Under ordinary circumstances we expect that write traffic will occur
13 : : * mostly to the latest page (and to the just-prior page, soon after a
14 : : * page transition). Read traffic will probably touch a larger span of
15 : : * pages, but a relatively small number of buffers should be sufficient.
16 : : *
17 : : * We use a simple least-recently-used scheme to manage a pool of shared
18 : : * page buffers, split in banks by the lowest bits of the page number, and
19 : : * the management algorithm only processes the bank to which the desired
20 : : * page belongs, so a linear search is sufficient; there's no need for a
21 : : * hashtable or anything fancy. The algorithm is straight LRU except that
22 : : * we will never swap out the latest page (since we know it's going to be
23 : : * hit again eventually).
24 : : *
25 : : * We use per-bank control LWLocks to protect the shared data structures,
26 : : * plus per-buffer LWLocks that synchronize I/O for each buffer. The
27 : : * bank's control lock must be held to examine or modify any of the bank's
28 : : * shared state. A process that is reading in or writing out a page
29 : : * buffer does not hold the control lock, only the per-buffer lock for the
30 : : * buffer it is working on. One exception is latest_page_number, which is
31 : : * read and written using atomic ops.
32 : : *
33 : : * "Holding the bank control lock" means exclusive lock in all cases
34 : : * except for SimpleLruReadPage_ReadOnly(); see comments for
35 : : * SlruRecentlyUsed() for the implications of that.
36 : : *
37 : : * When initiating I/O on a buffer, we acquire the per-buffer lock exclusively
38 : : * before releasing the control lock. The per-buffer lock is released after
39 : : * completing the I/O, re-acquiring the control lock, and updating the shared
40 : : * state. (Deadlock is not possible here, because we never try to initiate
41 : : * I/O when someone else is already doing I/O on the same buffer.)
42 : : * To wait for I/O to complete, release the control lock, acquire the
43 : : * per-buffer lock in shared mode, immediately release the per-buffer lock,
44 : : * reacquire the control lock, and then recheck state (since arbitrary things
45 : : * could have happened while we didn't have the lock).
46 : : *
47 : : * As with the regular buffer manager, it is possible for another process
48 : : * to re-dirty a page that is currently being written out. This is handled
49 : : * by re-setting the page's page_dirty flag.
50 : : *
51 : : *
52 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
53 : : * Portions Copyright (c) 1994, Regents of the University of California
54 : : *
55 : : * src/backend/access/transam/slru.c
56 : : *
57 : : *-------------------------------------------------------------------------
58 : : */
59 : : #include "postgres.h"
60 : :
61 : : #include <fcntl.h>
62 : : #include <sys/stat.h>
63 : : #include <unistd.h>
64 : :
65 : : #include "access/slru.h"
66 : : #include "access/transam.h"
67 : : #include "access/xlog.h"
68 : : #include "access/xlogutils.h"
69 : : #include "miscadmin.h"
70 : : #include "pgstat.h"
71 : : #include "storage/fd.h"
72 : : #include "storage/shmem.h"
73 : : #include "utils/guc.h"
74 : :
75 : : /*
76 : : * Converts segment number to the filename of the segment.
77 : : *
78 : : * "path" should point to a buffer at least MAXPGPATH characters long.
79 : : *
80 : : * If ctl->long_segment_names is true, segno can be in the range [0, 2^60-1].
81 : : * The resulting file name is made of 15 characters, e.g. dir/123456789ABCDEF.
82 : : *
83 : : * If ctl->long_segment_names is false, segno can be in the range [0, 2^24-1].
84 : : * The resulting file name is made of 4 to 6 characters, as of:
85 : : *
86 : : * dir/1234 for [0, 2^16-1]
87 : : * dir/12345 for [2^16, 2^20-1]
88 : : * dir/123456 for [2^20, 2^24-1]
89 : : */
90 : : static inline int
91 : 19 : SlruFileName(SlruCtl ctl, char *path, int64 segno)
92 : : {
93 [ + + ]: 19 : if (ctl->long_segment_names)
94 : : {
95 : : /*
96 : : * We could use 16 characters here but the disadvantage would be that
97 : : * the SLRU segments will be hard to distinguish from WAL segments.
98 : : *
99 : : * For this reason we use 15 characters. It is enough but also means
100 : : * that in the future we can't decrease SLRU_PAGES_PER_SEGMENT easily.
101 : : */
102 [ + - ]: 2 : Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFFFFFFFFFFF));
103 : 2 : return snprintf(path, MAXPGPATH, "%s/%015" PRIX64, ctl->Dir, segno);
104 : : }
105 : : else
106 : : {
107 : : /*
108 : : * Despite the fact that %04X format string is used up to 24 bit
109 : : * integers are allowed. See SlruCorrectSegmentFilenameLength()
110 : : */
111 [ + - ]: 17 : Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFF));
112 : 34 : return snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir,
113 : 17 : (unsigned int) segno);
114 : : }
115 : 19 : }
116 : :
117 : : /*
118 : : * During SimpleLruWriteAll(), we will usually not need to write more than one
119 : : * or two physical files, but we may need to write several pages per file. We
120 : : * can consolidate the I/O requests by leaving files open until control returns
121 : : * to SimpleLruWriteAll(). This data structure remembers which files are open.
122 : : */
123 : : #define MAX_WRITEALL_BUFFERS 16
124 : :
125 : : typedef struct SlruWriteAllData
126 : : {
127 : : int num_files; /* # files actually open */
128 : : int fd[MAX_WRITEALL_BUFFERS]; /* their FD's */
129 : : int64 segno[MAX_WRITEALL_BUFFERS]; /* their log seg#s */
130 : : } SlruWriteAllData;
131 : :
132 : : typedef struct SlruWriteAllData *SlruWriteAll;
133 : :
134 : :
135 : : /*
136 : : * Bank size for the slot array. Pages are assigned a bank according to their
137 : : * page number, with each bank being this size. We want a power of 2 so that
138 : : * we can determine the bank number for a page with just bit shifting; we also
139 : : * want to keep the bank size small so that LRU victim search is fast. 16
140 : : * buffers per bank seems a good number.
141 : : */
142 : : #define SLRU_BANK_BITSHIFT 4
143 : : #define SLRU_BANK_SIZE (1 << SLRU_BANK_BITSHIFT)
144 : :
145 : : /*
146 : : * Macro to get the bank number to which the slot belongs.
147 : : */
148 : : #define SlotGetBankNumber(slotno) ((slotno) >> SLRU_BANK_BITSHIFT)
149 : :
150 : :
151 : : /*
152 : : * Populate a file tag describing a segment file. We only use the segment
153 : : * number, since we can derive everything else we need by having separate
154 : : * sync handler functions for clog, multixact etc.
155 : : */
156 : : #define INIT_SLRUFILETAG(a,xx_handler,xx_segno) \
157 : : ( \
158 : : memset(&(a), 0, sizeof(FileTag)), \
159 : : (a).handler = (xx_handler), \
160 : : (a).segno = (xx_segno) \
161 : : )
162 : :
163 : : /* Saved info for SlruReportIOError */
164 : : typedef enum
165 : : {
166 : : SLRU_OPEN_FAILED,
167 : : SLRU_SEEK_FAILED,
168 : : SLRU_READ_FAILED,
169 : : SLRU_WRITE_FAILED,
170 : : SLRU_FSYNC_FAILED,
171 : : SLRU_CLOSE_FAILED,
172 : : } SlruErrorCause;
173 : :
174 : : static SlruErrorCause slru_errcause;
175 : : static int slru_errno;
176 : :
177 : :
178 : : static void SimpleLruZeroLSNs(SlruCtl ctl, int slotno);
179 : : static void SimpleLruWaitIO(SlruCtl ctl, int slotno);
180 : : static void SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata);
181 : : static bool SlruPhysicalReadPage(SlruCtl ctl, int64 pageno, int slotno);
182 : : static bool SlruPhysicalWritePage(SlruCtl ctl, int64 pageno, int slotno,
183 : : SlruWriteAll fdata);
184 : : static void SlruReportIOError(SlruCtl ctl, int64 pageno, TransactionId xid);
185 : : static int SlruSelectLRUPage(SlruCtl ctl, int64 pageno);
186 : :
187 : : static bool SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename,
188 : : int64 segpage, void *data);
189 : : static void SlruInternalDeleteSegment(SlruCtl ctl, int64 segno);
190 : : static inline void SlruRecentlyUsed(SlruShared shared, int slotno);
191 : :
192 : :
193 : : /*
194 : : * Initialization of shared memory
195 : : */
196 : :
197 : : Size
198 : 147 : SimpleLruShmemSize(int nslots, int nlsns)
199 : : {
200 : 147 : int nbanks = nslots / SLRU_BANK_SIZE;
201 : 147 : Size sz;
202 : :
203 [ + - ]: 147 : Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
204 [ + - ]: 147 : Assert(nslots % SLRU_BANK_SIZE == 0);
205 : :
206 : : /* we assume nslots isn't so large as to risk overflow */
207 : 147 : sz = MAXALIGN(sizeof(SlruSharedData));
208 : 147 : sz += MAXALIGN(nslots * sizeof(char *)); /* page_buffer[] */
209 : 147 : sz += MAXALIGN(nslots * sizeof(SlruPageStatus)); /* page_status[] */
210 : 147 : sz += MAXALIGN(nslots * sizeof(bool)); /* page_dirty[] */
211 : 147 : sz += MAXALIGN(nslots * sizeof(int64)); /* page_number[] */
212 : 147 : sz += MAXALIGN(nslots * sizeof(int)); /* page_lru_count[] */
213 : 147 : sz += MAXALIGN(nslots * sizeof(LWLockPadded)); /* buffer_locks[] */
214 : 147 : sz += MAXALIGN(nbanks * sizeof(LWLockPadded)); /* bank_locks[] */
215 : 147 : sz += MAXALIGN(nbanks * sizeof(int)); /* bank_cur_lru_count[] */
216 : :
217 [ + + ]: 147 : if (nlsns > 0)
218 : 21 : sz += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr)); /* group_lsn[] */
219 : :
220 : 294 : return BUFFERALIGN(sz) + BLCKSZ * nslots;
221 : 147 : }
222 : :
223 : : /*
224 : : * Determine a number of SLRU buffers to use.
225 : : *
226 : : * We simply divide shared_buffers by the divisor given and cap
227 : : * that at the maximum given; but always at least SLRU_BANK_SIZE.
228 : : * Round down to the nearest multiple of SLRU_BANK_SIZE.
