Line data Source code
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) 1996-2025, 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 14925416 : SlruFileName(SlruCtl ctl, char *path, int64 segno)
92 : {
93 14925416 : 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 : Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFFFFFFFFFFF));
103 294 : 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 : Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFF));
112 14925122 : return snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir,
113 : (unsigned int) segno);
114 : }
115 : }
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 41966 : SimpleLruShmemSize(int nslots, int nlsns)
199 : {
200 41966 : int nbanks = nslots / SLRU_BANK_SIZE;
201 : Size sz;
202 :
203 : Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
204 : Assert(nslots % SLRU_BANK_SIZE == 0);
205 :
206 : /* we assume nslots isn't so large as to risk overflow */
207 41966 : sz = MAXALIGN(sizeof(SlruSharedData));
208 41966 : sz += MAXALIGN(nslots * sizeof(char *)); /* page_buffer[] */
209 41966 : sz += MAXALIGN(nslots * sizeof(SlruPageStatus)); /* page_status[] */
210 41966 : sz += MAXALIGN(nslots * sizeof(bool)); /* page_dirty[] */
211 41966 : sz += MAXALIGN(nslots * sizeof(int64)); /* page_number[] */
212 41966 : sz += MAXALIGN(nslots * sizeof(int)); /* page_lru_count[] */
213 41966 : sz += MAXALIGN(nslots * sizeof(LWLockPadded)); /* buffer_locks[] */
214 41966 : sz += MAXALIGN(nbanks * sizeof(LWLockPadded)); /* bank_locks[] */
215 41966 : sz += MAXALIGN(nbanks * sizeof(int)); /* bank_cur_lru_count[] */
216 :
217 41966 : if (nlsns > 0)
218 5994 : sz += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr)); /* group_lsn[] */
219 :
220 41966 : return BUFFERALIGN(sz) + BLCKSZ * nslots;
221 : }
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 17880 : SimpleLruAutotuneBuffers(int divisor, int max)
232 : {
233 17880 : 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 : */
250 : void
251 14676 : SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
252 : const char *subdir, int buffer_tranche_id, int bank_tranche_id,
253 : SyncRequestHandler sync_handler, bool long_segment_names)
254 : {
255 : SlruShared shared;
256 : bool found;
257 14676 : int nbanks = nslots / SLRU_BANK_SIZE;
258 :
259 : Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
260 :
261 14676 : shared = (SlruShared) ShmemInitStruct(name,
262 : SimpleLruShmemSize(nslots, nlsns),
263 : &found);
264 :
265 14676 : if (!IsUnderPostmaster)
266 : {
267 : /* Initialize locks and shared memory area */
268 : char *ptr;
269 : Size offset;
270 :
271 : Assert(!found);
272 :
273 14676 : memset(shared, 0, sizeof(SlruSharedData));
274 :
275 14676 : shared->num_slots = nslots;
276 14676 : shared->lsn_groups_per_page = nlsns;
277 :
278 14676 : pg_atomic_init_u64(&shared->latest_page_number, 0);
279 :
280 14676 : shared->slru_stats_idx = pgstat_get_slru_index(name);
281 :
282 14676 : ptr = (char *) shared;
283 14676 : offset = MAXALIGN(sizeof(SlruSharedData));
284 14676 : shared->page_buffer = (char **) (ptr + offset);
285 14676 : offset += MAXALIGN(nslots * sizeof(char *));
286 14676 : shared->page_status = (SlruPageStatus *) (ptr + offset);
287 14676 : offset += MAXALIGN(nslots * sizeof(SlruPageStatus));
288 14676 : shared->page_dirty = (bool *) (ptr + offset);
289 14676 : offset += MAXALIGN(nslots * sizeof(bool));
290 14676 : shared->page_number = (int64 *) (ptr + offset);
291 14676 : offset += MAXALIGN(nslots * sizeof(int64));
292 14676 : shared->page_lru_count = (int *) (ptr + offset);
293 14676 : offset += MAXALIGN(nslots * sizeof(int));
294 :
295 : /* Initialize LWLocks */
296 14676 : shared->buffer_locks = (LWLockPadded *) (ptr + offset);
297 14676 : offset += MAXALIGN(nslots * sizeof(LWLockPadded));
298 14676 : shared->bank_locks = (LWLockPadded *) (ptr + offset);
299 14676 : offset += MAXALIGN(nbanks * sizeof(LWLockPadded));
300 14676 : shared->bank_cur_lru_count = (int *) (ptr + offset);
301 14676 : offset += MAXALIGN(nbanks * sizeof(int));
302 :
303 14676 : if (nlsns > 0)
304 : {
305 2096 : shared->group_lsn = (XLogRecPtr *) (ptr + offset);
306 2096 : offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));
307 : }
308 :
309 14676 : ptr += BUFFERALIGN(offset);
310 375348 : for (int slotno = 0; slotno < nslots; slotno++)
311 : {
312 360672 : LWLockInitialize(&shared->buffer_locks[slotno].lock,
313 : buffer_tranche_id);
314 :
315 360672 : shared->page_buffer[slotno] = ptr;
316 360672 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
317 360672 : shared->page_dirty[slotno] = false;
318 360672 : shared->page_lru_count[slotno] = 0;
319 360672 : ptr += BLCKSZ;
320 : }
321 :
322 : /* Initialize the slot banks. */
323 37218 : for (int bankno = 0; bankno < nbanks; bankno++)
324 : {
325 22542 : LWLockInitialize(&shared->bank_locks[bankno].lock, bank_tranche_id);
326 22542 : shared->bank_cur_lru_count[bankno] = 0;
327 : }
328 :
329 : /* Should fit to estimated shmem size */
330 : Assert(ptr - (char *) shared <= SimpleLruShmemSize(nslots, nlsns));
331 : }
332 : else
333 : {
334 : Assert(found);
335 : Assert(shared->num_slots == nslots);
336 : }
337 :
338 : /*
339 : * Initialize the unshared control struct, including directory path. We
340 : * assume caller set PagePrecedes.
341 : */
342 14676 : ctl->shared = shared;
343 14676 : ctl->sync_handler = sync_handler;
344 14676 : ctl->long_segment_names = long_segment_names;
345 14676 : ctl->nbanks = nbanks;
346 14676 : strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir));
347 14676 : }
348 :
349 : /*
350 : * Helper function for GUC check_hook to check whether slru buffers are in
351 : * multiples of SLRU_BANK_SIZE.
352 : */
353 : bool
354 21444 : check_slru_buffers(const char *name, int *newval)
355 : {
356 : /* Valid values are multiples of SLRU_BANK_SIZE */
357 21444 : if (*newval % SLRU_BANK_SIZE == 0)
358 21444 : return true;
359 :
360 0 : GUC_check_errdetail("\"%s\" must be a multiple of %d.", name,
361 : SLRU_BANK_SIZE);
362 0 : return false;
363 : }
364 :
365 : /*
366 : * Initialize (or reinitialize) a page to zeroes.
367 : *
368 : * The page is not actually written, just set up in shared memory.
369 : * The slot number of the new page is returned.
370 : *
371 : * Bank lock must be held at entry, and will be held at exit.
372 : */
373 : int
374 14679114 : SimpleLruZeroPage(SlruCtl ctl, int64 pageno)
375 : {
376 14679114 : SlruShared shared = ctl->shared;
377 : int slotno;
378 :
379 : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
380 :
381 : /* Find a suitable buffer slot for the page */
382 14679114 : slotno = SlruSelectLRUPage(ctl, pageno);
383 : Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
384 : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
385 : !shared->page_dirty[slotno]) ||
386 : shared->page_number[slotno] == pageno);
387 :
388 : /* Mark the slot as containing this page */
389 14679114 : shared->page_number[slotno] = pageno;
390 14679114 : shared->page_status[slotno] = SLRU_PAGE_VALID;
391 14679114 : shared->page_dirty[slotno] = true;
392 14679114 : SlruRecentlyUsed(shared, slotno);
393 :
394 : /* Set the buffer to zeroes */
395 14679114 : MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
396 :
397 : /* Set the LSNs for this new page to zero */
398 14679114 : SimpleLruZeroLSNs(ctl, slotno);
399 :
400 : /*
401 : * Assume this page is now the latest active page.
