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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 "storage/shmem_internal.h"
74 : : #include "utils/guc.h"
75 : : #include "utils/memutils.h"
76 : : #include "utils/wait_event.h"
77 : :
78 : : /*
79 : : * Converts segment number to the filename of the segment.
80 : : *
81 : : * "path" should point to a buffer at least MAXPGPATH characters long.
82 : : *
83 : : * If ctl->long_segment_names is true, segno can be in the range [0, 2^60-1].
84 : : * The resulting file name is made of 15 characters, e.g. dir/123456789ABCDEF.
85 : : *
86 : : * If ctl->long_segment_names is false, segno can be in the range [0, 2^24-1].
87 : : * The resulting file name is made of 4 to 6 characters, as of:
88 : : *
89 : : * dir/1234 for [0, 2^16-1]
90 : : * dir/12345 for [2^16, 2^20-1]
91 : : * dir/123456 for [2^20, 2^24-1]
92 : : */
93 : : static inline int
94 : 7506222 : SlruFileName(SlruDesc *ctl, char *path, int64 segno)
95 : : {
96 [ + + ]: 7506222 : if (ctl->options.long_segment_names)
97 : : {
98 : : /*
99 : : * We could use 16 characters here but the disadvantage would be that
100 : : * the SLRU segments will be hard to distinguish from WAL segments.
101 : : *
102 : : * For this reason we use 15 characters. It is enough but also means
103 : : * that in the future we can't decrease SLRU_PAGES_PER_SEGMENT easily.
104 : : */
105 : : Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFFFFFFFFFFF));
106 : 16622 : return snprintf(path, MAXPGPATH, "%s/%015" PRIX64, ctl->options.Dir, segno);
107 : : }
108 : : else
109 : : {
110 : : /*
111 : : * Despite the fact that %04X format string is used up to 24 bit
112 : : * integers are allowed. See SlruCorrectSegmentFilenameLength()
113 : : */
114 : : Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFF));
115 : 7489600 : return snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->options.Dir,
116 : : (unsigned int) segno);
117 : : }
118 : : }
119 : :
120 : : /*
121 : : * During SimpleLruWriteAll(), we will usually not need to write more than one
122 : : * or two physical files, but we may need to write several pages per file. We
123 : : * can consolidate the I/O requests by leaving files open until control returns
124 : : * to SimpleLruWriteAll(). This data structure remembers which files are open.
125 : : */
126 : : #define MAX_WRITEALL_BUFFERS 16
127 : :
128 : : typedef struct SlruWriteAllData
129 : : {
130 : : int num_files; /* # files actually open */
131 : : int fd[MAX_WRITEALL_BUFFERS]; /* their FD's */
132 : : int64 segno[MAX_WRITEALL_BUFFERS]; /* their log seg#s */
133 : : } SlruWriteAllData;
134 : :
135 : : typedef struct SlruWriteAllData *SlruWriteAll;
136 : :
137 : :
138 : : /*
139 : : * Bank size for the slot array. Pages are assigned a bank according to their
140 : : * page number, with each bank being this size. We want a power of 2 so that
141 : : * we can determine the bank number for a page with just bit shifting; we also
142 : : * want to keep the bank size small so that LRU victim search is fast. 16
143 : : * buffers per bank seems a good number.
144 : : */
145 : : #define SLRU_BANK_BITSHIFT 4
146 : : #define SLRU_BANK_SIZE (1 << SLRU_BANK_BITSHIFT)
147 : :
148 : : /*
149 : : * Macro to get the bank number to which the slot belongs.
150 : : */
151 : : #define SlotGetBankNumber(slotno) ((slotno) >> SLRU_BANK_BITSHIFT)
152 : :
153 : :
154 : : /*
155 : : * Populate a file tag describing a segment file. We only use the segment
156 : : * number, since we can derive everything else we need by having separate
157 : : * sync handler functions for clog, multixact etc.