229 : : */
230 : : int
231 : 45 : SimpleLruAutotuneBuffers(int divisor, int max)
232 : : {
233 [ + + - + : 45 : return Min(max - (max % SLRU_BANK_SIZE),
+ + ]
234 : : Max(SLRU_BANK_SIZE,
235 : : NBuffers / divisor - (NBuffers / divisor) % SLRU_BANK_SIZE));
236 : : }
237 : :
238 : : /*
239 : : * Initialize, or attach to, a simple LRU cache in shared memory.
240 : : *
241 : : * ctl: address of local (unshared) control structure.
242 : : * name: name of SLRU. (This is user-visible, pick with care!)
243 : : * nslots: number of page slots to use.
244 : : * nlsns: number of LSN groups per page (set to zero if not relevant).
245 : : * subdir: PGDATA-relative subdirectory that will contain the files.
246 : : * buffer_tranche_id: tranche ID to use for the SLRU's per-buffer LWLocks.
247 : : * bank_tranche_id: tranche ID to use for the bank LWLocks.
248 : : * sync_handler: which set of functions to use to handle sync requests
249 : : * long_segment_names: use short or long segment names
250 : : */
251 : : void
252 : 42 : SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
253 : : const char *subdir, int buffer_tranche_id, int bank_tranche_id,
254 : : SyncRequestHandler sync_handler, bool long_segment_names)
255 : : {
256 : 42 : SlruShared shared;
257 : 42 : bool found;
258 : 42 : int nbanks = nslots / SLRU_BANK_SIZE;
259 : :
260 [ + - ]: 42 : Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
261 : :
262 : 84 : shared = (SlruShared) ShmemInitStruct(name,
263 : 42 : SimpleLruShmemSize(nslots, nlsns),
264 : : &found);
265 : :
266 [ - + ]: 42 : if (!IsUnderPostmaster)
267 : : {
268 : : /* Initialize locks and shared memory area */
269 : 42 : char *ptr;
270 : 42 : Size offset;
271 : :
272 [ + - ]: 42 : Assert(!found);
273 : :
274 : 42 : memset(shared, 0, sizeof(SlruSharedData));
275 : :
276 : 42 : shared->num_slots = nslots;
277 : 42 : shared->lsn_groups_per_page = nlsns;
278 : :
279 : 42 : pg_atomic_init_u64(&shared->latest_page_number, 0);
280 : :
281 : 42 : shared->slru_stats_idx = pgstat_get_slru_index(name);
282 : :
283 : 42 : ptr = (char *) shared;
284 : 42 : offset = MAXALIGN(sizeof(SlruSharedData));
285 : 42 : shared->page_buffer = (char **) (ptr + offset);
286 : 42 : offset += MAXALIGN(nslots * sizeof(char *));
287 : 42 : shared->page_status = (SlruPageStatus *) (ptr + offset);
288 : 42 : offset += MAXALIGN(nslots * sizeof(SlruPageStatus));
289 : 42 : shared->page_dirty = (bool *) (ptr + offset);
290 : 42 : offset += MAXALIGN(nslots * sizeof(bool));
291 : 42 : shared->page_number = (int64 *) (ptr + offset);
292 : 42 : offset += MAXALIGN(nslots * sizeof(int64));
293 : 42 : shared->page_lru_count = (int *) (ptr + offset);
294 : 42 : offset += MAXALIGN(nslots * sizeof(int));
295 : :
296 : : /* Initialize LWLocks */
297 : 42 : shared->buffer_locks = (LWLockPadded *) (ptr + offset);
298 : 42 : offset += MAXALIGN(nslots * sizeof(LWLockPadded));
299 : 42 : shared->bank_locks = (LWLockPadded *) (ptr + offset);
300 : 42 : offset += MAXALIGN(nbanks * sizeof(LWLockPadded));
301 : 42 : shared->bank_cur_lru_count = (int *) (ptr + offset);
302 : 42 : offset += MAXALIGN(nbanks * sizeof(int));
303 : :
304 [ + + ]: 42 : if (nlsns > 0)
305 : : {
306 : 6 : shared->group_lsn = (XLogRecPtr *) (ptr + offset);
307 : 6 : offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));
308 : 6 : }
309 : :
310 : 42 : ptr += BUFFERALIGN(offset);
311 [ + + ]: 1146 : for (int slotno = 0; slotno < nslots; slotno++)
312 : : {
313 : 2208 : LWLockInitialize(&shared->buffer_locks[slotno].lock,
314 : 1104 : buffer_tranche_id);
315 : :
316 : 1104 : shared->page_buffer[slotno] = ptr;
317 : 1104 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
318 : 1104 : shared->page_dirty[slotno] = false;
319 : 1104 : shared->page_lru_count[slotno] = 0;
320 : 1104 : ptr += BLCKSZ;
321 : 1104 : }
322 : :
323 : : /* Initialize the slot banks. */
324 [ + + ]: 111 : for (int bankno = 0; bankno < nbanks; bankno++)
325 : : {
326 : 69 : LWLockInitialize(&shared->bank_locks[bankno].lock, bank_tranche_id);
327 : 69 : shared->bank_cur_lru_count[bankno] = 0;
328 : 69 : }
329 : :
330 : : /* Should fit to estimated shmem size */
331 [ + - ]: 42 : Assert(ptr - (char *) shared <= SimpleLruShmemSize(nslots, nlsns));
332 : 42 : }
333 : : else
334 : : {
335 [ # # ]: 0 : Assert(found);
336 [ # # ]: 0 : Assert(shared->num_slots == nslots);
337 : : }
338 : :
339 : : /*
340 : : * Initialize the unshared control struct, including directory path. We
341 : : * assume caller set PagePrecedes.
342 : : */
343 : 42 : ctl->shared = shared;
344 : 42 : ctl->sync_handler = sync_handler;
345 : 42 : ctl->long_segment_names = long_segment_names;
346 : 42 : ctl->nbanks = nbanks;
347 : 42 : strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir));
348 : 42 : }
349 : :
350 : : /*
351 : : * Helper function for GUC check_hook to check whether slru buffers are in
352 : : * multiples of SLRU_BANK_SIZE.
353 : : */
354 : : bool
355 : 60 : check_slru_buffers(const char *name, int *newval)
356 : : {
357 : : /* Valid values are multiples of SLRU_BANK_SIZE */
358 [ - + ]: 60 : if (*newval % SLRU_BANK_SIZE == 0)
359 : 60 : return true;
360 : :
361 : 0 : GUC_check_errdetail("\"%s\" must be a multiple of %d.", name,
362 : : SLRU_BANK_SIZE);
363 : 0 : return false;
364 : 60 : }
365 : :
366 : : /*
367 : : * Initialize (or reinitialize) a page to zeroes.
368 : : *
369 : : * The page is not actually written, just set up in shared memory.
370 : : * The slot number of the new page is returned.
371 : : *
372 : : * Bank lock must be held at entry, and will be held at exit.
373 : : */
374 : : int
375 : 25 : SimpleLruZeroPage(SlruCtl ctl, int64 pageno)
376 : : {
377 : 25 : SlruShared shared = ctl->shared;
378 : 25 : int slotno;
379 : :
380 [ + - ]: 25 : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
381 : :
382 : : /* Find a suitable buffer slot for the page */
383 : 25 : slotno = SlruSelectLRUPage(ctl, pageno);
384 [ + + + - : 25 : Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
+ - ]
385 : : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
386 : : !shared->page_dirty[slotno]) ||
387 : : shared->page_number[slotno] == pageno);
388 : :
389 : : /* Mark the slot as containing this page */
390 : 25 : shared->page_number[slotno] = pageno;
391 : 25 : shared->page_status[slotno] = SLRU_PAGE_VALID;
392 : 25 : shared->page_dirty[slotno] = true;
393 : 25 : SlruRecentlyUsed(shared, slotno);
394 : :
395 : : /* Set the buffer to zeroes */
396 [ + - + - : 25 : MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
+ - + - #
# ]
397 : :
398 : : /* Set the LSNs for this new page to zero */
399 : 25 : SimpleLruZeroLSNs(ctl, slotno);
400 : :
401 : : /*
402 : : * Assume this page is now the latest active page.
403 : : *
404 : : * Note that because both this routine and SlruSelectLRUPage run with a
405 : : * SLRU bank lock held, it is not possible for this to be zeroing a page
406 : : * that SlruSelectLRUPage is going to evict simultaneously. Therefore,
407 : : * there's no memory barrier here.
408 : : */
409 : 25 : pg_atomic_write_u64(&shared->latest_page_number, pageno);
410 : :
411 : : /* update the stats counter of zeroed pages */
412 : 25 : pgstat_count_slru_blocks_zeroed(shared->slru_stats_idx);
413 : :
414 : 50 : return slotno;
415 : 25 : }
416 : :
417 : : /*
418 : : * Zero all the LSNs we store for this slru page.
419 : : *
420 : : * This should be called each time we create a new page, and each time we read
421 : : * in a page from disk into an existing buffer. (Such an old page cannot
422 : : * have any interesting LSNs, since we'd have flushed them before writing
423 : : * the page in the first place.)
424 : : *
425 : : * This assumes that InvalidXLogRecPtr is bitwise-all-0.
426 : : */
427 : : static void
428 : 29 : SimpleLruZeroLSNs(SlruCtl ctl, int slotno)
429 : : {
430 : 29 : SlruShared shared = ctl->shared;
431 : :
432 [ + + ]: 29 : if (shared->lsn_groups_per_page > 0)
433 [ + - + - : 5 : MemSet(&shared->group_lsn[slotno * shared->lsn_groups_per_page], 0,
+ - + - #
# ]
434 : : shared->lsn_groups_per_page * sizeof(XLogRecPtr));
435 : 29 : }
436 : :
437 : : /*
438 : : * This is a convenience wrapper for the common case of zeroing a page and
439 : : * immediately flushing it to disk.
440 : : *
441 : : * SLRU bank lock is acquired and released here.
442 : : */
443 : : void
444 : 4 : SimpleLruZeroAndWritePage(SlruCtl ctl, int64 pageno)
445 : : {
446 : 4 : int slotno;
447 : 4 : LWLock *lock;
448 : :
449 : 4 : lock = SimpleLruGetBankLock(ctl, pageno);
450 : 4 : LWLockAcquire(lock, LW_EXCLUSIVE);
451 : :
452 : : /* Create and zero the page */
453 : 4 : slotno = SimpleLruZeroPage(ctl, pageno);
454 : :
455 : : /* Make sure it's written out */
456 : 4 : SimpleLruWritePage(ctl, slotno);
457 [ + - ]: 4 : Assert(!ctl->shared->page_dirty[slotno]);
458 : :
459 : 4 : LWLockRelease(lock);
460 : 4 : }
461 : :
462 : : /*
463 : : * Wait for any active I/O on a page slot to finish. (This does not
464 : : * guarantee that new I/O hasn't been started before we return, though.