402 : *
403 : * Note that because both this routine and SlruSelectLRUPage run with
404 : * ControlLock held, it is not possible for this to be zeroing a page that
405 : * SlruSelectLRUPage is going to evict simultaneously. Therefore, there's
406 : * no memory barrier here.
407 : */
408 14679114 : pg_atomic_write_u64(&shared->latest_page_number, pageno);
409 :
410 : /* update the stats counter of zeroed pages */
411 14679114 : pgstat_count_slru_page_zeroed(shared->slru_stats_idx);
412 :
413 14679114 : return slotno;
414 : }
415 :
416 : /*
417 : * Zero all the LSNs we store for this slru page.
418 : *
419 : * This should be called each time we create a new page, and each time we read
420 : * in a page from disk into an existing buffer. (Such an old page cannot
421 : * have any interesting LSNs, since we'd have flushed them before writing
422 : * the page in the first place.)
423 : *
424 : * This assumes that InvalidXLogRecPtr is bitwise-all-0.
425 : */
426 : static void
427 14682970 : SimpleLruZeroLSNs(SlruCtl ctl, int slotno)
428 : {
429 14682970 : SlruShared shared = ctl->shared;
430 :
431 14682970 : if (shared->lsn_groups_per_page > 0)
432 865650 : MemSet(&shared->group_lsn[slotno * shared->lsn_groups_per_page], 0,
433 : shared->lsn_groups_per_page * sizeof(XLogRecPtr));
434 14682970 : }
435 :
436 : /*
437 : * Wait for any active I/O on a page slot to finish. (This does not
438 : * guarantee that new I/O hasn't been started before we return, though.
439 : * In fact the slot might not even contain the same page anymore.)
440 : *
441 : * Bank lock must be held at entry, and will be held at exit.
442 : */
443 : static void
444 6 : SimpleLruWaitIO(SlruCtl ctl, int slotno)
445 : {
446 6 : SlruShared shared = ctl->shared;
447 6 : int bankno = SlotGetBankNumber(slotno);
448 :
449 : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
450 :
451 : /* See notes at top of file */
452 6 : LWLockRelease(&shared->bank_locks[bankno].lock);
453 6 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED);
454 6 : LWLockRelease(&shared->buffer_locks[slotno].lock);
455 6 : LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
456 :
457 : /*
458 : * If the slot is still in an io-in-progress state, then either someone
459 : * already started a new I/O on the slot, or a previous I/O failed and
460 : * neglected to reset the page state. That shouldn't happen, really, but
461 : * it seems worth a few extra cycles to check and recover from it. We can
462 : * cheaply test for failure by seeing if the buffer lock is still held (we
463 : * assume that transaction abort would release the lock).
464 : */
465 6 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
466 6 : shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS)
467 : {
468 0 : if (LWLockConditionalAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED))
469 : {
470 : /* indeed, the I/O must have failed */
471 0 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS)
472 0 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
473 : else /* write_in_progress */
474 : {
475 0 : shared->page_status[slotno] = SLRU_PAGE_VALID;
476 0 : shared->page_dirty[slotno] = true;
477 : }
478 0 : LWLockRelease(&shared->buffer_locks[slotno].lock);
479 : }
480 : }
481 6 : }
482 :
483 : /*
484 : * Find a page in a shared buffer, reading it in if necessary.
485 : * The page number must correspond to an already-initialized page.
486 : *
487 : * If write_ok is true then it is OK to return a page that is in
488 : * WRITE_IN_PROGRESS state; it is the caller's responsibility to be sure
489 : * that modification of the page is safe. If write_ok is false then we
490 : * will not return the page until it is not undergoing active I/O.
491 : *
492 : * The passed-in xid is used only for error reporting, and may be
493 : * InvalidTransactionId if no specific xid is associated with the action.
494 : *
495 : * Return value is the shared-buffer slot number now holding the page.
496 : * The buffer's LRU access info is updated.
497 : *
498 : * The correct bank lock must be held at entry, and will be held at exit.
499 : */
500 : int
501 330836 : SimpleLruReadPage(SlruCtl ctl, int64 pageno, bool write_ok,
502 : TransactionId xid)
503 : {
504 330836 : SlruShared shared = ctl->shared;
505 330836 : LWLock *banklock = SimpleLruGetBankLock(ctl, pageno);
506 :
507 : Assert(LWLockHeldByMeInMode(banklock, LW_EXCLUSIVE));
508 :
509 : /* Outer loop handles restart if we must wait for someone else's I/O */
510 : for (;;)
511 4 : {
512 : int slotno;
513 : bool ok;
514 :
515 : /* See if page already is in memory; if not, pick victim slot */
516 330840 : slotno = SlruSelectLRUPage(ctl, pageno);
517 :
518 : /* Did we find the page in memory? */
519 330840 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
520 327532 : shared->page_number[slotno] == pageno)
521 : {
522 : /*
523 : * If page is still being read in, we must wait for I/O. Likewise
524 : * if the page is being written and the caller said that's not OK.
525 : */
526 326984 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
527 326984 : (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
528 8 : !write_ok))
529 : {
530 4 : SimpleLruWaitIO(ctl, slotno);
531 : /* Now we must recheck state from the top */
532 4 : continue;
533 : }
534 : /* Otherwise, it's ready to use */
535 326980 : SlruRecentlyUsed(shared, slotno);
536 :
537 : /* update the stats counter of pages found in the SLRU */
538 326980 : pgstat_count_slru_page_hit(shared->slru_stats_idx);
539 :
540 326980 : return slotno;
541 : }
542 :
543 : /* We found no match; assert we selected a freeable slot */
544 : Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
545 : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
546 : !shared->page_dirty[slotno]));
547 :
548 : /* Mark the slot read-busy */
549 3856 : shared->page_number[slotno] = pageno;
550 3856 : shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS;
551 3856 : shared->page_dirty[slotno] = false;
552 :
553 : /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
554 3856 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
555 :
556 : /* Release bank lock while doing I/O */
557 3856 : LWLockRelease(banklock);
558 :
559 : /* Do the read */
560 3856 : ok = SlruPhysicalReadPage(ctl, pageno, slotno);
561 :
562 : /* Set the LSNs for this newly read-in page to zero */
563 3856 : SimpleLruZeroLSNs(ctl, slotno);
564 :
565 : /* Re-acquire bank control lock and update page state */
566 3856 : LWLockAcquire(banklock, LW_EXCLUSIVE);
567 :
568 : Assert(shared->page_number[slotno] == pageno &&
569 : shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS &&
570 : !shared->page_dirty[slotno]);
571 :
572 3856 : shared->page_status[slotno] = ok ? SLRU_PAGE_VALID : SLRU_PAGE_EMPTY;
573 :
574 3856 : LWLockRelease(&shared->buffer_locks[slotno].lock);
575 :
576 : /* Now it's okay to ereport if we failed */
577 3856 : if (!ok)
578 0 : SlruReportIOError(ctl, pageno, xid);
579 :
580 3856 : SlruRecentlyUsed(shared, slotno);
581 :
582 : /* update the stats counter of pages not found in SLRU */
583 3856 : pgstat_count_slru_page_read(shared->slru_stats_idx);
584 :
585 3856 : return slotno;
586 : }
587 : }
588 :
589 : /*
590 : * Find a page in a shared buffer, reading it in if necessary.
591 : * The page number must correspond to an already-initialized page.
592 : * The caller must intend only read-only access to the page.
593 : *
594 : * The passed-in xid is used only for error reporting, and may be
595 : * InvalidTransactionId if no specific xid is associated with the action.
596 : *
597 : * Return value is the shared-buffer slot number now holding the page.
598 : * The buffer's LRU access info is updated.
599 : *
600 : * Bank control lock must NOT be held at entry, but will be held at exit.
601 : * It is unspecified whether the lock will be shared or exclusive.