158 : : */
159 : : #define INIT_SLRUFILETAG(a,xx_handler,xx_segno) \
160 : : ( \
161 : : memset(&(a), 0, sizeof(FileTag)), \
162 : : (a).handler = (xx_handler), \
163 : : (a).segno = (xx_segno) \
164 : : )
165 : :
166 : : /* Saved info for SlruReportIOError */
167 : : typedef enum
168 : : {
169 : : SLRU_OPEN_FAILED,
170 : : SLRU_SEEK_FAILED,
171 : : SLRU_READ_FAILED,
172 : : SLRU_WRITE_FAILED,
173 : : SLRU_FSYNC_FAILED,
174 : : SLRU_CLOSE_FAILED,
175 : : } SlruErrorCause;
176 : :
177 : : static SlruErrorCause slru_errcause;
178 : : static int slru_errno;
179 : :
180 : :
181 : : static void SimpleLruZeroLSNs(SlruDesc *ctl, int slotno);
182 : : static void SimpleLruWaitIO(SlruDesc *ctl, int slotno);
183 : : static void SlruInternalWritePage(SlruDesc *ctl, int slotno, SlruWriteAll fdata);
184 : : static bool SlruPhysicalReadPage(SlruDesc *ctl, int64 pageno, int slotno);
185 : : static bool SlruPhysicalWritePage(SlruDesc *ctl, int64 pageno, int slotno,
186 : : SlruWriteAll fdata);
187 : : static void SlruReportIOError(SlruDesc *ctl, int64 pageno,
188 : : const void *opaque_data);
189 : : static int SlruSelectLRUPage(SlruDesc *ctl, int64 pageno);
190 : :
191 : : static bool SlruScanDirCbDeleteCutoff(SlruDesc *ctl, char *filename,
192 : : int64 segpage, void *data);
193 : : static void SlruInternalDeleteSegment(SlruDesc *ctl, int64 segno);
194 : : static inline void SlruRecentlyUsed(SlruShared shared, int slotno);
195 : :
196 : :
197 : : /*
198 : : * Initialization of shared memory
199 : : */
200 : :
201 : : static Size
202 : 8747 : SimpleLruShmemSize(int nslots, int nlsns)
203 : : {
204 : 8747 : int nbanks = nslots / SLRU_BANK_SIZE;
205 : : Size sz;
206 : :
207 : : Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
208 : : Assert(nslots % SLRU_BANK_SIZE == 0);
209 : :
210 : : /* we assume nslots isn't so large as to risk overflow */
211 : 8747 : sz = MAXALIGN(sizeof(SlruSharedData));
212 : 8747 : sz += MAXALIGN(nslots * sizeof(char *)); /* page_buffer[] */
213 : 8747 : sz += MAXALIGN(nslots * sizeof(SlruPageStatus)); /* page_status[] */
214 : 8747 : sz += MAXALIGN(nslots * sizeof(bool)); /* page_dirty[] */
215 : 8747 : sz += MAXALIGN(nslots * sizeof(int64)); /* page_number[] */
216 : 8747 : sz += MAXALIGN(nslots * sizeof(int)); /* page_lru_count[] */
217 : 8747 : sz += MAXALIGN(nslots * sizeof(LWLockPadded)); /* buffer_locks[] */
218 : 8747 : sz += MAXALIGN(nbanks * sizeof(LWLockPadded)); /* bank_locks[] */
219 : 8747 : sz += MAXALIGN(nbanks * sizeof(int)); /* bank_cur_lru_count[] */
220 : :
221 [ + + ]: 8747 : if (nlsns > 0)
222 : 1249 : sz += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr)); /* group_lsn[] */
223 : :
224 : 8747 : return BUFFERALIGN(sz) + BLCKSZ * nslots;
225 : : }
226 : :
227 : : /*
228 : : * Determine a number of SLRU buffers to use.
229 : : *
230 : : * We simply divide shared_buffers by the divisor given and cap
231 : : * that at the maximum given; but always at least SLRU_BANK_SIZE.
232 : : * Round down to the nearest multiple of SLRU_BANK_SIZE.
233 : : */
234 : : int
235 : 3725 : SimpleLruAutotuneBuffers(int divisor, int max)
236 : : {
237 : 3725 : return Min(max - (max % SLRU_BANK_SIZE),
238 : : Max(SLRU_BANK_SIZE,
239 : : NBuffers / divisor - (NBuffers / divisor) % SLRU_BANK_SIZE));
240 : : }
241 : :
242 : : /*
243 : : * Register a simple LRU cache in shared memory.