465 : : * In fact the slot might not even contain the same page anymore.)
466 : : *
467 : : * Bank lock must be held at entry, and will be held at exit.
468 : : */
469 : : static void
470 : 0 : SimpleLruWaitIO(SlruCtl ctl, int slotno)
471 : : {
472 : 0 : SlruShared shared = ctl->shared;
473 : 0 : int bankno = SlotGetBankNumber(slotno);
474 : :
475 [ # # ]: 0 : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
476 : :
477 : : /* See notes at top of file */
478 : 0 : LWLockRelease(&shared->bank_locks[bankno].lock);
479 : 0 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED);
480 : 0 : LWLockRelease(&shared->buffer_locks[slotno].lock);
481 : 0 : LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
482 : :
483 : : /*
484 : : * If the slot is still in an io-in-progress state, then either someone
485 : : * already started a new I/O on the slot, or a previous I/O failed and
486 : : * neglected to reset the page state. That shouldn't happen, really, but
487 : : * it seems worth a few extra cycles to check and recover from it. We can
488 : : * cheaply test for failure by seeing if the buffer lock is still held (we
489 : : * assume that transaction abort would release the lock).
490 : : */
491 [ # # # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
492 : 0 : shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS)
493 : : {
494 [ # # ]: 0 : if (LWLockConditionalAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED))
495 : : {
496 : : /* indeed, the I/O must have failed */
497 [ # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS)
498 : 0 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
499 : : else /* write_in_progress */
500 : : {
501 : 0 : shared->page_status[slotno] = SLRU_PAGE_VALID;
502 : 0 : shared->page_dirty[slotno] = true;
503 : : }
504 : 0 : LWLockRelease(&shared->buffer_locks[slotno].lock);
505 : 0 : }
506 : 0 : }
507 : 0 : }
508 : :
509 : : /*
510 : : * Find a page in a shared buffer, reading it in if necessary.
511 : : * The page number must correspond to an already-initialized page.
512 : : *
513 : : * If write_ok is true then it is OK to return a page that is in
514 : : * WRITE_IN_PROGRESS state; it is the caller's responsibility to be sure
515 : : * that modification of the page is safe. If write_ok is false then we
516 : : * will not return the page until it is not undergoing active I/O.
517 : : *
518 : : * The passed-in xid is used only for error reporting, and may be
519 : : * InvalidTransactionId if no specific xid is associated with the action.
520 : : *
521 : : * Return value is the shared-buffer slot number now holding the page.
522 : : * The buffer's LRU access info is updated.
523 : : *
524 : : * The correct bank lock must be held at entry, and will be held at exit.
525 : : */
526 : : int
527 : 22188 : SimpleLruReadPage(SlruCtl ctl, int64 pageno, bool write_ok,
528 : : TransactionId xid)
529 : : {
530 : 22188 : SlruShared shared = ctl->shared;
531 : 22188 : LWLock *banklock = SimpleLruGetBankLock(ctl, pageno);
532 : :
533 [ + - ]: 22188 : Assert(LWLockHeldByMeInMode(banklock, LW_EXCLUSIVE));
534 : :
535 : : /* Outer loop handles restart if we must wait for someone else's I/O */
536 : 22188 : for (;;)
537 : : {
538 : 22188 : int slotno;
539 : 22188 : bool ok;
540 : :
541 : : /* See if page already is in memory; if not, pick victim slot */
542 : 22188 : slotno = SlruSelectLRUPage(ctl, pageno);
543 : :
544 : : /* Did we find the page in memory? */
545 [ + + - + ]: 22188 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
546 : 22184 : shared->page_number[slotno] == pageno)
547 : : {
548 : : /*
549 : : * If page is still being read in, we must wait for I/O. Likewise
550 : : * if the page is being written and the caller said that's not OK.
551 : : */
552 [ + - # # ]: 22184 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
553 [ - + ]: 22184 : (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
554 : 0 : !write_ok))
555 : : {
556 : 0 : SimpleLruWaitIO(ctl, slotno);
557 : : /* Now we must recheck state from the top */
558 : 0 : continue;
559 : : }
560 : : /* Otherwise, it's ready to use */
561 : 22184 : SlruRecentlyUsed(shared, slotno);
562 : :
563 : : /* update the stats counter of pages found in the SLRU */
564 : 22184 : pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
565 : :
566 : 22184 : return slotno;
567 : : }
568 : :
569 : : /* We found no match; assert we selected a freeable slot */
570 [ + - # # ]: 4 : Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
571 : : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
572 : : !shared->page_dirty[slotno]));
573 : :
574 : : /* Mark the slot read-busy */
575 : 4 : shared->page_number[slotno] = pageno;
576 : 4 : shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS;
577 : 4 : shared->page_dirty[slotno] = false;
578 : :
579 : : /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
580 : 4 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
581 : :
582 : : /* Release bank lock while doing I/O */
583 : 4 : LWLockRelease(banklock);
584 : :
585 : : /* Do the read */
586 : 4 : ok = SlruPhysicalReadPage(ctl, pageno, slotno);
587 : :
588 : : /* Set the LSNs for this newly read-in page to zero */
589 : 4 : SimpleLruZeroLSNs(ctl, slotno);
590 : :
591 : : /* Re-acquire bank control lock and update page state */
592 : 4 : LWLockAcquire(banklock, LW_EXCLUSIVE);
593 : :
594 [ + - ]: 4 : Assert(shared->page_number[slotno] == pageno &&
595 : : shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS &&
596 : : !shared->page_dirty[slotno]);
597 : :
598 : 4 : shared->page_status[slotno] = ok ? SLRU_PAGE_VALID : SLRU_PAGE_EMPTY;
599 : :
600 : 4 : LWLockRelease(&shared->buffer_locks[slotno].lock);
601 : :
602 : : /* Now it's okay to ereport if we failed */
603 [ + - ]: 4 : if (!ok)
604 : 0 : SlruReportIOError(ctl, pageno, xid);
605 : :
606 : 4 : SlruRecentlyUsed(shared, slotno);
607 : :
608 : : /* update the stats counter of pages not found in SLRU */
609 : 4 : pgstat_count_slru_blocks_read(shared->slru_stats_idx);
610 : :
611 : 4 : return slotno;
612 [ - + ]: 22188 : }
613 : 22188 : }
614 : :
615 : : /*
616 : : * Find a page in a shared buffer, reading it in if necessary.
617 : : * The page number must correspond to an already-initialized page.
618 : : * The caller must intend only read-only access to the page.
619 : : *
620 : : * The passed-in xid is used only for error reporting, and may be
621 : : * InvalidTransactionId if no specific xid is associated with the action.
622 : : *
623 : : * Return value is the shared-buffer slot number now holding the page.
624 : : * The buffer's LRU access info is updated.
625 : : *
626 : : * Bank control lock must NOT be held at entry, but will be held at exit.
627 : : * It is unspecified whether the lock will be shared or exclusive.
628 : : */
629 : : int
630 : 76267 : SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
631 : : {
632 : 76267 : SlruShared shared = ctl->shared;
633 : 76267 : LWLock *banklock = SimpleLruGetBankLock(ctl, pageno);
634 : 76267 : int bankno = pageno % ctl->nbanks;
635 : 76267 : int bankstart = bankno * SLRU_BANK_SIZE;
636 : 76267 : int bankend = bankstart + SLRU_BANK_SIZE;
637 : :
638 : : /* Try to find the page while holding only shared lock */
639 : 76267 : LWLockAcquire(banklock, LW_SHARED);
640 : :
641 : : /* See if page is already in a buffer */
642 [ + - + - ]: 152535 : for (int slotno = bankstart; slotno < bankend; slotno++)
643 : : {
644 [ + - ]: 76268 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
645 [ + + + - ]: 76268 : shared->page_number[slotno] == pageno &&
646 : 76267 : shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
647 : : {
648 : : /* See comments for SlruRecentlyUsed() */
649 : 76267 : SlruRecentlyUsed(shared, slotno);
650 : :
651 : : /* update the stats counter of pages found in the SLRU */
652 : 76267 : pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
653 : :
654 : 76267 : return slotno;
655 : : }
656 : 1 : }
657 : :
658 : : /* No luck, so switch to normal exclusive lock and do regular read */
659 : 0 : LWLockRelease(banklock);
660 : 0 : LWLockAcquire(banklock, LW_EXCLUSIVE);
661 : :
662 : 0 : return SimpleLruReadPage(ctl, pageno, true, xid);
663 : 76267 : }
664 : :
665 : : /*
666 : : * Write a page from a shared buffer, if necessary.
667 : : * Does nothing if the specified slot is not dirty.
668 : : *
669 : : * NOTE: only one write attempt is made here. Hence, it is possible that
670 : : * the page is still dirty at exit (if someone else re-dirtied it during
671 : : * the write). However, we *do* attempt a fresh write even if the page
672 : : * is already being written; this is for checkpoints.
673 : : *
674 : : * Bank lock must be held at entry, and will be held at exit.
675 : : */
676 : : static void
677 : 26 : SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata)
678 : : {
679 : 26 : SlruShared shared = ctl->shared;
680 : 26 : int64 pageno = shared->page_number[slotno];
681 : 26 : int bankno = SlotGetBankNumber(slotno);
682 : 26 : bool ok;
683 : :
684 [ + - ]: 26 : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
685 [ + - ]: 26 : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
686 : :
687 : : /* If a write is in progress, wait for it to finish */
688 [ + - - + ]: 26 : while (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
689 : 0 : shared->page_number[slotno] == pageno)
690 : : {
691 : 0 : SimpleLruWaitIO(ctl, slotno);
692 : : }
693 : :
694 : : /*
695 : : * Do nothing if page is not dirty, or if buffer no longer contains the
696 : : * same page we were called for.
697 : : */
698 [ + + ]: 26 : if (!shared->page_dirty[slotno] ||
699 [ + - - + ]: 15 : shared->page_status[slotno] != SLRU_PAGE_VALID ||
700 : 15 : shared->page_number[slotno] != pageno)
701 : 11 : return;
702 : :
703 : : /*
704 : : * Mark the slot write-busy, and clear the dirtybit. After this point, a
705 : : * transaction status update on this page will mark it dirty again.