602 : */
603 : int
604 1462982 : SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
605 : {
606 1462982 : SlruShared shared = ctl->shared;
607 1462982 : LWLock *banklock = SimpleLruGetBankLock(ctl, pageno);
608 1462982 : int bankno = pageno % ctl->nbanks;
609 1462982 : int bankstart = bankno * SLRU_BANK_SIZE;
610 1462982 : int bankend = bankstart + SLRU_BANK_SIZE;
611 :
612 : /* Try to find the page while holding only shared lock */
613 1462982 : LWLockAcquire(banklock, LW_SHARED);
614 :
615 : /* See if page is already in a buffer */
616 1476136 : for (int slotno = bankstart; slotno < bankend; slotno++)
617 : {
618 1475712 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
619 1473910 : shared->page_number[slotno] == pageno &&
620 1462558 : shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
621 : {
622 : /* See comments for SlruRecentlyUsed macro */
623 1462558 : SlruRecentlyUsed(shared, slotno);
624 :
625 : /* update the stats counter of pages found in the SLRU */
626 1462558 : pgstat_count_slru_page_hit(shared->slru_stats_idx);
627 :
628 1462558 : return slotno;
629 : }
630 : }
631 :
632 : /* No luck, so switch to normal exclusive lock and do regular read */
633 424 : LWLockRelease(banklock);
634 424 : LWLockAcquire(banklock, LW_EXCLUSIVE);
635 :
636 424 : return SimpleLruReadPage(ctl, pageno, true, xid);
637 : }
638 :
639 : /*
640 : * Write a page from a shared buffer, if necessary.
641 : * Does nothing if the specified slot is not dirty.
642 : *
643 : * NOTE: only one write attempt is made here. Hence, it is possible that
644 : * the page is still dirty at exit (if someone else re-dirtied it during
645 : * the write). However, we *do* attempt a fresh write even if the page
646 : * is already being written; this is for checkpoints.
647 : *
648 : * Bank lock must be held at entry, and will be held at exit.
649 : */
650 : static void
651 14687322 : SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata)
652 : {
653 14687322 : SlruShared shared = ctl->shared;
654 14687322 : int64 pageno = shared->page_number[slotno];
655 14687322 : int bankno = SlotGetBankNumber(slotno);
656 : bool ok;
657 :
658 : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
659 : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
660 :
661 : /* If a write is in progress, wait for it to finish */
662 14687324 : while (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
663 2 : shared->page_number[slotno] == pageno)
664 : {
665 2 : SimpleLruWaitIO(ctl, slotno);
666 : }
667 :
668 : /*
669 : * Do nothing if page is not dirty, or if buffer no longer contains the
670 : * same page we were called for.
671 : */
672 14687322 : if (!shared->page_dirty[slotno] ||
673 14681866 : shared->page_status[slotno] != SLRU_PAGE_VALID ||
674 14681866 : shared->page_number[slotno] != pageno)
675 5456 : return;
676 :
677 : /*
678 : * Mark the slot write-busy, and clear the dirtybit. After this point, a
679 : * transaction status update on this page will mark it dirty again.
680 : */
681 14681866 : shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS;
682 14681866 : shared->page_dirty[slotno] = false;
683 :
684 : /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
685 14681866 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
686 :
687 : /* Release bank lock while doing I/O */
688 14681866 : LWLockRelease(&shared->bank_locks[bankno].lock);
689 :
690 : /* Do the write */
691 14681866 : ok = SlruPhysicalWritePage(ctl, pageno, slotno, fdata);
692 :
693 : /* If we failed, and we're in a flush, better close the files */
694 14681866 : if (!ok && fdata)
695 : {
696 0 : for (int i = 0; i < fdata->num_files; i++)
697 0 : CloseTransientFile(fdata->fd[i]);
698 : }
699 :
700 : /* Re-acquire bank lock and update page state */
701 14681866 : LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
702 :
703 : Assert(shared->page_number[slotno] == pageno &&
704 : shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS);
705 :
706 : /* If we failed to write, mark the page dirty again */
707 14681866 : if (!ok)
708 0 : shared->page_dirty[slotno] = true;
709 :
710 14681866 : shared->page_status[slotno] = SLRU_PAGE_VALID;
711 :
712 14681866 : LWLockRelease(&shared->buffer_locks[slotno].lock);
713 :
714 : /* Now it's okay to ereport if we failed */
715 14681866 : if (!ok)
716 0 : SlruReportIOError(ctl, pageno, InvalidTransactionId);
717 :
718 : /* If part of a checkpoint, count this as a SLRU buffer written. */
719 14681866 : if (fdata)
720 : {
721 5122 : CheckpointStats.ckpt_slru_written++;
722 5122 : PendingCheckpointerStats.slru_written++;
723 : }
724 : }
725 :
726 : /*
727 : * Wrapper of SlruInternalWritePage, for external callers.
728 : * fdata is always passed a NULL here.
729 : */
730 : void
731 616 : SimpleLruWritePage(SlruCtl ctl, int slotno)
732 : {
733 : Assert(ctl->shared->page_status[slotno] != SLRU_PAGE_EMPTY);
734 :
735 616 : SlruInternalWritePage(ctl, slotno, NULL);
736 616 : }
737 :
738 : /*
739 : * Return whether the given page exists on disk.
740 : *
741 : * A false return means that either the file does not exist, or that it's not
742 : * large enough to contain the given page.
743 : */
744 : bool
745 200 : SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int64 pageno)
746 : {
747 200 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
748 200 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
749 200 : int offset = rpageno * BLCKSZ;
750 : char path[MAXPGPATH];
751 : int fd;
752 : bool result;
753 : off_t endpos;
754 :
755 : /* update the stats counter of checked pages */
756 200 : pgstat_count_slru_page_exists(ctl->shared->slru_stats_idx);
757 :
758 200 : SlruFileName(ctl, path, segno);
759 :
760 200 : fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
761 200 : if (fd < 0)
762 : {
763 : /* expected: file doesn't exist */
764 48 : if (errno == ENOENT)
765 48 : return false;
766 :
767 : /* report error normally */
768 0 : slru_errcause = SLRU_OPEN_FAILED;
769 0 : slru_errno = errno;
770 0 : SlruReportIOError(ctl, pageno, 0);
771 : }
772 :
773 152 : if ((endpos = lseek(fd, 0, SEEK_END)) < 0)
774 : {
775 0 : slru_errcause = SLRU_SEEK_FAILED;
776 0 : slru_errno = errno;
777 0 : SlruReportIOError(ctl, pageno, 0);
778 : }
779 :
780 152 : result = endpos >= (off_t) (offset + BLCKSZ);
781 :
782 152 : if (CloseTransientFile(fd) != 0)
783 : {
784 0 : slru_errcause = SLRU_CLOSE_FAILED;
785 0 : slru_errno = errno;
786 0 : return false;
787 : }
788 :
789 152 : return result;
790 : }
791 :
792 : /*
793 : * Physical read of a (previously existing) page into a buffer slot
794 : *
795 : * On failure, we cannot just ereport(ERROR) since caller has put state in
796 : * shared memory that must be undone. So, we return false and save enough
797 : * info in static variables to let SlruReportIOError make the report.
798 : *
799 : * For now, assume it's not worth keeping a file pointer open across
800 : * read/write operations. We could cache one virtual file pointer ...
801 : */
802 : static bool
803 3856 : SlruPhysicalReadPage(SlruCtl ctl, int64 pageno, int slotno)
804 : {
805 3856 : SlruShared shared = ctl->shared;
806 3856 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
807 3856 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
808 3856 : off_t offset = rpageno * BLCKSZ;
809 : char path[MAXPGPATH];
810 : int fd;
811 :
812 3856 : SlruFileName(ctl, path, segno);
813 :
814 : /*
815 : * In a crash-and-restart situation, it's possible for us to receive
816 : * commands to set the commit status of transactions whose bits are in
817 : * already-truncated segments of the commit log (see notes in
818 : * SlruPhysicalWritePage). Hence, if we are InRecovery, allow the case
819 : * where the file doesn't exist, and return zeroes instead.