244 : : */
245 : : void
246 : 8747 : SimpleLruRequestWithOpts(const SlruOpts *options)
247 : : {
248 : : SlruOpts *options_copy;
249 : :
250 : : Assert(options->name != NULL);
251 : : Assert(options->nslots > 0);
252 : : Assert(options->PagePrecedes != NULL);
253 : : Assert(options->errdetail_for_io_error != NULL);
254 : :
255 : 8747 : options_copy = MemoryContextAlloc(TopMemoryContext,
256 : : sizeof(SlruOpts));
257 : 8747 : memcpy(options_copy, options, sizeof(SlruOpts));
258 : :
259 : 8747 : options_copy->base.name = options->name;
260 : 8747 : options_copy->base.size = SimpleLruShmemSize(options_copy->nslots, options_copy->nlsns);
261 : :
262 : 8747 : ShmemRequestInternal(&options_copy->base, SHMEM_KIND_SLRU);
263 : 8747 : }
264 : :
265 : : /* Initialize locks and shared memory area */
266 : : void
267 : 8726 : shmem_slru_init(void *location, ShmemStructOpts *base_options)
268 : : {
269 : 8726 : SlruOpts *options = (SlruOpts *) base_options;
270 : 8726 : SlruDesc *desc = (SlruDesc *) options->desc;
271 : : char namebuf[NAMEDATALEN];
272 : : SlruShared shared;
273 : 8726 : int nslots = options->nslots;
274 : 8726 : int nbanks = nslots / SLRU_BANK_SIZE;
275 : 8726 : int nlsns = options->nlsns;
276 : : char *ptr;
277 : : Size offset;
278 : :
279 : 8726 : shared = (SlruShared) location;
280 : 8726 : desc->shared = shared;
281 : 8726 : desc->nbanks = nbanks;
282 : 8726 : memcpy(&desc->options, options, sizeof(SlruOpts));
283 : :
284 : : /* assign new tranche IDs, if not given */
285 [ + + ]: 8726 : if (desc->options.buffer_tranche_id == 0)
286 : : {
287 : 4 : snprintf(namebuf, sizeof(namebuf), "%s buffer", desc->options.name);
288 : 4 : desc->options.buffer_tranche_id = LWLockNewTrancheId(namebuf);
289 : : }
290 [ + + ]: 8726 : if (desc->options.bank_tranche_id == 0)
291 : : {
292 : 4 : snprintf(namebuf, sizeof(namebuf), "%s bank", desc->options.name);
293 : 4 : desc->options.bank_tranche_id = LWLockNewTrancheId(namebuf);
294 : : }
295 : :
296 : : Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
297 : :
298 : 8726 : memset(shared, 0, sizeof(SlruSharedData));
299 : :
300 : 8726 : shared->num_slots = nslots;
301 : 8726 : shared->lsn_groups_per_page = nlsns;
302 : :
303 : 8726 : pg_atomic_init_u64(&shared->latest_page_number, 0);
304 : :
305 : 8726 : shared->slru_stats_idx = pgstat_get_slru_index(desc->options.name);
306 : :
307 : 8726 : ptr = (char *) shared;
308 : 8726 : offset = MAXALIGN(sizeof(SlruSharedData));
309 : 8726 : shared->page_buffer = (char **) (ptr + offset);
310 : 8726 : offset += MAXALIGN(nslots * sizeof(char *));
311 : 8726 : shared->page_status = (SlruPageStatus *) (ptr + offset);
312 : 8726 : offset += MAXALIGN(nslots * sizeof(SlruPageStatus));
313 : 8726 : shared->page_dirty = (bool *) (ptr + offset);
314 : 8726 : offset += MAXALIGN(nslots * sizeof(bool));
315 : 8726 : shared->page_number = (int64 *) (ptr + offset);
316 : 8726 : offset += MAXALIGN(nslots * sizeof(int64));