706 : : */
707 : 15 : shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS;
708 : 15 : shared->page_dirty[slotno] = false;
709 : :
710 : : /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
711 : 15 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
712 : :
713 : : /* Release bank lock while doing I/O */
714 : 15 : LWLockRelease(&shared->bank_locks[bankno].lock);
715 : :
716 : : /* Do the write */
717 : 15 : ok = SlruPhysicalWritePage(ctl, pageno, slotno, fdata);
718 : :
719 : : /* If we failed, and we're in a flush, better close the files */
720 [ - + # # ]: 15 : if (!ok && fdata)
721 : : {
722 [ # # ]: 0 : for (int i = 0; i < fdata->num_files; i++)
723 : 0 : CloseTransientFile(fdata->fd[i]);
724 : 0 : }
725 : :
726 : : /* Re-acquire bank lock and update page state */
727 : 15 : LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
728 : :
729 [ + - ]: 15 : Assert(shared->page_number[slotno] == pageno &&
730 : : shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS);
731 : :
732 : : /* If we failed to write, mark the page dirty again */
733 [ + - ]: 15 : if (!ok)
734 : 0 : shared->page_dirty[slotno] = true;
735 : :
736 : 15 : shared->page_status[slotno] = SLRU_PAGE_VALID;
737 : :
738 : 15 : LWLockRelease(&shared->buffer_locks[slotno].lock);
739 : :
740 : : /* Now it's okay to ereport if we failed */
741 [ + - ]: 15 : if (!ok)
742 : 0 : SlruReportIOError(ctl, pageno, InvalidTransactionId);
743 : :
744 : : /* If part of a checkpoint, count this as a SLRU buffer written. */
745 [ + + ]: 15 : if (fdata)
746 : : {
747 : 11 : CheckpointStats.ckpt_slru_written++;
748 : 11 : PendingCheckpointerStats.slru_written++;
749 : 11 : }
750 [ - + ]: 26 : }
751 : :
752 : : /*
753 : : * Wrapper of SlruInternalWritePage, for external callers.
754 : : * fdata is always passed a NULL here.
755 : : */
756 : : void
757 : 4 : SimpleLruWritePage(SlruCtl ctl, int slotno)
758 : : {
759 [ + - ]: 4 : Assert(ctl->shared->page_status[slotno] != SLRU_PAGE_EMPTY);
760 : :
761 : 4 : SlruInternalWritePage(ctl, slotno, NULL);
762 : 4 : }
763 : :
764 : : /*
765 : : * Return whether the given page exists on disk.
766 : : *
767 : : * A false return means that either the file does not exist, or that it's not
768 : : * large enough to contain the given page.
769 : : */
770 : : bool
771 : 0 : SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int64 pageno)
772 : : {
773 : 0 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
774 : 0 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
775 : 0 : int offset = rpageno * BLCKSZ;
776 : 0 : char path[MAXPGPATH];
777 : 0 : int fd;
778 : 0 : bool result;
779 : 0 : off_t endpos;
780 : :
781 : : /* update the stats counter of checked pages */
782 : 0 : pgstat_count_slru_blocks_exists(ctl->shared->slru_stats_idx);
783 : :
784 : 0 : SlruFileName(ctl, path, segno);
785 : :
786 : 0 : fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
787 [ # # ]: 0 : if (fd < 0)
788 : : {
789 : : /* expected: file doesn't exist */
790 [ # # ]: 0 : if (errno == ENOENT)
791 : 0 : return false;
792 : :
793 : : /* report error normally */
794 : 0 : slru_errcause = SLRU_OPEN_FAILED;
795 : 0 : slru_errno = errno;
796 : 0 : SlruReportIOError(ctl, pageno, 0);
797 : 0 : }
798 : :
799 [ # # ]: 0 : if ((endpos = lseek(fd, 0, SEEK_END)) < 0)
800 : : {
801 : 0 : slru_errcause = SLRU_SEEK_FAILED;
802 : 0 : slru_errno = errno;
803 : 0 : SlruReportIOError(ctl, pageno, 0);
804 : 0 : }
805 : :
806 : 0 : result = endpos >= (off_t) (offset + BLCKSZ);
807 : :
808 [ # # ]: 0 : if (CloseTransientFile(fd) != 0)
809 : : {
810 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
811 : 0 : slru_errno = errno;
812 : 0 : return false;
813 : : }
814 : :
815 : 0 : return result;
816 : 0 : }
817 : :
818 : : /*
819 : : * Physical read of a (previously existing) page into a buffer slot
820 : : *
821 : : * On failure, we cannot just ereport(ERROR) since caller has put state in
822 : : * shared memory that must be undone. So, we return false and save enough
823 : : * info in static variables to let SlruReportIOError make the report.
824 : : *
825 : : * For now, assume it's not worth keeping a file pointer open across
826 : : * read/write operations. We could cache one virtual file pointer ...
827 : : */
828 : : static bool
829 : 4 : SlruPhysicalReadPage(SlruCtl ctl, int64 pageno, int slotno)
830 : : {
831 : 4 : SlruShared shared = ctl->shared;
832 : 4 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
833 : 4 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
834 : 4 : off_t offset = rpageno * BLCKSZ;
835 : 4 : char path[MAXPGPATH];
836 : 4 : int fd;
837 : :
838 : 4 : SlruFileName(ctl, path, segno);
839 : :
840 : : /*
841 : : * In a crash-and-restart situation, it's possible for us to receive
842 : : * commands to set the commit status of transactions whose bits are in
843 : : * already-truncated segments of the commit log (see notes in
844 : : * SlruPhysicalWritePage). Hence, if we are InRecovery, allow the case
845 : : * where the file doesn't exist, and return zeroes instead.
846 : : */
847 : 4 : fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
848 [ + - ]: 4 : if (fd < 0)
849 : : {
850 [ # # # # ]: 0 : if (errno != ENOENT || !InRecovery)
851 : : {
852 : 0 : slru_errcause = SLRU_OPEN_FAILED;
853 : 0 : slru_errno = errno;
854 : 0 : return false;
855 : : }
856 : :
857 [ # # # # ]: 0 : ereport(LOG,
858 : : (errmsg("file \"%s\" doesn't exist, reading as zeroes",
859 : : path)));
860 [ # # # # : 0 : MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
# # # # #
# ]
861 : 0 : return true;
862 : : }
863 : :
864 : 4 : errno = 0;
865 : 4 : pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
866 [ - + ]: 4 : if (pg_pread(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
867 : : {
868 : 0 : pgstat_report_wait_end();
869 : 0 : slru_errcause = SLRU_READ_FAILED;
870 : 0 : slru_errno = errno;
871 : 0 : CloseTransientFile(fd);
872 : 0 : return false;
873 : : }
874 : 4 : pgstat_report_wait_end();
875 : :
876 [ - + ]: 4 : if (CloseTransientFile(fd) != 0)
877 : : {
878 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
879 : 0 : slru_errno = errno;
880 : 0 : return false;
881 : : }
882 : :
883 : 4 : return true;
884 : 4 : }
885 : :
886 : : /*
887 : : * Physical write of a page from a buffer slot
888 : : *
889 : : * On failure, we cannot just ereport(ERROR) since caller has put state in
890 : : * shared memory that must be undone. So, we return false and save enough
891 : : * info in static variables to let SlruReportIOError make the report.
892 : : *
893 : : * For now, assume it's not worth keeping a file pointer open across
894 : : * independent read/write operations. We do batch operations during
895 : : * SimpleLruWriteAll, though.
896 : : *
897 : : * fdata is NULL for a standalone write, pointer to open-file info during
898 : : * SimpleLruWriteAll.
899 : : */
900 : : static bool
901 : 15 : SlruPhysicalWritePage(SlruCtl ctl, int64 pageno, int slotno, SlruWriteAll fdata)
902 : : {
903 : 15 : SlruShared shared = ctl->shared;
904 : 15 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
905 : 15 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
906 : 15 : off_t offset = rpageno * BLCKSZ;
907 : 15 : char path[MAXPGPATH];
908 : 15 : int fd = -1;
909 : :
910 : : /* update the stats counter of written pages */
911 : 15 : pgstat_count_slru_blocks_written(shared->slru_stats_idx);
912 : :
913 : : /*
914 : : * Honor the write-WAL-before-data rule, if appropriate, so that we do not
915 : : * write out data before associated WAL records. This is the same action
916 : : * performed during FlushBuffer() in the main buffer manager.
917 : : */
918 [ + + ]: 15 : if (shared->group_lsn != NULL)
919 : : {
920 : : /*
921 : : * We must determine the largest async-commit LSN for the page. This
922 : : * is a bit tedious, but since this entire function is a slow path
923 : : * anyway, it seems better to do this here than to maintain a per-page
924 : : * LSN variable (which'd need an extra comparison in the
925 : : * transaction-commit path).
926 : : */
927 : 6 : XLogRecPtr max_lsn;
928 : 6 : int lsnindex;
929 : :
930 : 6 : lsnindex = slotno * shared->lsn_groups_per_page;
931 : 6 : max_lsn = shared->group_lsn[lsnindex++];
932 [ + + ]: 6144 : for (int lsnoff = 1; lsnoff < shared->lsn_groups_per_page; lsnoff++)
933 : : {
934 : 6138 : XLogRecPtr this_lsn = shared->group_lsn[lsnindex++];
935 : :
936 [ + - ]: 6138 : if (max_lsn < this_lsn)
937 : 0 : max_lsn = this_lsn;
938 : 6138 : }
939 : :
940 [ + - ]: 6 : if (XLogRecPtrIsValid(max_lsn))
941 : : {
942 : : /*
943 : : * As noted above, elog(ERROR) is not acceptable here, so if
944 : : * XLogFlush were to fail, we must PANIC. This isn't much of a
945 : : * restriction because XLogFlush is just about all critical
946 : : * section anyway, but let's make sure.
947 : : */
948 : 0 : START_CRIT_SECTION();
949 : 0 : XLogFlush(max_lsn);
950 [ # # ]: 0 : END_CRIT_SECTION();
951 : 0 : }
952 : 6 : }
953 : :
954 : : /*
955 : : * During a SimpleLruWriteAll, we may already have the desired file open.