820 : */
821 3856 : fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
822 3856 : if (fd < 0)
823 : {
824 0 : if (errno != ENOENT || !InRecovery)
825 : {
826 0 : slru_errcause = SLRU_OPEN_FAILED;
827 0 : slru_errno = errno;
828 0 : return false;
829 : }
830 :
831 0 : ereport(LOG,
832 : (errmsg("file \"%s\" doesn't exist, reading as zeroes",
833 : path)));
834 0 : MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
835 0 : return true;
836 : }
837 :
838 3856 : errno = 0;
839 3856 : pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
840 3856 : if (pg_pread(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
841 : {
842 0 : pgstat_report_wait_end();
843 0 : slru_errcause = SLRU_READ_FAILED;
844 0 : slru_errno = errno;
845 0 : CloseTransientFile(fd);
846 0 : return false;
847 : }
848 3856 : pgstat_report_wait_end();
849 :
850 3856 : if (CloseTransientFile(fd) != 0)
851 : {
852 0 : slru_errcause = SLRU_CLOSE_FAILED;
853 0 : slru_errno = errno;
854 0 : return false;
855 : }
856 :
857 3856 : return true;
858 : }
859 :
860 : /*
861 : * Physical write of a page from a buffer slot
862 : *
863 : * On failure, we cannot just ereport(ERROR) since caller has put state in
864 : * shared memory that must be undone. So, we return false and save enough
865 : * info in static variables to let SlruReportIOError make the report.
866 : *
867 : * For now, assume it's not worth keeping a file pointer open across
868 : * independent read/write operations. We do batch operations during
869 : * SimpleLruWriteAll, though.
870 : *
871 : * fdata is NULL for a standalone write, pointer to open-file info during
872 : * SimpleLruWriteAll.
873 : */
874 : static bool
875 14681866 : SlruPhysicalWritePage(SlruCtl ctl, int64 pageno, int slotno, SlruWriteAll fdata)
876 : {
877 14681866 : SlruShared shared = ctl->shared;
878 14681866 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
879 14681866 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
880 14681866 : off_t offset = rpageno * BLCKSZ;
881 : char path[MAXPGPATH];
882 14681866 : int fd = -1;
883 :
884 : /* update the stats counter of written pages */
885 14681866 : pgstat_count_slru_page_written(shared->slru_stats_idx);
886 :
887 : /*
888 : * Honor the write-WAL-before-data rule, if appropriate, so that we do not
889 : * write out data before associated WAL records. This is the same action
890 : * performed during FlushBuffer() in the main buffer manager.
891 : */
892 14681866 : if (shared->group_lsn != NULL)
893 : {
894 : /*
895 : * We must determine the largest async-commit LSN for the page. This
896 : * is a bit tedious, but since this entire function is a slow path
897 : * anyway, it seems better to do this here than to maintain a per-page
898 : * LSN variable (which'd need an extra comparison in the
899 : * transaction-commit path).
900 : */
901 : XLogRecPtr max_lsn;
902 : int lsnindex;
903 :
904 865816 : lsnindex = slotno * shared->lsn_groups_per_page;
905 865816 : max_lsn = shared->group_lsn[lsnindex++];
906 886595584 : for (int lsnoff = 1; lsnoff < shared->lsn_groups_per_page; lsnoff++)
907 : {
908 885729768 : XLogRecPtr this_lsn = shared->group_lsn[lsnindex++];
909 :
910 885729768 : if (max_lsn < this_lsn)
911 82600 : max_lsn = this_lsn;
912 : }
913 :
914 865816 : if (!XLogRecPtrIsInvalid(max_lsn))
915 : {
916 : /*
917 : * As noted above, elog(ERROR) is not acceptable here, so if
918 : * XLogFlush were to fail, we must PANIC. This isn't much of a
919 : * restriction because XLogFlush is just about all critical
920 : * section anyway, but let's make sure.
921 : */
922 972 : START_CRIT_SECTION();
923 972 : XLogFlush(max_lsn);
924 972 : END_CRIT_SECTION();
925 : }
926 : }
927 :
928 : /*
929 : * During a SimpleLruWriteAll, we may already have the desired file open.
930 : */
931 14681866 : if (fdata)
932 : {
933 5272 : for (int i = 0; i < fdata->num_files; i++)
934 : {
935 588 : if (fdata->segno[i] == segno)
936 : {
937 438 : fd = fdata->fd[i];
938 438 : break;
939 : }
940 : }
941 : }
942 :
943 14681866 : if (fd < 0)
944 : {
945 : /*
946 : * If the file doesn't already exist, we should create it. It is
947 : * possible for this to need to happen when writing a page that's not
948 : * first in its segment; we assume the OS can cope with that. (Note:
949 : * it might seem that it'd be okay to create files only when
950 : * SimpleLruZeroPage is called for the first page of a segment.
951 : * However, if after a crash and restart the REDO logic elects to
952 : * replay the log from a checkpoint before the latest one, then it's
953 : * possible that we will get commands to set transaction status of
954 : * transactions that have already been truncated from the commit log.
955 : * Easiest way to deal with that is to accept references to
956 : * nonexistent files here and in SlruPhysicalReadPage.)
957 : *
958 : * Note: it is possible for more than one backend to be executing this
959 : * code simultaneously for different pages of the same file. Hence,
960 : * don't use O_EXCL or O_TRUNC or anything like that.
961 : */
962 14681428 : SlruFileName(ctl, path, segno);
963 14681428 : fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY);
964 14681428 : if (fd < 0)
965 : {
966 0 : slru_errcause = SLRU_OPEN_FAILED;
967 0 : slru_errno = errno;
968 0 : return false;
969 : }
970 :
971 14681428 : if (fdata)
972 : {
973 4684 : if (fdata->num_files < MAX_WRITEALL_BUFFERS)
974 : {
975 4684 : fdata->fd[fdata->num_files] = fd;
976 4684 : fdata->segno[fdata->num_files] = segno;
977 4684 : fdata->num_files++;
978 : }
979 : else
980 : {
981 : /*
982 : * In the unlikely event that we exceed MAX_WRITEALL_BUFFERS,
983 : * fall back to treating it as a standalone write.
984 : */
985 0 : fdata = NULL;
986 : }
987 : }
988 : }
989 :
990 14681866 : errno = 0;
991 14681866 : pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE);
992 14681866 : if (pg_pwrite(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
993 : {
994 0 : pgstat_report_wait_end();
995 : /* if write didn't set errno, assume problem is no disk space */
996 0 : if (errno == 0)
997 0 : errno = ENOSPC;
998 0 : slru_errcause = SLRU_WRITE_FAILED;
999 0 : slru_errno = errno;
1000 0 : if (!fdata)
1001 0 : CloseTransientFile(fd);
1002 0 : return false;
1003 : }
1004 14681866 : pgstat_report_wait_end();
1005 :
1006 : /* Queue up a sync request for the checkpointer. */
1007 14681866 : if (ctl->sync_handler != SYNC_HANDLER_NONE)
1008 : {
1009 : FileTag tag;
1010 :
1011 867228 : INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
1012 867228 : if (!RegisterSyncRequest(&tag, SYNC_REQUEST, false))
1013 : {
1014 : /* No space to enqueue sync request. Do it synchronously. */
1015 0 : pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC);
1016 0 : if (pg_fsync(fd) != 0)
1017 : {
1018 0 : pgstat_report_wait_end();
1019 0 : slru_errcause = SLRU_FSYNC_FAILED;
1020 0 : slru_errno = errno;
1021 0 : CloseTransientFile(fd);
1022 0 : return false;
1023 : }
1024 0 : pgstat_report_wait_end();
1025 : }
1026 : }
1027 :
1028 : /* Close file, unless part of flush request. */
1029 14681866 : if (!fdata)
1030 : {
1031 14676744 : if (CloseTransientFile(fd) != 0)
1032 : {
1033 0 : slru_errcause = SLRU_CLOSE_FAILED;
1034 0 : slru_errno = errno;
1035 0 : return false;
1036 : }
1037 : }
1038 :
1039 14681866 : return true;
1040 : }
1041 :
1042 : /*
1043 : * Issue the error message after failure of SlruPhysicalReadPage or
1044 : * SlruPhysicalWritePage. Call this after cleaning up shared-memory state.