317 : 8726 : shared->page_lru_count = (int *) (ptr + offset);
318 : 8726 : offset += MAXALIGN(nslots * sizeof(int));
319 : :
320 : : /* Initialize LWLocks */
321 : 8726 : shared->buffer_locks = (LWLockPadded *) (ptr + offset);
322 : 8726 : offset += MAXALIGN(nslots * sizeof(LWLockPadded));
323 : 8726 : shared->bank_locks = (LWLockPadded *) (ptr + offset);
324 : 8726 : offset += MAXALIGN(nbanks * sizeof(LWLockPadded));
325 : 8726 : shared->bank_cur_lru_count = (int *) (ptr + offset);
326 : 8726 : offset += MAXALIGN(nbanks * sizeof(int));
327 : :
328 [ + + ]: 8726 : if (nlsns > 0)
329 : : {
330 : 1246 : shared->group_lsn = (XLogRecPtr *) (ptr + offset);
331 : 1246 : offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));
332 : : }
333 : :
334 : 8726 : ptr += BUFFERALIGN(offset);
335 [ + + ]: 222502 : for (int slotno = 0; slotno < nslots; slotno++)
336 : : {
337 : 213776 : LWLockInitialize(&shared->buffer_locks[slotno].lock,
338 : : desc->options.buffer_tranche_id);
339 : :
340 : 213776 : shared->page_buffer[slotno] = ptr;
341 : 213776 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
342 : 213776 : shared->page_dirty[slotno] = false;
343 : 213776 : shared->page_lru_count[slotno] = 0;
344 : 213776 : ptr += BLCKSZ;
345 : : }
346 : :
347 : : /* Initialize the slot banks. */
348 [ + + ]: 22087 : for (int bankno = 0; bankno < nbanks; bankno++)
349 : : {
350 : 13361 : LWLockInitialize(&shared->bank_locks[bankno].lock, desc->options.bank_tranche_id);
351 : 13361 : shared->bank_cur_lru_count[bankno] = 0;
352 : : }
353 : :
354 : : /* Should fit to estimated shmem size */
355 : : Assert(ptr - (char *) shared <= SimpleLruShmemSize(nslots, nlsns));
356 : 8726 : }
357 : :
358 : : void
359 : 0 : shmem_slru_attach(void *location, ShmemStructOpts *base_options)
360 : : {
361 : 0 : SlruOpts *options = (SlruOpts *) base_options;
362 : 0 : SlruDesc *desc = (SlruDesc *) options->desc;
363 : 0 : int nslots = options->nslots;
364 : 0 : int nbanks = nslots / SLRU_BANK_SIZE;
365 : :
366 : 0 : desc->shared = (SlruShared) location;
367 : 0 : desc->nbanks = nbanks;
368 : 0 : memcpy(&desc->options, options, sizeof(SlruOpts));
369 : 0 : }
370 : :
371 : :
372 : : /*
373 : : * Helper function for GUC check_hook to check whether slru buffers are in
374 : : * multiples of SLRU_BANK_SIZE.
375 : : */
376 : : bool
377 : 12778 : check_slru_buffers(const char *name, int *newval)
378 : : {
379 : : /* Valid values are multiples of SLRU_BANK_SIZE */
380 [ + - ]: 12778 : if (*newval % SLRU_BANK_SIZE == 0)
381 : 12778 : return true;
382 : :
383 : 0 : GUC_check_errdetail("\"%s\" must be a multiple of %d.", name,
384 : : SLRU_BANK_SIZE);
385 : 0 : return false;
386 : : }
387 : :
388 : : /*
389 : : * Initialize (or reinitialize) a page to zeroes.
390 : : *
391 : : * The page is not actually written, just set up in shared memory.
392 : : * The slot number of the new page is returned.
393 : : *
394 : : * Bank lock must be held at entry, and will be held at exit.