956 : : */
957 [ + + ]: 15 : if (fdata)
958 : : {
959 [ - + ]: 11 : for (int i = 0; i < fdata->num_files; i++)
960 : : {
961 [ # # ]: 0 : if (fdata->segno[i] == segno)
962 : : {
963 : 0 : fd = fdata->fd[i];
964 : 0 : break;
965 : : }
966 : 0 : }
967 : 11 : }
968 : :
969 [ - + ]: 15 : if (fd < 0)
970 : : {
971 : : /*
972 : : * If the file doesn't already exist, we should create it. It is
973 : : * possible for this to need to happen when writing a page that's not
974 : : * first in its segment; we assume the OS can cope with that. (Note:
975 : : * it might seem that it'd be okay to create files only when
976 : : * SimpleLruZeroPage is called for the first page of a segment.
977 : : * However, if after a crash and restart the REDO logic elects to
978 : : * replay the log from a checkpoint before the latest one, then it's
979 : : * possible that we will get commands to set transaction status of
980 : : * transactions that have already been truncated from the commit log.
981 : : * Easiest way to deal with that is to accept references to
982 : : * nonexistent files here and in SlruPhysicalReadPage.)
983 : : *
984 : : * Note: it is possible for more than one backend to be executing this
985 : : * code simultaneously for different pages of the same file. Hence,
986 : : * don't use O_EXCL or O_TRUNC or anything like that.
987 : : */
988 : 15 : SlruFileName(ctl, path, segno);
989 : 15 : fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY);
990 [ + - ]: 15 : if (fd < 0)
991 : : {
992 : 0 : slru_errcause = SLRU_OPEN_FAILED;
993 : 0 : slru_errno = errno;
994 : 0 : return false;
995 : : }
996 : :
997 [ + + ]: 15 : if (fdata)
998 : : {
999 [ + - ]: 11 : if (fdata->num_files < MAX_WRITEALL_BUFFERS)
1000 : : {
1001 : 11 : fdata->fd[fdata->num_files] = fd;
1002 : 11 : fdata->segno[fdata->num_files] = segno;
1003 : 11 : fdata->num_files++;
1004 : 11 : }
1005 : : else
1006 : : {
1007 : : /*
1008 : : * In the unlikely event that we exceed MAX_WRITEALL_BUFFERS,
1009 : : * fall back to treating it as a standalone write.
1010 : : */
1011 : 0 : fdata = NULL;
1012 : : }
1013 : 11 : }
1014 : 15 : }
1015 : :
1016 : 15 : errno = 0;
1017 : 15 : pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE);
1018 [ - + ]: 15 : if (pg_pwrite(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
1019 : : {
1020 : 0 : pgstat_report_wait_end();
1021 : : /* if write didn't set errno, assume problem is no disk space */
1022 [ # # ]: 0 : if (errno == 0)
1023 : 0 : errno = ENOSPC;
1024 : 0 : slru_errcause = SLRU_WRITE_FAILED;
1025 : 0 : slru_errno = errno;
1026 [ # # ]: 0 : if (!fdata)
1027 : 0 : CloseTransientFile(fd);
1028 : 0 : return false;
1029 : : }
1030 : 15 : pgstat_report_wait_end();
1031 : :
1032 : : /* Queue up a sync request for the checkpointer. */
1033 [ + + ]: 15 : if (ctl->sync_handler != SYNC_HANDLER_NONE)
1034 : : {
1035 : 11 : FileTag tag;
1036 : :
1037 : 11 : INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
1038 [ + - ]: 11 : if (!RegisterSyncRequest(&tag, SYNC_REQUEST, false))
1039 : : {
1040 : : /* No space to enqueue sync request. Do it synchronously. */
1041 : 0 : pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC);
1042 [ # # ]: 0 : if (pg_fsync(fd) != 0)
1043 : : {
1044 : 0 : pgstat_report_wait_end();
1045 : 0 : slru_errcause = SLRU_FSYNC_FAILED;
1046 : 0 : slru_errno = errno;
1047 : 0 : CloseTransientFile(fd);
1048 : 0 : return false;
1049 : : }
1050 : 0 : pgstat_report_wait_end();
1051 : 0 : }
1052 [ - + ]: 11 : }
1053 : :
1054 : : /* Close file, unless part of flush request. */
1055 [ + + ]: 15 : if (!fdata)
1056 : : {
1057 [ - + ]: 4 : if (CloseTransientFile(fd) != 0)
1058 : : {
1059 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
1060 : 0 : slru_errno = errno;
1061 : 0 : return false;
1062 : : }
1063 : 4 : }
1064 : :
1065 : 15 : return true;
1066 : 15 : }
1067 : :
1068 : : /*
1069 : : * Issue the error message after failure of SlruPhysicalReadPage or
1070 : : * SlruPhysicalWritePage. Call this after cleaning up shared-memory state.
1071 : : */
1072 : : static void
1073 : 0 : SlruReportIOError(SlruCtl ctl, int64 pageno, TransactionId xid)
1074 : : {
1075 : 0 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
1076 : 0 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
1077 : 0 : int offset = rpageno * BLCKSZ;
1078 : 0 : char path[MAXPGPATH];
1079 : :
1080 : 0 : SlruFileName(ctl, path, segno);
1081 : 0 : errno = slru_errno;
1082 [ # # # # : 0 : switch (slru_errcause)
# # # ]
1083 : : {
1084 : : case SLRU_OPEN_FAILED:
1085 [ # # # # ]: 0 : ereport(ERROR,
1086 : : (errcode_for_file_access(),
1087 : : errmsg("could not access status of transaction %u", xid),
1088 : : errdetail("Could not open file \"%s\": %m.", path)));
1089 : 0 : break;
1090 : : case SLRU_SEEK_FAILED:
1091 [ # # # # ]: 0 : ereport(ERROR,
1092 : : (errcode_for_file_access(),
1093 : : errmsg("could not access status of transaction %u", xid),
1094 : : errdetail("Could not seek in file \"%s\" to offset %d: %m.",
1095 : : path, offset)));
1096 : 0 : break;
1097 : : case SLRU_READ_FAILED:
1098 [ # # ]: 0 : if (errno)
1099 [ # # # # ]: 0 : ereport(ERROR,
1100 : : (errcode_for_file_access(),
1101 : : errmsg("could not access status of transaction %u", xid),
1102 : : errdetail("Could not read from file \"%s\" at offset %d: %m.",
1103 : : path, offset)));
1104 : : else
1105 [ # # # # ]: 0 : ereport(ERROR,
1106 : : (errmsg("could not access status of transaction %u", xid),
1107 : : errdetail("Could not read from file \"%s\" at offset %d: read too few bytes.", path, offset)));
1108 : 0 : break;
1109 : : case SLRU_WRITE_FAILED:
1110 [ # # ]: 0 : if (errno)
1111 [ # # # # ]: 0 : ereport(ERROR,
1112 : : (errcode_for_file_access(),
1113 : : errmsg("could not access status of transaction %u", xid),
1114 : : errdetail("Could not write to file \"%s\" at offset %d: %m.",
1115 : : path, offset)));
1116 : : else
1117 [ # # # # ]: 0 : ereport(ERROR,
1118 : : (errmsg("could not access status of transaction %u", xid),
1119 : : errdetail("Could not write to file \"%s\" at offset %d: wrote too few bytes.",
1120 : : path, offset)));
1121 : 0 : break;
1122 : : case SLRU_FSYNC_FAILED:
1123 [ # # # # : 0 : ereport(data_sync_elevel(ERROR),
# # ]
1124 : : (errcode_for_file_access(),
1125 : : errmsg("could not access status of transaction %u", xid),
1126 : : errdetail("Could not fsync file \"%s\": %m.",
1127 : : path)));
1128 : 0 : break;
1129 : : case SLRU_CLOSE_FAILED:
1130 [ # # # # ]: 0 : ereport(ERROR,
1131 : : (errcode_for_file_access(),
1132 : : errmsg("could not access status of transaction %u", xid),
1133 : : errdetail("Could not close file \"%s\": %m.",
1134 : : path)));
1135 : 0 : break;
1136 : : default:
1137 : : /* can't get here, we trust */
1138 [ # # # # ]: 0 : elog(ERROR, "unrecognized SimpleLru error cause: %d",
1139 : : (int) slru_errcause);
1140 : 0 : break;
1141 : : }
1142 : 0 : }
1143 : :
1144 : : /*
1145 : : * Mark a buffer slot "most recently used".
1146 : : */
1147 : : static inline void
1148 : 98480 : SlruRecentlyUsed(SlruShared shared, int slotno)
1149 : : {
1150 : 98480 : int bankno = SlotGetBankNumber(slotno);
1151 : 98480 : int new_lru_count = shared->bank_cur_lru_count[bankno];
1152 : :
1153 [ + - ]: 98480 : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
1154 : :
1155 : : /*
1156 : : * The reason for the if-test is that there are often many consecutive
1157 : : * accesses to the same page (particularly the latest page). By
1158 : : * suppressing useless increments of bank_cur_lru_count, we reduce the
1159 : : * probability that old pages' counts will "wrap around" and make them
1160 : : * appear recently used.
1161 : : *
1162 : : * We allow this code to be executed concurrently by multiple processes
1163 : : * within SimpleLruReadPage_ReadOnly(). As long as int reads and writes
1164 : : * are atomic, this should not cause any completely-bogus values to enter
1165 : : * the computation. However, it is possible for either bank_cur_lru_count
1166 : : * or individual page_lru_count entries to be "reset" to lower values than
1167 : : * they should have, in case a process is delayed while it executes this
1168 : : * function. With care in SlruSelectLRUPage(), this does little harm, and
1169 : : * in any case the absolute worst possible consequence is a nonoptimal
1170 : : * choice of page to evict. The gain from allowing concurrent reads of
1171 : : * SLRU pages seems worth it.
1172 : : */
1173 [ + + ]: 98480 : if (new_lru_count != shared->page_lru_count[slotno])
1174 : : {
1175 : 25 : shared->bank_cur_lru_count[bankno] = ++new_lru_count;
1176 : 25 : shared->page_lru_count[slotno] = new_lru_count;
1177 : 25 : }
1178 : 98480 : }
1179 : :
1180 : : /*
1181 : : * Select the slot to re-use when we need a free slot for the given page.
1182 : : *
1183 : : * The target page number is passed not only because we need to know the
1184 : : * correct bank to use, but also because we need to consider the possibility
1185 : : * that some other process reads in the target page while we are doing I/O to
1186 : : * free a slot. Hence, check or recheck to see if any slot already holds the
1187 : : * target page, and return that slot if so. Thus, the returned slot is
1188 : : * *either* a slot already holding the pageno (could be any state except
1189 : : * EMPTY), *or* a freeable slot (state EMPTY or CLEAN).