1045 : */
1046 : static void
1047 0 : SlruReportIOError(SlruCtl ctl, int64 pageno, TransactionId xid)
1048 : {
1049 0 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
1050 0 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
1051 0 : int offset = rpageno * BLCKSZ;
1052 : char path[MAXPGPATH];
1053 :
1054 0 : SlruFileName(ctl, path, segno);
1055 0 : errno = slru_errno;
1056 0 : switch (slru_errcause)
1057 : {
1058 0 : case SLRU_OPEN_FAILED:
1059 0 : ereport(ERROR,
1060 : (errcode_for_file_access(),
1061 : errmsg("could not access status of transaction %u", xid),
1062 : errdetail("Could not open file \"%s\": %m.", path)));
1063 : break;
1064 0 : case SLRU_SEEK_FAILED:
1065 0 : ereport(ERROR,
1066 : (errcode_for_file_access(),
1067 : errmsg("could not access status of transaction %u", xid),
1068 : errdetail("Could not seek in file \"%s\" to offset %d: %m.",
1069 : path, offset)));
1070 : break;
1071 0 : case SLRU_READ_FAILED:
1072 0 : if (errno)
1073 0 : ereport(ERROR,
1074 : (errcode_for_file_access(),
1075 : errmsg("could not access status of transaction %u", xid),
1076 : errdetail("Could not read from file \"%s\" at offset %d: %m.",
1077 : path, offset)));
1078 : else
1079 0 : ereport(ERROR,
1080 : (errmsg("could not access status of transaction %u", xid),
1081 : errdetail("Could not read from file \"%s\" at offset %d: read too few bytes.", path, offset)));
1082 : break;
1083 0 : case SLRU_WRITE_FAILED:
1084 0 : if (errno)
1085 0 : ereport(ERROR,
1086 : (errcode_for_file_access(),
1087 : errmsg("could not access status of transaction %u", xid),
1088 : errdetail("Could not write to file \"%s\" at offset %d: %m.",
1089 : path, offset)));
1090 : else
1091 0 : ereport(ERROR,
1092 : (errmsg("could not access status of transaction %u", xid),
1093 : errdetail("Could not write to file \"%s\" at offset %d: wrote too few bytes.",
1094 : path, offset)));
1095 : break;
1096 0 : case SLRU_FSYNC_FAILED:
1097 0 : ereport(data_sync_elevel(ERROR),
1098 : (errcode_for_file_access(),
1099 : errmsg("could not access status of transaction %u", xid),
1100 : errdetail("Could not fsync file \"%s\": %m.",
1101 : path)));
1102 0 : break;
1103 0 : case SLRU_CLOSE_FAILED:
1104 0 : ereport(ERROR,
1105 : (errcode_for_file_access(),
1106 : errmsg("could not access status of transaction %u", xid),
1107 : errdetail("Could not close file \"%s\": %m.",
1108 : path)));
1109 : break;
1110 0 : default:
1111 : /* can't get here, we trust */
1112 0 : elog(ERROR, "unrecognized SimpleLru error cause: %d",
1113 : (int) slru_errcause);
1114 : break;
1115 : }
1116 0 : }
1117 :
1118 : /*
1119 : * Mark a buffer slot "most recently used".
1120 : */
1121 : static inline void
1122 16472508 : SlruRecentlyUsed(SlruShared shared, int slotno)
1123 : {
1124 16472508 : int bankno = SlotGetBankNumber(slotno);
1125 16472508 : int new_lru_count = shared->bank_cur_lru_count[bankno];
1126 :
1127 : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
1128 :
1129 : /*
1130 : * The reason for the if-test is that there are often many consecutive
1131 : * accesses to the same page (particularly the latest page). By
1132 : * suppressing useless increments of bank_cur_lru_count, we reduce the
1133 : * probability that old pages' counts will "wrap around" and make them
1134 : * appear recently used.
1135 : *
1136 : * We allow this code to be executed concurrently by multiple processes
1137 : * within SimpleLruReadPage_ReadOnly(). As long as int reads and writes
1138 : * are atomic, this should not cause any completely-bogus values to enter
1139 : * the computation. However, it is possible for either bank_cur_lru_count
1140 : * or individual page_lru_count entries to be "reset" to lower values than
1141 : * they should have, in case a process is delayed while it executes this
1142 : * function. With care in SlruSelectLRUPage(), this does little harm, and
1143 : * in any case the absolute worst possible consequence is a nonoptimal
1144 : * choice of page to evict. The gain from allowing concurrent reads of
1145 : * SLRU pages seems worth it.
1146 : */
1147 16472508 : if (new_lru_count != shared->page_lru_count[slotno])
1148 : {
1149 14683220 : shared->bank_cur_lru_count[bankno] = ++new_lru_count;
1150 14683220 : shared->page_lru_count[slotno] = new_lru_count;
1151 : }
1152 16472508 : }
1153 :
1154 : /*
1155 : * Select the slot to re-use when we need a free slot for the given page.
1156 : *
1157 : * The target page number is passed not only because we need to know the
1158 : * correct bank to use, but also because we need to consider the possibility
1159 : * that some other process reads in the target page while we are doing I/O to
1160 : * free a slot. Hence, check or recheck to see if any slot already holds the
1161 : * target page, and return that slot if so. Thus, the returned slot is
1162 : * *either* a slot already holding the pageno (could be any state except
1163 : * EMPTY), *or* a freeable slot (state EMPTY or CLEAN).
1164 : *
1165 : * The correct bank lock must be held at entry, and will be held at exit.
1166 : */
1167 : static int
1168 15009954 : SlruSelectLRUPage(SlruCtl ctl, int64 pageno)
1169 : {
1170 15009954 : SlruShared shared = ctl->shared;
1171 :
1172 : /* Outer loop handles restart after I/O */
1173 : for (;;)
1174 14676060 : {
1175 : int cur_count;
1176 29686014 : int bestvalidslot = 0; /* keep compiler quiet */
1177 29686014 : int best_valid_delta = -1;
1178 29686014 : int64 best_valid_page_number = 0; /* keep compiler quiet */
1179 29686014 : int bestinvalidslot = 0; /* keep compiler quiet */
1180 29686014 : int best_invalid_delta = -1;
1181 29686014 : int64 best_invalid_page_number = 0; /* keep compiler quiet */
1182 29686014 : int bankno = pageno % ctl->nbanks;
1183 29686014 : int bankstart = bankno * SLRU_BANK_SIZE;
1184 29686014 : int bankend = bankstart + SLRU_BANK_SIZE;
1185 :
1186 : Assert(LWLockHeldByMe(SimpleLruGetBankLock(ctl, pageno)));
1187 :
1188 : /* See if page already has a buffer assigned */
1189 499428822 : for (int slotno = bankstart; slotno < bankend; slotno++)
1190 : {
1191 470070100 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
1192 469977218 : shared->page_number[slotno] == pageno)
1193 327292 : return slotno;
1194 : }
1195 :
1196 : /*
1197 : * If we find any EMPTY slot, just select that one. Else choose a
1198 : * victim page to replace. We normally take the least recently used
1199 : * valid page, but we will never take the slot containing
1200 : * latest_page_number, even if it appears least recently used. We
1201 : * will select a slot that is already I/O busy only if there is no
1202 : * other choice: a read-busy slot will not be least recently used once
1203 : * the read finishes, and waiting for an I/O on a write-busy slot is
1204 : * inferior to just picking some other slot. Testing shows the slot
1205 : * we pick instead will often be clean, allowing us to begin a read at
1206 : * once.
1207 : *
1208 : * Normally the page_lru_count values will all be different and so
1209 : * there will be a well-defined LRU page. But since we allow
1210 : * concurrent execution of SlruRecentlyUsed() within
1211 : * SimpleLruReadPage_ReadOnly(), it is possible that multiple pages
1212 : * acquire the same lru_count values. In that case we break ties by
1213 : * choosing the furthest-back page.
1214 : *
1215 : * Notice that this next line forcibly advances cur_lru_count to a
1216 : * value that is certainly beyond any value that will be in the
1217 : * page_lru_count array after the loop finishes. This ensures that
1218 : * the next execution of SlruRecentlyUsed will mark the page newly
1219 : * used, even if it's for a page that has the current counter value.
1220 : * That gets us back on the path to having good data when there are
1221 : * multiple pages with the same lru_count.