395 : : */
396 : : int
397 : 7346033 : SimpleLruZeroPage(SlruDesc *ctl, int64 pageno)
398 : : {
399 : 7346033 : SlruShared shared = ctl->shared;
400 : : int slotno;
401 : :
402 : : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
403 : :
404 : : /* Find a suitable buffer slot for the page */
405 : 7346033 : slotno = SlruSelectLRUPage(ctl, pageno);
406 : : Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
407 : : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
408 : : !shared->page_dirty[slotno]) ||
409 : : shared->page_number[slotno] == pageno);
410 : :
411 : : /* Mark the slot as containing this page */
412 : 7346033 : shared->page_number[slotno] = pageno;
413 : 7346033 : shared->page_status[slotno] = SLRU_PAGE_VALID;
414 : 7346033 : shared->page_dirty[slotno] = true;
415 : 7346033 : SlruRecentlyUsed(shared, slotno);
416 : :
417 : : /* Set the buffer to zeroes */
418 [ + - + - : 7346033 : MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
+ - - + -
- ]
419 : :
420 : : /* Set the LSNs for this new page to zero */
421 : 7346033 : SimpleLruZeroLSNs(ctl, slotno);
422 : :
423 : : /*
424 : : * Assume this page is now the latest active page.
425 : : *
426 : : * Note that because both this routine and SlruSelectLRUPage run with a
427 : : * SLRU bank lock held, it is not possible for this to be zeroing a page
428 : : * that SlruSelectLRUPage is going to evict simultaneously. Therefore,
429 : : * there's no memory barrier here.
430 : : */
431 : 7346033 : pg_atomic_write_u64(&shared->latest_page_number, pageno);
432 : :
433 : : /* update the stats counter of zeroed pages */
434 : 7346033 : pgstat_count_slru_blocks_zeroed(shared->slru_stats_idx);
435 : :
436 : 7346033 : return slotno;
437 : : }
438 : :
439 : : /*
440 : : * Zero all the LSNs we store for this slru page.
441 : : *
442 : : * This should be called each time we create a new page, and each time we read
443 : : * in a page from disk into an existing buffer. (Such an old page cannot
444 : : * have any interesting LSNs, since we'd have flushed them before writing
445 : : * the page in the first place.)
446 : : *
447 : : * This assumes that InvalidXLogRecPtr is bitwise-all-0.
448 : : */
449 : : static void
450 : 7363678 : SimpleLruZeroLSNs(SlruDesc *ctl, int slotno)
451 : : {
452 : 7363678 : SlruShared shared = ctl->shared;
453 : :
454 [ + + ]: 7363678 : if (shared->lsn_groups_per_page > 0)
455 [ + - + - : 433316 : MemSet(&shared->group_lsn[slotno * shared->lsn_groups_per_page], 0,
+ - - + -
- ]
456 : : shared->lsn_groups_per_page * sizeof(XLogRecPtr));
457 : 7363678 : }
458 : :
459 : : /*
460 : : * This is a convenience wrapper for the common case of zeroing a page and
461 : : * immediately flushing it to disk.
462 : : *
463 : : * SLRU bank lock is acquired and released here.
464 : : */
465 : : void
466 : 242 : SimpleLruZeroAndWritePage(SlruDesc *ctl, int64 pageno)
467 : : {
468 : : int slotno;
469 : : LWLock *lock;
470 : :
471 : 242 : lock = SimpleLruGetBankLock(ctl, pageno);
472 : 242 : LWLockAcquire(lock, LW_EXCLUSIVE);
473 : :
474 : : /* Create and zero the page */
475 : 242 : slotno = SimpleLruZeroPage(ctl, pageno);
476 : :
477 : : /* Make sure it's written out */
478 : 242 : SimpleLruWritePage(ctl, slotno);
479 : : Assert(!ctl->shared->page_dirty[slotno]);
480 : :
481 : 242 : LWLockRelease(lock);
482 : 242 : }
483 : :
484 : : /*
485 : : * Wait for any active I/O on a page slot to finish. (This does not
486 : : * guarantee that new I/O hasn't been started before we return, though.
487 : : * In fact the slot might not even contain the same page anymore.)
488 : : *
489 : : * Bank lock must be held at entry, and will be held at exit.