1190 : : *
1191 : : * The correct bank lock must be held at entry, and will be held at exit.
1192 : : */
1193 : : static int
1194 : 22213 : SlruSelectLRUPage(SlruCtl ctl, int64 pageno)
1195 : : {
1196 : 22213 : SlruShared shared = ctl->shared;
1197 : :
1198 : : /* Outer loop handles restart after I/O */
1199 : 22213 : for (;;)
1200 : : {
1201 : 22213 : int cur_count;
1202 : 22213 : int bestvalidslot = 0; /* keep compiler quiet */
1203 : 22213 : int best_valid_delta = -1;
1204 : 22213 : int64 best_valid_page_number = 0; /* keep compiler quiet */
1205 : 22213 : int bestinvalidslot = 0; /* keep compiler quiet */
1206 : 22213 : int best_invalid_delta = -1;
1207 : 22213 : int64 best_invalid_page_number = 0; /* keep compiler quiet */
1208 : 22213 : int bankno = pageno % ctl->nbanks;
1209 : 22213 : int bankstart = bankno * SLRU_BANK_SIZE;
1210 : 22213 : int bankend = bankstart + SLRU_BANK_SIZE;
1211 : :
1212 [ + - ]: 22213 : Assert(LWLockHeldByMe(SimpleLruGetBankLock(ctl, pageno)));
1213 : :
1214 : : /* See if page already has a buffer assigned */
1215 [ + + + + ]: 44922 : for (int slotno = bankstart; slotno < bankend; slotno++)
1216 : : {
1217 [ + + + + ]: 22709 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
1218 : 22322 : shared->page_number[slotno] == pageno)
1219 : 22188 : return slotno;
1220 : 521 : }
1221 : :
1222 : : /*
1223 : : * If we find any EMPTY slot, just select that one. Else choose a
1224 : : * victim page to replace. We normally take the least recently used
1225 : : * valid page, but we will never take the slot containing
1226 : : * latest_page_number, even if it appears least recently used. We
1227 : : * will select a slot that is already I/O busy only if there is no
1228 : : * other choice: a read-busy slot will not be least recently used once
1229 : : * the read finishes, and waiting for an I/O on a write-busy slot is
1230 : : * inferior to just picking some other slot. Testing shows the slot
1231 : : * we pick instead will often be clean, allowing us to begin a read at
1232 : : * once.
1233 : : *
1234 : : * Normally the page_lru_count values will all be different and so
1235 : : * there will be a well-defined LRU page. But since we allow
1236 : : * concurrent execution of SlruRecentlyUsed() within
1237 : : * SimpleLruReadPage_ReadOnly(), it is possible that multiple pages
1238 : : * acquire the same lru_count values. In that case we break ties by
1239 : : * choosing the furthest-back page.
1240 : : *
1241 : : * Notice that this next line forcibly advances cur_lru_count to a
1242 : : * value that is certainly beyond any value that will be in the
1243 : : * page_lru_count array after the loop finishes. This ensures that
1244 : : * the next execution of SlruRecentlyUsed will mark the page newly
1245 : : * used, even if it's for a page that has the current counter value.
1246 : : * That gets us back on the path to having good data when there are
1247 : : * multiple pages with the same lru_count.
1248 : : */
1249 : 25 : cur_count = (shared->bank_cur_lru_count[bankno])++;
1250 [ - + + - ]: 62 : for (int slotno = bankstart; slotno < bankend; slotno++)
1251 : : {
1252 : 37 : int this_delta;
1253 : 37 : int64 this_page_number;
1254 : :
1255 [ + + ]: 37 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1256 : 25 : return slotno;
1257 : :
1258 : 12 : this_delta = cur_count - shared->page_lru_count[slotno];
1259 [ + - ]: 12 : if (this_delta < 0)
1260 : : {
1261 : : /*
1262 : : * Clean up in case shared updates have caused cur_count
1263 : : * increments to get "lost". We back off the page counts,
1264 : : * rather than trying to increase cur_count, to avoid any
1265 : : * question of infinite loops or failure in the presence of
1266 : : * wrapped-around counts.
1267 : : */
1268 : 0 : shared->page_lru_count[slotno] = cur_count;
1269 : 0 : this_delta = 0;
1270 : 0 : }
1271 : :
1272 : : /*
1273 : : * If this page is the one most recently zeroed, don't consider it
1274 : : * an eviction candidate. See comments in SimpleLruZeroPage for an
1275 : : * explanation about the lack of a memory barrier here.
1276 : : */
1277 : 12 : this_page_number = shared->page_number[slotno];
1278 [ - + - + ]: 24 : if (this_page_number ==
1279 : 12 : pg_atomic_read_u64(&shared->latest_page_number))
1280 : 0 : continue;
1281 : :
1282 [ + - ]: 12 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1283 : : {
1284 [ + + # # ]: 12 : if (this_delta > best_valid_delta ||
1285 [ - + ]: 4 : (this_delta == best_valid_delta &&
1286 : 0 : ctl->PagePrecedes(this_page_number,
1287 : 0 : best_valid_page_number)))
1288 : : {
1289 : 8 : bestvalidslot = slotno;
1290 : 8 : best_valid_delta = this_delta;
1291 : 8 : best_valid_page_number = this_page_number;
1292 : 8 : }
1293 : 12 : }
1294 : : else
1295 : : {
1296 [ # # # # ]: 0 : if (this_delta > best_invalid_delta ||
1297 [ # # ]: 0 : (this_delta == best_invalid_delta &&
1298 : 0 : ctl->PagePrecedes(this_page_number,
1299 : 0 : best_invalid_page_number)))
1300 : : {
1301 : 0 : bestinvalidslot = slotno;
1302 : 0 : best_invalid_delta = this_delta;
1303 : 0 : best_invalid_page_number = this_page_number;
1304 : 0 : }
1305 : : }
1306 [ - + + ]: 37 : }
1307 : :
1308 : : /*
1309 : : * If all pages (except possibly the latest one) are I/O busy, we'll
1310 : : * have to wait for an I/O to complete and then retry. In that
1311 : : * unhappy case, we choose to wait for the I/O on the least recently
1312 : : * used slot, on the assumption that it was likely initiated first of
1313 : : * all the I/Os in progress and may therefore finish first.
1314 : : */
1315 [ # # ]: 0 : if (best_valid_delta < 0)
1316 : : {
1317 : 0 : SimpleLruWaitIO(ctl, bestinvalidslot);
1318 : 0 : continue;
1319 : : }
1320 : :
1321 : : /*
1322 : : * If the selected page is clean, we're set.
1323 : : */
1324 [ # # ]: 0 : if (!shared->page_dirty[bestvalidslot])
1325 : 0 : return bestvalidslot;
1326 : :
1327 : : /*
1328 : : * Write the page.
1329 : : */
1330 : 0 : SlruInternalWritePage(ctl, bestvalidslot, NULL);
1331 : :
1332 : : /*
1333 : : * Now loop back and try again. This is the easiest way of dealing
1334 : : * with corner cases such as the victim page being re-dirtied while we
1335 : : * wrote it.
1336 : : */
1337 [ - - + ]: 22213 : }
1338 : 22213 : }
1339 : :
1340 : : /*
1341 : : * Write dirty pages to disk during checkpoint or database shutdown. Flushing
1342 : : * is deferred until the next call to ProcessSyncRequests(), though we do fsync
1343 : : * the containing directory here to make sure that newly created directory
1344 : : * entries are on disk.
1345 : : */
1346 : : void
1347 : 35 : SimpleLruWriteAll(SlruCtl ctl, bool allow_redirtied)
1348 : : {
1349 : 35 : SlruShared shared = ctl->shared;
1350 : 35 : SlruWriteAllData fdata;
1351 : 35 : int64 pageno = 0;
1352 : 35 : int prevbank = SlotGetBankNumber(0);
1353 : 35 : bool ok;
1354 : :
1355 : : /* update the stats counter of flushes */
1356 : 35 : pgstat_count_slru_flush(shared->slru_stats_idx);
1357 : :
1358 : : /*
1359 : : * Find and write dirty pages
1360 : : */
1361 : 35 : fdata.num_files = 0;
1362 : :
1363 : 35 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1364 : :
1365 [ + + ]: 1043 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1366 : : {
1367 : 1008 : int curbank = SlotGetBankNumber(slotno);
1368 : :
1369 : : /*
1370 : : * If the current bank lock is not same as the previous bank lock then
1371 : : * release the previous lock and acquire the new lock.
1372 : : */
1373 [ + + ]: 1008 : if (curbank != prevbank)
1374 : : {
1375 : 28 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1376 : 28 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1377 : 28 : prevbank = curbank;
1378 : 28 : }
1379 : :
1380 : : /* Do nothing if slot is unused */
1381 [ + + ]: 1008 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1382 : 986 : continue;
1383 : :
1384 : 22 : SlruInternalWritePage(ctl, slotno, &fdata);
1385 : :
1386 : : /*
1387 : : * In some places (e.g. checkpoints), we cannot assert that the slot
1388 : : * is clean now, since another process might have re-dirtied it
1389 : : * already. That's okay.
1390 : : */
1391 [ - + # # : 22 : Assert(allow_redirtied ||
# # ]
1392 : : shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
1393 : : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1394 : : !shared->page_dirty[slotno]));
1395 [ - + + ]: 1008 : }
1396 : :
1397 : 35 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1398 : :
1399 : : /*
1400 : : * Now close any files that were open
1401 : : */
1402 : 35 : ok = true;
1403 [ + + ]: 46 : for (int i = 0; i < fdata.num_files; i++)
1404 : : {
1405 [ + - ]: 11 : if (CloseTransientFile(fdata.fd[i]) != 0)
1406 : : {
1407 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
1408 : 0 : slru_errno = errno;
1409 : 0 : pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT;
1410 : 0 : ok = false;
1411 : 0 : }
1412 : 11 : }
1413 [ + - ]: 35 : if (!ok)
1414 : 0 : SlruReportIOError(ctl, pageno, InvalidTransactionId);
1415 : :
1416 : : /* Ensure that directory entries for new files are on disk. */
1417 [ + + ]: 35 : if (ctl->sync_handler != SYNC_HANDLER_NONE)
1418 : 28 : fsync_fname(ctl->Dir, true);
1419 : 35 : }
1420 : :
1421 : : /*
1422 : : * Remove all segments before the one holding the passed page number
1423 : : *
1424 : : * All SLRUs prevent concurrent calls to this function, either with an LWLock
1425 : : * or by calling it only as part of a checkpoint. Mutual exclusion must begin
1426 : : * before computing cutoffPage. Mutual exclusion must end after any limit
1427 : : * update that would permit other backends to write fresh data into the
1428 : : * segment immediately preceding the one containing cutoffPage. Otherwise,
1429 : : * when the SLRU is quite full, SimpleLruTruncate() might delete that segment
1430 : : * after it has accrued freshly-written data.