1222 : */
1223 29358722 : cur_count = (shared->bank_cur_lru_count[bankno])++;
1224 499005480 : for (int slotno = bankstart; slotno < bankend; slotno++)
1225 : {
1226 : int this_delta;
1227 : int64 this_page_number;
1228 :
1229 469652784 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1230 6026 : return slotno;
1231 :
1232 469646758 : this_delta = cur_count - shared->page_lru_count[slotno];
1233 469646758 : if (this_delta < 0)
1234 : {
1235 : /*
1236 : * Clean up in case shared updates have caused cur_count
1237 : * increments to get "lost". We back off the page counts,
1238 : * rather than trying to increase cur_count, to avoid any
1239 : * question of infinite loops or failure in the presence of
1240 : * wrapped-around counts.
1241 : */
1242 0 : shared->page_lru_count[slotno] = cur_count;
1243 0 : this_delta = 0;
1244 : }
1245 :
1246 : /*
1247 : * If this page is the one most recently zeroed, don't consider it
1248 : * an eviction candidate. See comments in SimpleLruZeroPage for an
1249 : * explanation about the lack of a memory barrier here.
1250 : */
1251 469646758 : this_page_number = shared->page_number[slotno];
1252 469646758 : if (this_page_number ==
1253 469646758 : pg_atomic_read_u64(&shared->latest_page_number))
1254 962 : continue;
1255 :
1256 469645796 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1257 : {
1258 469645546 : if (this_delta > best_valid_delta ||
1259 0 : (this_delta == best_valid_delta &&
1260 0 : ctl->PagePrecedes(this_page_number,
1261 : best_valid_page_number)))
1262 : {
1263 68263986 : bestvalidslot = slotno;
1264 68263986 : best_valid_delta = this_delta;
1265 68263986 : best_valid_page_number = this_page_number;
1266 : }
1267 : }
1268 : else
1269 : {
1270 250 : if (this_delta > best_invalid_delta ||
1271 0 : (this_delta == best_invalid_delta &&
1272 0 : ctl->PagePrecedes(this_page_number,
1273 : best_invalid_page_number)))
1274 : {
1275 250 : bestinvalidslot = slotno;
1276 250 : best_invalid_delta = this_delta;
1277 250 : best_invalid_page_number = this_page_number;
1278 : }
1279 : }
1280 : }
1281 :
1282 : /*
1283 : * If all pages (except possibly the latest one) are I/O busy, we'll
1284 : * have to wait for an I/O to complete and then retry. In that
1285 : * unhappy case, we choose to wait for the I/O on the least recently
1286 : * used slot, on the assumption that it was likely initiated first of
1287 : * all the I/Os in progress and may therefore finish first.
1288 : */
1289 29352696 : if (best_valid_delta < 0)
1290 : {
1291 0 : SimpleLruWaitIO(ctl, bestinvalidslot);
1292 0 : continue;
1293 : }
1294 :
1295 : /*
1296 : * If the selected page is clean, we're set.
1297 : */
1298 29352696 : if (!shared->page_dirty[bestvalidslot])
1299 14676636 : return bestvalidslot;
1300 :
1301 : /*
1302 : * Write the page.
1303 : */
1304 14676060 : SlruInternalWritePage(ctl, bestvalidslot, NULL);
1305 :
1306 : /*
1307 : * Now loop back and try again. This is the easiest way of dealing
1308 : * with corner cases such as the victim page being re-dirtied while we
1309 : * wrote it.
1310 : */
1311 : }
1312 : }
1313 :
1314 : /*
1315 : * Write dirty pages to disk during checkpoint or database shutdown. Flushing
1316 : * is deferred until the next call to ProcessSyncRequests(), though we do fsync
1317 : * the containing directory here to make sure that newly created directory
1318 : * entries are on disk.
1319 : */
1320 : void
1321 16630 : SimpleLruWriteAll(SlruCtl ctl, bool allow_redirtied)
1322 : {
1323 16630 : SlruShared shared = ctl->shared;
1324 : SlruWriteAllData fdata;
1325 16630 : int64 pageno = 0;
1326 16630 : int prevbank = SlotGetBankNumber(0);
1327 : bool ok;
1328 :
1329 : /* update the stats counter of flushes */
1330 16630 : pgstat_count_slru_flush(shared->slru_stats_idx);
1331 :
1332 : /*
1333 : * Find and write dirty pages
1334 : */
1335 16630 : fdata.num_files = 0;
1336 :
1337 16630 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1338 :
1339 404150 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1340 : {
1341 387520 : int curbank = SlotGetBankNumber(slotno);
1342 :
1343 : /*
1344 : * If the current bank lock is not same as the previous bank lock then
1345 : * release the previous lock and acquire the new lock.
1346 : */
1347 387520 : if (curbank != prevbank)
1348 : {
1349 7590 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1350 7590 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1351 7590 : prevbank = curbank;
1352 : }
1353 :
1354 : /* Do nothing if slot is unused */
1355 387520 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1356 376942 : continue;
1357 :
1358 10578 : SlruInternalWritePage(ctl, slotno, &fdata);
1359 :
1360 : /*
1361 : * In some places (e.g. checkpoints), we cannot assert that the slot
1362 : * is clean now, since another process might have re-dirtied it
1363 : * already. That's okay.
1364 : */
1365 : Assert(allow_redirtied ||
1366 : shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
1367 : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1368 : !shared->page_dirty[slotno]));
1369 : }
1370 :
1371 16630 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1372 :
1373 : /*
1374 : * Now close any files that were open
1375 : */
1376 16630 : ok = true;
1377 21314 : for (int i = 0; i < fdata.num_files; i++)
1378 : {
1379 4684 : if (CloseTransientFile(fdata.fd[i]) != 0)
1380 : {
1381 0 : slru_errcause = SLRU_CLOSE_FAILED;
1382 0 : slru_errno = errno;
1383 0 : pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT;
1384 0 : ok = false;
1385 : }
1386 : }
1387 16630 : if (!ok)
1388 0 : SlruReportIOError(ctl, pageno, InvalidTransactionId);
1389 :
1390 : /* Ensure that directory entries for new files are on disk. */
1391 16630 : if (ctl->sync_handler != SYNC_HANDLER_NONE)
1392 13312 : fsync_fname(ctl->Dir, true);
1393 16630 : }
1394 :
1395 : /*
1396 : * Remove all segments before the one holding the passed page number
1397 : *
1398 : * All SLRUs prevent concurrent calls to this function, either with an LWLock
1399 : * or by calling it only as part of a checkpoint. Mutual exclusion must begin
1400 : * before computing cutoffPage. Mutual exclusion must end after any limit
1401 : * update that would permit other backends to write fresh data into the
1402 : * segment immediately preceding the one containing cutoffPage. Otherwise,
1403 : * when the SLRU is quite full, SimpleLruTruncate() might delete that segment
1404 : * after it has accrued freshly-written data.
1405 : */
1406 : void
1407 3454 : SimpleLruTruncate(SlruCtl ctl, int64 cutoffPage)
1408 : {
1409 3454 : SlruShared shared = ctl->shared;
1410 : int prevbank;
1411 :
1412 : /* update the stats counter of truncates */
1413 3454 : pgstat_count_slru_truncate(shared->slru_stats_idx);
1414 :
1415 : /*
1416 : * Scan shared memory and remove any pages preceding the cutoff page, to
1417 : * ensure we won't rewrite them later. (Since this is normally called in
1418 : * or just after a checkpoint, any dirty pages should have been flushed
1419 : * already ... we're just being extra careful here.)
1420 : */
1421 3522 : restart:
1422 :
1423 : /*
1424 : * An important safety check: the current endpoint page must not be
1425 : * eligible for removal. This check is just a backstop against wraparound
1426 : * bugs elsewhere in SLRU handling, so we don't care if we read a slightly
1427 : * outdated value; therefore we don't add a memory barrier.
1428 : */
1429 3522 : if (ctl->PagePrecedes(pg_atomic_read_u64(&shared->latest_page_number),
1430 : cutoffPage))
1431 : {
1432 0 : ereport(LOG,
1433 : (errmsg("could not truncate directory \"%s\": apparent wraparound",
1434 : ctl->Dir)));
1435 0 : return;
1436 : }
1437 :
1438 3522 : prevbank = SlotGetBankNumber(0);
1439 3522 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1440 85438 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1441 : {
1442 81984 : int curbank = SlotGetBankNumber(slotno);
1443 :
1444 : /*
1445 : * If the current bank lock is not same as the previous bank lock then
1446 : * release the previous lock and acquire the new lock.