1431 : : */
1432 : : void
1433 : 7 : SimpleLruTruncate(SlruCtl ctl, int64 cutoffPage)
1434 : : {
1435 : 7 : SlruShared shared = ctl->shared;
1436 : 7 : int prevbank;
1437 : :
1438 : : /* update the stats counter of truncates */
1439 : 7 : pgstat_count_slru_truncate(shared->slru_stats_idx);
1440 : :
1441 : : /*
1442 : : * Scan shared memory and remove any pages preceding the cutoff page, to
1443 : : * ensure we won't rewrite them later. (Since this is normally called in
1444 : : * or just after a checkpoint, any dirty pages should have been flushed
1445 : : * already ... we're just being extra careful here.)
1446 : : */
1447 : : restart:
1448 : :
1449 : : /*
1450 : : * An important safety check: the current endpoint page must not be
1451 : : * eligible for removal. This check is just a backstop against wraparound
1452 : : * bugs elsewhere in SLRU handling, so we don't care if we read a slightly
1453 : : * outdated value; therefore we don't add a memory barrier.
1454 : : */
1455 [ + - + - ]: 14 : if (ctl->PagePrecedes(pg_atomic_read_u64(&shared->latest_page_number),
1456 : 7 : cutoffPage))
1457 : : {
1458 [ # # # # ]: 0 : ereport(LOG,
1459 : : (errmsg("could not truncate directory \"%s\": apparent wraparound",
1460 : : ctl->Dir)));
1461 : 0 : return;
1462 : : }
1463 : :
1464 : 7 : prevbank = SlotGetBankNumber(0);
1465 : 7 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1466 [ + + - + ]: 231 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1467 : : {
1468 : 224 : int curbank = SlotGetBankNumber(slotno);
1469 : :
1470 : : /*
1471 : : * If the current bank lock is not same as the previous bank lock then
1472 : : * release the previous lock and acquire the new lock.
1473 : : */
1474 [ + + ]: 224 : if (curbank != prevbank)
1475 : : {
1476 : 7 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1477 : 7 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1478 : 7 : prevbank = curbank;
1479 : 7 : }
1480 : :
1481 [ + + ]: 224 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1482 : 217 : continue;
1483 [ - + ]: 7 : if (!ctl->PagePrecedes(shared->page_number[slotno], cutoffPage))
1484 : 7 : continue;
1485 : :
1486 : : /*
1487 : : * If page is clean, just change state to EMPTY (expected case).
1488 : : */
1489 [ # # # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1490 : 0 : !shared->page_dirty[slotno])
1491 : : {
1492 : 0 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
1493 : 0 : continue;
1494 : : }
1495 : :
1496 : : /*
1497 : : * Hmm, we have (or may have) I/O operations acting on the page, so
1498 : : * we've got to wait for them to finish and then start again. This is
1499 : : * the same logic as in SlruSelectLRUPage. (XXX if page is dirty,
1500 : : * wouldn't it be OK to just discard it without writing it?
1501 : : * SlruMayDeleteSegment() uses a stricter qualification, so we might
1502 : : * not delete this page in the end; even if we don't delete it, we
1503 : : * won't have cause to read its data again. For now, keep the logic
1504 : : * the same as it was.)
1505 : : */
1506 [ # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1507 : 0 : SlruInternalWritePage(ctl, slotno, NULL);
1508 : : else
1509 : 0 : SimpleLruWaitIO(ctl, slotno);
1510 : :
1511 : 0 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1512 : 0 : goto restart;
1513 [ - + ]: 224 : }
1514 : :
1515 : 7 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1516 : :
1517 : : /* Now we can remove the old segment(s) */
1518 : 7 : (void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage);
1519 : 7 : }
1520 : :
1521 : : /*
1522 : : * Delete an individual SLRU segment.
1523 : : *
1524 : : * NB: This does not touch the SLRU buffers themselves, callers have to ensure
1525 : : * they either can't yet contain anything, or have already been cleaned out.
1526 : : */
1527 : : static void
1528 : 0 : SlruInternalDeleteSegment(SlruCtl ctl, int64 segno)
1529 : : {
1530 : 0 : char path[MAXPGPATH];
1531 : :
1532 : : /* Forget any fsync requests queued for this segment. */
1533 [ # # ]: 0 : if (ctl->sync_handler != SYNC_HANDLER_NONE)
1534 : : {
1535 : 0 : FileTag tag;
1536 : :
1537 : 0 : INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
1538 : 0 : RegisterSyncRequest(&tag, SYNC_FORGET_REQUEST, true);
1539 : 0 : }
1540 : :
1541 : : /* Unlink the file. */
1542 : 0 : SlruFileName(ctl, path, segno);
1543 [ # # # # ]: 0 : ereport(DEBUG2, (errmsg_internal("removing file \"%s\"", path)));
1544 : 0 : unlink(path);
1545 : 0 : }
1546 : :
1547 : : /*
1548 : : * Delete an individual SLRU segment, identified by the segment number.
1549 : : */
1550 : : void
1551 : 0 : SlruDeleteSegment(SlruCtl ctl, int64 segno)
1552 : : {
1553 : 0 : SlruShared shared = ctl->shared;
1554 : 0 : int prevbank = SlotGetBankNumber(0);
1555 : 0 : bool did_write;
1556 : :
1557 : : /* Clean out any possibly existing references to the segment. */
1558 : 0 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1559 : : restart:
1560 : 0 : did_write = false;
1561 [ # # ]: 0 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1562 : : {
1563 : 0 : int64 pagesegno;
1564 : 0 : int curbank = SlotGetBankNumber(slotno);
1565 : :
1566 : : /*
1567 : : * If the current bank lock is not same as the previous bank lock then
1568 : : * release the previous lock and acquire the new lock.
1569 : : */
1570 [ # # ]: 0 : if (curbank != prevbank)
1571 : : {
1572 : 0 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1573 : 0 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1574 : 0 : prevbank = curbank;
1575 : 0 : }
1576 : :
1577 [ # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1578 : 0 : continue;
1579 : :
1580 : 0 : pagesegno = shared->page_number[slotno] / SLRU_PAGES_PER_SEGMENT;
1581 : : /* not the segment we're looking for */
1582 [ # # ]: 0 : if (pagesegno != segno)
1583 : 0 : continue;
1584 : :
1585 : : /* If page is clean, just change state to EMPTY (expected case). */
1586 [ # # # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1587 : 0 : !shared->page_dirty[slotno])
1588 : : {
1589 : 0 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
1590 : 0 : continue;
1591 : : }
1592 : :
1593 : : /* Same logic as SimpleLruTruncate() */
1594 [ # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1595 : 0 : SlruInternalWritePage(ctl, slotno, NULL);
1596 : : else
1597 : 0 : SimpleLruWaitIO(ctl, slotno);
1598 : :
1599 : 0 : did_write = true;
1600 [ # # # ]: 0 : }
1601 : :
1602 : : /*
1603 : : * Be extra careful and re-check. The IO functions release the control
1604 : : * lock, so new pages could have been read in.
1605 : : */
1606 [ # # ]: 0 : if (did_write)
1607 : 0 : goto restart;
1608 : :
1609 : 0 : SlruInternalDeleteSegment(ctl, segno);
1610 : :
1611 : 0 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1612 : 0 : }
1613 : :
1614 : : /*
1615 : : * Determine whether a segment is okay to delete.
1616 : : *
1617 : : * segpage is the first page of the segment, and cutoffPage is the oldest (in
1618 : : * PagePrecedes order) page in the SLRU containing still-useful data. Since
1619 : : * every core PagePrecedes callback implements "wrap around", check the
1620 : : * segment's first and last pages:
1621 : : *
1622 : : * first<cutoff && last<cutoff: yes
1623 : : * first<cutoff && last>=cutoff: no; cutoff falls inside this segment
1624 : : * first>=cutoff && last<cutoff: no; wrap point falls inside this segment
1625 : : * first>=cutoff && last>=cutoff: no; every page of this segment is too young
1626 : : */
1627 : : static bool
1628 : 189 : SlruMayDeleteSegment(SlruCtl ctl, int64 segpage, int64 cutoffPage)
1629 : : {
1630 : 189 : int64 seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
1631 : :
1632 [ + - ]: 189 : Assert(segpage % SLRU_PAGES_PER_SEGMENT == 0);
1633 : :
1634 [ + - ]: 189 : return (ctl->PagePrecedes(segpage, cutoffPage) &&
1635 : 0 : ctl->PagePrecedes(seg_last_page, cutoffPage));
1636 : 189 : }
1637 : :
1638 : : #ifdef USE_ASSERT_CHECKING
1639 : : static void
1640 : 90 : SlruPagePrecedesTestOffset(SlruCtl ctl, int per_page, uint32 offset)
1641 : : {
1642 : 90 : TransactionId lhs,
1643 : : rhs;
1644 : 90 : int64 newestPage,
1645 : : oldestPage;
1646 : 90 : TransactionId newestXact,
1647 : : oldestXact;
1648 : :
1649 : : /*
1650 : : * Compare an XID pair having undefined order (see RFC 1982), a pair at
1651 : : * "opposite ends" of the XID space. TransactionIdPrecedes() treats each
1652 : : * as preceding the other. If RHS is oldestXact, LHS is the first XID we
1653 : : * must not assign.