1447 : */
1448 81984 : if (curbank != prevbank)
1449 : {
1450 1636 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1451 1636 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1452 1636 : prevbank = curbank;
1453 : }
1454 :
1455 81984 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1456 72042 : continue;
1457 9942 : if (!ctl->PagePrecedes(shared->page_number[slotno], cutoffPage))
1458 9528 : continue;
1459 :
1460 : /*
1461 : * If page is clean, just change state to EMPTY (expected case).
1462 : */
1463 414 : if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1464 414 : !shared->page_dirty[slotno])
1465 : {
1466 346 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
1467 346 : continue;
1468 : }
1469 :
1470 : /*
1471 : * Hmm, we have (or may have) I/O operations acting on the page, so
1472 : * we've got to wait for them to finish and then start again. This is
1473 : * the same logic as in SlruSelectLRUPage. (XXX if page is dirty,
1474 : * wouldn't it be OK to just discard it without writing it?
1475 : * SlruMayDeleteSegment() uses a stricter qualification, so we might
1476 : * not delete this page in the end; even if we don't delete it, we
1477 : * won't have cause to read its data again. For now, keep the logic
1478 : * the same as it was.)
1479 : */
1480 68 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1481 68 : SlruInternalWritePage(ctl, slotno, NULL);
1482 : else
1483 0 : SimpleLruWaitIO(ctl, slotno);
1484 :
1485 68 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1486 68 : goto restart;
1487 : }
1488 :
1489 3454 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1490 :
1491 : /* Now we can remove the old segment(s) */
1492 3454 : (void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage);
1493 : }
1494 :
1495 : /*
1496 : * Delete an individual SLRU segment.
1497 : *
1498 : * NB: This does not touch the SLRU buffers themselves, callers have to ensure
1499 : * they either can't yet contain anything, or have already been cleaned out.
1500 : */
1501 : static void
1502 239928 : SlruInternalDeleteSegment(SlruCtl ctl, int64 segno)
1503 : {
1504 : char path[MAXPGPATH];
1505 :
1506 : /* Forget any fsync requests queued for this segment. */
1507 239928 : if (ctl->sync_handler != SYNC_HANDLER_NONE)
1508 : {
1509 : FileTag tag;
1510 :
1511 26544 : INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
1512 26544 : RegisterSyncRequest(&tag, SYNC_FORGET_REQUEST, true);
1513 : }
1514 :
1515 : /* Unlink the file. */
1516 239928 : SlruFileName(ctl, path, segno);
1517 239928 : ereport(DEBUG2, (errmsg_internal("removing file \"%s\"", path)));
1518 239928 : unlink(path);
1519 239928 : }
1520 :
1521 : /*
1522 : * Delete an individual SLRU segment, identified by the segment number.
1523 : */
1524 : void
1525 4 : SlruDeleteSegment(SlruCtl ctl, int64 segno)
1526 : {
1527 4 : SlruShared shared = ctl->shared;
1528 4 : int prevbank = SlotGetBankNumber(0);
1529 : bool did_write;
1530 :
1531 : /* Clean out any possibly existing references to the segment. */
1532 4 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1533 4 : restart:
1534 4 : did_write = false;
1535 68 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1536 : {
1537 : int64 pagesegno;
1538 64 : int curbank = SlotGetBankNumber(slotno);
1539 :
1540 : /*
1541 : * If the current bank lock is not same as the previous bank lock then
1542 : * release the previous lock and acquire the new lock.
1543 : */
1544 64 : if (curbank != prevbank)
1545 : {
1546 0 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1547 0 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1548 0 : prevbank = curbank;
1549 : }
1550 :
1551 64 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1552 0 : continue;
1553 :
1554 64 : pagesegno = shared->page_number[slotno] / SLRU_PAGES_PER_SEGMENT;
1555 : /* not the segment we're looking for */
1556 64 : if (pagesegno != segno)
1557 14 : continue;
1558 :
1559 : /* If page is clean, just change state to EMPTY (expected case). */
1560 50 : if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1561 50 : !shared->page_dirty[slotno])
1562 : {
1563 50 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
1564 50 : continue;
1565 : }
1566 :
1567 : /* Same logic as SimpleLruTruncate() */
1568 0 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1569 0 : SlruInternalWritePage(ctl, slotno, NULL);
1570 : else
1571 0 : SimpleLruWaitIO(ctl, slotno);
1572 :
1573 0 : did_write = true;
1574 : }
1575 :
1576 : /*
1577 : * Be extra careful and re-check. The IO functions release the control
1578 : * lock, so new pages could have been read in.
1579 : */
1580 4 : if (did_write)
1581 0 : goto restart;
1582 :
1583 4 : SlruInternalDeleteSegment(ctl, segno);
1584 :
1585 4 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1586 4 : }
1587 :
1588 : /*
1589 : * Determine whether a segment is okay to delete.
1590 : *
1591 : * segpage is the first page of the segment, and cutoffPage is the oldest (in
1592 : * PagePrecedes order) page in the SLRU containing still-useful data. Since
1593 : * every core PagePrecedes callback implements "wrap around", check the
1594 : * segment's first and last pages:
1595 : *
1596 : * first<cutoff && last<cutoff: yes
1597 : * first<cutoff && last>=cutoff: no; cutoff falls inside this segment
1598 : * first>=cutoff && last<cutoff: no; wrap point falls inside this segment
1599 : * first>=cutoff && last>=cutoff: no; every page of this segment is too young
1600 : */
1601 : static bool
1602 1106588 : SlruMayDeleteSegment(SlruCtl ctl, int64 segpage, int64 cutoffPage)
1603 : {
1604 1106588 : int64 seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
1605 :
1606 : Assert(segpage % SLRU_PAGES_PER_SEGMENT == 0);
1607 :
1608 1347824 : return (ctl->PagePrecedes(segpage, cutoffPage) &&
1609 241236 : ctl->PagePrecedes(seg_last_page, cutoffPage));
1610 : }
1611 :
1612 : #ifdef USE_ASSERT_CHECKING
1613 : static void
1614 : SlruPagePrecedesTestOffset(SlruCtl ctl, int per_page, uint32 offset)
1615 : {
1616 : TransactionId lhs,
1617 : rhs;
1618 : int64 newestPage,
1619 : oldestPage;
1620 : TransactionId newestXact,
1621 : oldestXact;
1622 :
1623 : /*
1624 : * Compare an XID pair having undefined order (see RFC 1982), a pair at
1625 : * "opposite ends" of the XID space. TransactionIdPrecedes() treats each
1626 : * as preceding the other. If RHS is oldestXact, LHS is the first XID we
1627 : * must not assign.
1628 : */
1629 : lhs = per_page + offset; /* skip first page to avoid non-normal XIDs */
1630 : rhs = lhs + (1U << 31);
1631 : Assert(TransactionIdPrecedes(lhs, rhs));
1632 : Assert(TransactionIdPrecedes(rhs, lhs));
1633 : Assert(!TransactionIdPrecedes(lhs - 1, rhs));
1634 : Assert(TransactionIdPrecedes(rhs, lhs - 1));
1635 : Assert(TransactionIdPrecedes(lhs + 1, rhs));
1636 : Assert(!TransactionIdPrecedes(rhs, lhs + 1));
1637 : Assert(!TransactionIdFollowsOrEquals(lhs, rhs));
1638 : Assert(!TransactionIdFollowsOrEquals(rhs, lhs));
1639 : Assert(!ctl->PagePrecedes(lhs / per_page, lhs / per_page));
1640 : Assert(!ctl->PagePrecedes(lhs / per_page, rhs / per_page));
1641 : Assert(!ctl->PagePrecedes(rhs / per_page, lhs / per_page));
1642 : Assert(!ctl->PagePrecedes((lhs - per_page) / per_page, rhs / per_page));
1643 : Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 3 * per_page) / per_page));
1644 : Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 2 * per_page) / per_page));
1645 : Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 1 * per_page) / per_page)
1646 : || (1U << 31) % per_page != 0); /* See CommitTsPagePrecedes() */
1647 : Assert(ctl->PagePrecedes((lhs + 1 * per_page) / per_page, rhs / per_page)
1648 : || (1U << 31) % per_page != 0);
1649 : Assert(ctl->PagePrecedes((lhs + 2 * per_page) / per_page, rhs / per_page));
1650 : Assert(ctl->PagePrecedes((lhs + 3 * per_page) / per_page, rhs / per_page));
1651 : Assert(!ctl->PagePrecedes(rhs / per_page, (lhs + per_page) / per_page));
1652 :
1653 : /*
1654 : * GetNewTransactionId() has assigned the last XID it can safely use, and
1655 : * that XID is in the *LAST* page of the second segment. We must not
1656 : * delete that segment.