1654 : : */
1655 : 90 : lhs = per_page + offset; /* skip first page to avoid non-normal XIDs */
1656 : 90 : rhs = lhs + (1U << 31);
1657 [ + - ]: 90 : Assert(TransactionIdPrecedes(lhs, rhs));
1658 [ + - ]: 90 : Assert(TransactionIdPrecedes(rhs, lhs));
1659 [ + - ]: 90 : Assert(!TransactionIdPrecedes(lhs - 1, rhs));
1660 [ + - ]: 90 : Assert(TransactionIdPrecedes(rhs, lhs - 1));
1661 [ + - ]: 90 : Assert(TransactionIdPrecedes(lhs + 1, rhs));
1662 [ + - ]: 90 : Assert(!TransactionIdPrecedes(rhs, lhs + 1));
1663 [ + - ]: 90 : Assert(!TransactionIdFollowsOrEquals(lhs, rhs));
1664 [ + - ]: 90 : Assert(!TransactionIdFollowsOrEquals(rhs, lhs));
1665 [ + - ]: 90 : Assert(!ctl->PagePrecedes(lhs / per_page, lhs / per_page));
1666 [ + - ]: 90 : Assert(!ctl->PagePrecedes(lhs / per_page, rhs / per_page));
1667 [ + - ]: 90 : Assert(!ctl->PagePrecedes(rhs / per_page, lhs / per_page));
1668 [ + - ]: 90 : Assert(!ctl->PagePrecedes((lhs - per_page) / per_page, rhs / per_page));
1669 [ + - ]: 90 : Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 3 * per_page) / per_page));
1670 [ + - ]: 90 : Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 2 * per_page) / per_page));
1671 [ + + + - ]: 90 : Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 1 * per_page) / per_page)
1672 : : || (1U << 31) % per_page != 0); /* See CommitTsPagePrecedes() */
1673 [ + + + - ]: 90 : Assert(ctl->PagePrecedes((lhs + 1 * per_page) / per_page, rhs / per_page)
1674 : : || (1U << 31) % per_page != 0);
1675 [ + - ]: 90 : Assert(ctl->PagePrecedes((lhs + 2 * per_page) / per_page, rhs / per_page));
1676 [ + - ]: 90 : Assert(ctl->PagePrecedes((lhs + 3 * per_page) / per_page, rhs / per_page));
1677 [ + - ]: 90 : Assert(!ctl->PagePrecedes(rhs / per_page, (lhs + per_page) / per_page));
1678 : :
1679 : : /*
1680 : : * GetNewTransactionId() has assigned the last XID it can safely use, and
1681 : : * that XID is in the *LAST* page of the second segment. We must not
1682 : : * delete that segment.
1683 : : */
1684 : 90 : newestPage = 2 * SLRU_PAGES_PER_SEGMENT - 1;
1685 : 90 : newestXact = newestPage * per_page + offset;
1686 [ + - ]: 90 : Assert(newestXact / per_page == newestPage);
1687 : 90 : oldestXact = newestXact + 1;
1688 : 90 : oldestXact -= 1U << 31;
1689 : 90 : oldestPage = oldestXact / per_page;
1690 [ + - ]: 90 : Assert(!SlruMayDeleteSegment(ctl,
1691 : : (newestPage -
1692 : : newestPage % SLRU_PAGES_PER_SEGMENT),
1693 : : oldestPage));
1694 : :
1695 : : /*
1696 : : * GetNewTransactionId() has assigned the last XID it can safely use, and
1697 : : * that XID is in the *FIRST* page of the second segment. We must not
1698 : : * delete that segment.
1699 : : */
1700 : 90 : newestPage = SLRU_PAGES_PER_SEGMENT;
1701 : 90 : newestXact = newestPage * per_page + offset;
1702 [ + - ]: 90 : Assert(newestXact / per_page == newestPage);
1703 : 90 : oldestXact = newestXact + 1;
1704 : 90 : oldestXact -= 1U << 31;
1705 : 90 : oldestPage = oldestXact / per_page;
1706 [ + - ]: 90 : Assert(!SlruMayDeleteSegment(ctl,
1707 : : (newestPage -
1708 : : newestPage % SLRU_PAGES_PER_SEGMENT),
1709 : : oldestPage));
1710 : 90 : }
1711 : :
1712 : : /*
1713 : : * Unit-test a PagePrecedes function.
1714 : : *
1715 : : * This assumes every uint32 >= FirstNormalTransactionId is a valid key. It
1716 : : * assumes each value occupies a contiguous, fixed-size region of SLRU bytes.
1717 : : * (MultiXactMemberCtl separates flags from XIDs. NotifyCtl has
1718 : : * variable-length entries, no keys, and no random access. These unit tests
1719 : : * do not apply to them.)
1720 : : */
1721 : : void
1722 : 30 : SlruPagePrecedesUnitTests(SlruCtl ctl, int per_page)
1723 : : {
1724 : : /* Test first, middle and last entries of a page. */
1725 : 30 : SlruPagePrecedesTestOffset(ctl, per_page, 0);
1726 : 30 : SlruPagePrecedesTestOffset(ctl, per_page, per_page / 2);
1727 : 30 : SlruPagePrecedesTestOffset(ctl, per_page, per_page - 1);
1728 : 30 : }
1729 : : #endif
1730 : :
1731 : : /*
1732 : : * SlruScanDirectory callback
1733 : : * This callback reports true if there's any segment wholly prior to the
1734 : : * one containing the page passed as "data".
1735 : : */
1736 : : bool
1737 : 2 : SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int64 segpage,
1738 : : void *data)
1739 : : {
1740 : 2 : int64 cutoffPage = *(int64 *) data;
1741 : :
1742 [ - + ]: 2 : if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
1743 : 0 : return true; /* found one; don't iterate any more */
1744 : :
1745 : 2 : return false; /* keep going */
1746 : 2 : }
1747 : :
1748 : : /*
1749 : : * SlruScanDirectory callback.
1750 : : * This callback deletes segments prior to the one passed in as "data".
1751 : : */
1752 : : static bool
1753 : 7 : SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int64 segpage,
1754 : : void *data)
1755 : : {
1756 : 7 : int64 cutoffPage = *(int64 *) data;
1757 : :
1758 [ + - ]: 7 : if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
1759 : 0 : SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
1760 : :
1761 : 7 : return false; /* keep going */
1762 : 7 : }
1763 : :
1764 : : /*
1765 : : * SlruScanDirectory callback.
1766 : : * This callback deletes all segments.
1767 : : */
1768 : : bool
1769 : 0 : SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int64 segpage, void *data)
1770 : : {
1771 : 0 : SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
1772 : :
1773 : 0 : return false; /* keep going */
1774 : : }
1775 : :
1776 : : /*
1777 : : * An internal function used by SlruScanDirectory().
1778 : : *
1779 : : * Returns true if a file with a name of a given length may be a correct
1780 : : * SLRU segment.
1781 : : */
1782 : : static inline bool
1783 : 51 : SlruCorrectSegmentFilenameLength(SlruCtl ctl, size_t len)
1784 : : {
1785 [ + + ]: 51 : if (ctl->long_segment_names)
1786 : 12 : return (len == 15); /* see SlruFileName() */
1787 : : else
1788 : :
1789 : : /*
1790 : : * Commit 638cf09e76d allowed 5-character lengths. Later commit
1791 : : * 73c986adde5 allowed 6-character length.
1792 : : *
1793 : : * Note: There is an ongoing plan to migrate all SLRUs to 64-bit page
1794 : : * numbers, and the corresponding 15-character file names, which may
1795 : : * eventually deprecate the support for 4, 5, and 6-character names.
1796 : : */
1797 [ + + - + ]: 39 : return (len == 4 || len == 5 || len == 6);
1798 : 51 : }
1799 : :
1800 : : /*
1801 : : * Scan the SimpleLru directory and apply a callback to each file found in it.
1802 : : *
1803 : : * If the callback returns true, the scan is stopped. The last return value
1804 : : * from the callback is returned.
1805 : : *
1806 : : * The callback receives the following arguments: 1. the SlruCtl struct for the
1807 : : * slru being truncated; 2. the filename being considered; 3. the page number
1808 : : * for the first page of that file; 4. a pointer to the opaque data given to us
1809 : : * by the caller.
1810 : : *
1811 : : * Note that the ordering in which the directory is scanned is not guaranteed.
1812 : : *
1813 : : * Note that no locking is applied.
1814 : : */
1815 : : bool
1816 : 21 : SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)
1817 : : {
1818 : 21 : bool retval = false;
1819 : 21 : DIR *cldir;
1820 : 21 : struct dirent *clde;
1821 : 21 : int64 segno;
1822 : 21 : int64 segpage;
1823 : :
1824 : 21 : cldir = AllocateDir(ctl->Dir);
1825 [ + + ]: 72 : while ((clde = ReadDir(cldir, ctl->Dir)) != NULL)
1826 : : {
1827 : 51 : size_t len;
1828 : :
1829 : 51 : len = strlen(clde->d_name);
1830 : :
1831 [ + + - + ]: 51 : if (SlruCorrectSegmentFilenameLength(ctl, len) &&
1832 : 9 : strspn(clde->d_name, "0123456789ABCDEF") == len)
1833 : : {
1834 : 9 : segno = strtoi64(clde->d_name, NULL, 16);
1835 : 9 : segpage = segno * SLRU_PAGES_PER_SEGMENT;
1836 : :
1837 [ - + - + ]: 9 : elog(DEBUG2, "SlruScanDirectory invoking callback on %s/%s",
1838 : : ctl->Dir, clde->d_name);
1839 : 9 : retval = callback(ctl, clde->d_name, segpage, data);
1840 [ - + ]: 9 : if (retval)
1841 : 0 : break;
1842 : 9 : }
1843 [ - - + ]: 51 : }
1844 : 21 : FreeDir(cldir);
1845 : :
1846 : 42 : return retval;
1847 : 21 : }
1848 : :
1849 : : /*
1850 : : * Individual SLRUs (clog, ...) have to provide a sync.c handler function so
1851 : : * that they can provide the correct "SlruCtl" (otherwise we don't know how to
1852 : : * build the path), but they just forward to this common implementation that
1853 : : * performs the fsync.
1854 : : */
1855 : : int
1856 : 0 : SlruSyncFileTag(SlruCtl ctl, const FileTag *ftag, char *path)
1857 : : {
1858 : 0 : int fd;
1859 : 0 : int save_errno;
1860 : 0 : int result;
1861 : :
1862 : 0 : SlruFileName(ctl, path, ftag->segno);
1863 : :
1864 : 0 : fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
1865 [ # # ]: 0 : if (fd < 0)
1866 : 0 : return -1;
1867 : :
1868 : 0 : pgstat_report_wait_start(WAIT_EVENT_SLRU_FLUSH_SYNC);
1869 : 0 : result = pg_fsync(fd);
1870 : 0 : pgstat_report_wait_end();
1871 : 0 : save_errno = errno;
1872 : :
1873 : 0 : CloseTransientFile(fd);
1874 : :
1875 : 0 : errno = save_errno;
1876 : 0 : return result;
1877 : 0 : }
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