1657 : */
1658 : newestPage = 2 * SLRU_PAGES_PER_SEGMENT - 1;
1659 : newestXact = newestPage * per_page + offset;
1660 : Assert(newestXact / per_page == newestPage);
1661 : oldestXact = newestXact + 1;
1662 : oldestXact -= 1U << 31;
1663 : oldestPage = oldestXact / per_page;
1664 : Assert(!SlruMayDeleteSegment(ctl,
1665 : (newestPage -
1666 : newestPage % SLRU_PAGES_PER_SEGMENT),
1667 : oldestPage));
1668 :
1669 : /*
1670 : * GetNewTransactionId() has assigned the last XID it can safely use, and
1671 : * that XID is in the *FIRST* page of the second segment. We must not
1672 : * delete that segment.
1673 : */
1674 : newestPage = SLRU_PAGES_PER_SEGMENT;
1675 : newestXact = newestPage * per_page + offset;
1676 : Assert(newestXact / per_page == newestPage);
1677 : oldestXact = newestXact + 1;
1678 : oldestXact -= 1U << 31;
1679 : oldestPage = oldestXact / per_page;
1680 : Assert(!SlruMayDeleteSegment(ctl,
1681 : (newestPage -
1682 : newestPage % SLRU_PAGES_PER_SEGMENT),
1683 : oldestPage));
1684 : }
1685 :
1686 : /*
1687 : * Unit-test a PagePrecedes function.
1688 : *
1689 : * This assumes every uint32 >= FirstNormalTransactionId is a valid key. It
1690 : * assumes each value occupies a contiguous, fixed-size region of SLRU bytes.
1691 : * (MultiXactMemberCtl separates flags from XIDs. NotifyCtl has
1692 : * variable-length entries, no keys, and no random access. These unit tests
1693 : * do not apply to them.)
1694 : */
1695 : void
1696 : SlruPagePrecedesUnitTests(SlruCtl ctl, int per_page)
1697 : {
1698 : /* Test first, middle and last entries of a page. */
1699 : SlruPagePrecedesTestOffset(ctl, per_page, 0);
1700 : SlruPagePrecedesTestOffset(ctl, per_page, per_page / 2);
1701 : SlruPagePrecedesTestOffset(ctl, per_page, per_page - 1);
1702 : }
1703 : #endif
1704 :
1705 : /*
1706 : * SlruScanDirectory callback
1707 : * This callback reports true if there's any segment wholly prior to the
1708 : * one containing the page passed as "data".
1709 : */
1710 : bool
1711 731446 : SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int64 segpage,
1712 : void *data)
1713 : {
1714 731446 : int64 cutoffPage = *(int64 *) data;
1715 :
1716 731446 : if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
1717 194 : return true; /* found one; don't iterate any more */
1718 :
1719 731252 : return false; /* keep going */
1720 : }
1721 :
1722 : /*
1723 : * SlruScanDirectory callback.
1724 : * This callback deletes segments prior to the one passed in as "data".
1725 : */
1726 : static bool
1727 375142 : SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int64 segpage,
1728 : void *data)
1729 : {
1730 375142 : int64 cutoffPage = *(int64 *) data;
1731 :
1732 375142 : if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
1733 239908 : SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
1734 :
1735 375142 : return false; /* keep going */
1736 : }
1737 :
1738 : /*
1739 : * SlruScanDirectory callback.
1740 : * This callback deletes all segments.
1741 : */
1742 : bool
1743 16 : SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int64 segpage, void *data)
1744 : {
1745 16 : SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
1746 :
1747 16 : return false; /* keep going */
1748 : }
1749 :
1750 : /*
1751 : * An internal function used by SlruScanDirectory().
1752 : *
1753 : * Returns true if a file with a name of a given length may be a correct
1754 : * SLRU segment.
1755 : */
1756 : static inline bool
1757 1125868 : SlruCorrectSegmentFilenameLength(SlruCtl ctl, size_t len)
1758 : {
1759 1125868 : if (ctl->long_segment_names)
1760 4216 : return (len == 15); /* see SlruFileName() */
1761 : else
1762 :
1763 : /*
1764 : * Commit 638cf09e76d allowed 5-character lengths. Later commit
1765 : * 73c986adde5 allowed 6-character length.
1766 : *
1767 : * Note: There is an ongoing plan to migrate all SLRUs to 64-bit page
1768 : * numbers, and the corresponding 15-character file names, which may
1769 : * eventually deprecate the support for 4, 5, and 6-character names.
1770 : */
1771 1121652 : return (len == 4 || len == 5 || len == 6);
1772 : }
1773 :
1774 : /*
1775 : * Scan the SimpleLru directory and apply a callback to each file found in it.
1776 : *
1777 : * If the callback returns true, the scan is stopped. The last return value
1778 : * from the callback is returned.
1779 : *
1780 : * The callback receives the following arguments: 1. the SlruCtl struct for the
1781 : * slru being truncated; 2. the filename being considered; 3. the page number
1782 : * for the first page of that file; 4. a pointer to the opaque data given to us
1783 : * by the caller.
1784 : *
1785 : * Note that the ordering in which the directory is scanned is not guaranteed.
1786 : *
1787 : * Note that no locking is applied.
1788 : */
1789 : bool
1790 9632 : SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)
1791 : {
1792 9632 : bool retval = false;
1793 : DIR *cldir;
1794 : struct dirent *clde;
1795 : int64 segno;
1796 : int64 segpage;
1797 :
1798 9632 : cldir = AllocateDir(ctl->Dir);
1799 1135306 : while ((clde = ReadDir(cldir, ctl->Dir)) != NULL)
1800 : {
1801 : size_t len;
1802 :
1803 1125868 : len = strlen(clde->d_name);
1804 :
1805 1125868 : if (SlruCorrectSegmentFilenameLength(ctl, len) &&
1806 1106604 : strspn(clde->d_name, "0123456789ABCDEF") == len)
1807 : {
1808 1106604 : segno = strtoi64(clde->d_name, NULL, 16);
1809 1106604 : segpage = segno * SLRU_PAGES_PER_SEGMENT;
1810 :
1811 1106604 : elog(DEBUG2, "SlruScanDirectory invoking callback on %s/%s",
1812 : ctl->Dir, clde->d_name);
1813 1106604 : retval = callback(ctl, clde->d_name, segpage, data);
1814 1106604 : if (retval)
1815 194 : break;
1816 : }
1817 : }
1818 9632 : FreeDir(cldir);
1819 :
1820 9632 : return retval;
1821 : }
1822 :
1823 : /*
1824 : * Individual SLRUs (clog, ...) have to provide a sync.c handler function so
1825 : * that they can provide the correct "SlruCtl" (otherwise we don't know how to
1826 : * build the path), but they just forward to this common implementation that
1827 : * performs the fsync.
1828 : */
1829 : int
1830 4 : SlruSyncFileTag(SlruCtl ctl, const FileTag *ftag, char *path)
1831 : {
1832 : int fd;
1833 : int save_errno;
1834 : int result;
1835 :
1836 4 : SlruFileName(ctl, path, ftag->segno);
1837 :
1838 4 : fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
1839 4 : if (fd < 0)
1840 0 : return -1;
1841 :
1842 4 : pgstat_report_wait_start(WAIT_EVENT_SLRU_FLUSH_SYNC);
1843 4 : result = pg_fsync(fd);
1844 4 : pgstat_report_wait_end();
1845 4 : save_errno = errno;
1846 :
1847 4 : CloseTransientFile(fd);
1848 :
1849 4 : errno = save_errno;
1850 4 : return result;
1851 : }
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