490 : : */
491 : : static void
492 : 1 : SimpleLruWaitIO(SlruDesc *ctl, int slotno)
493 : : {
494 : 1 : SlruShared shared = ctl->shared;
495 : 1 : int bankno = SlotGetBankNumber(slotno);
496 : :
497 : : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
498 : :
499 : : /* See notes at top of file */
500 : 1 : LWLockRelease(&shared->bank_locks[bankno].lock);
501 : 1 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED);
502 : 1 : LWLockRelease(&shared->buffer_locks[slotno].lock);
503 : 1 : LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
504 : :
505 : : /*
506 : : * If the slot is still in an io-in-progress state, then either someone
507 : : * already started a new I/O on the slot, or a previous I/O failed and
508 : : * neglected to reset the page state. That shouldn't happen, really, but
509 : : * it seems worth a few extra cycles to check and recover from it. We can
510 : : * cheaply test for failure by seeing if the buffer lock is still held (we
511 : : * assume that transaction abort would release the lock).
512 : : */
513 [ + - ]: 1 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
514 [ - + ]: 1 : shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS)
515 : : {
516 [ # # ]: 0 : if (LWLockConditionalAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED))
517 : : {
518 : : /* indeed, the I/O must have failed */
519 [ # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS)
520 : 0 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
521 : : else /* write_in_progress */
522 : : {
523 : 0 : shared->page_status[slotno] = SLRU_PAGE_VALID;
524 : 0 : shared->page_dirty[slotno] = true;
525 : : }
526 : 0 : LWLockRelease(&shared->buffer_locks[slotno].lock);
527 : : }
528 : : }
529 : 1 : }
530 : :
531 : : /*
532 : : * Find a page in a shared buffer, reading it in if necessary.
533 : : * The page number must correspond to an already-initialized page.
534 : : *
535 : : * If write_ok is true then it is OK to return a page that is in
536 : : * WRITE_IN_PROGRESS state; it is the caller's responsibility to be sure
537 : : * that modification of the page is safe. If write_ok is false then we
538 : : * will not return the page until it is not undergoing active I/O.
539 : : *
540 : : * On error, the passed-in 'opaque_data' is passed to the
541 : : * 'errdetail_for_io_error' callback, to provide details on the operation that
542 : : * failed. It is only used for error reporting.
543 : : *
544 : : * Return value is the shared-buffer slot number now holding the page.
545 : : * The buffer's LRU access info is updated.
546 : : *
547 : : * The correct bank lock must be held at entry, and will be held at exit.
548 : : */
549 : : int
550 : 398695 : SimpleLruReadPage(SlruDesc *ctl, int64 pageno, bool write_ok,
551 : : const void *opaque_data)
552 : : {
553 : 398695 : SlruShared shared = ctl->shared;
554 : 398695 : LWLock *banklock = SimpleLruGetBankLock(ctl, pageno);
555 : :
556 : : Assert(LWLockHeldByMeInMode(banklock, LW_EXCLUSIVE));
557 : :
558 : : /* Outer loop handles restart if we must wait for someone else's I/O */
559 : : for (;;)
560 : 1 : {
561 : : int slotno;
562 : : bool ok;
563 : :
564 : : /* See if page already is in memory; if not, pick victim slot */
565 : 398696 : slotno = SlruSelectLRUPage(ctl, pageno);
566 : :
567 : : /* Did we find the page in memory? */
568 [ + + ]: 398696 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
569 [ + + ]: 397554 : shared->page_number[slotno] == pageno)
570 : : {
571 : : /*
572 : : * If page is still being read in, we must wait for I/O. Likewise
573 : : * if the page is being written and the caller said that's not OK.
574 : : */
575 [ + - ]: 381051 : if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
576 [ + + ]: 381051 : (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
577 [ + + ]: 3 : !write_ok))
578 : : {
579 : 1 : SimpleLruWaitIO(ctl, slotno);
580 : : /* Now we must recheck state from the top */
581 : 1 : continue;
582 : : }
583 : : /* Otherwise, it's ready to use */
584 : 381050 : SlruRecentlyUsed(shared, slotno);
585 : :
586 : : /* update the stats counter of pages found in the SLRU */
587 : 381050 : pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
588 : :
589 : 381050 : return slotno;
590 : : }
591 : :
592 : : /* We found no match; assert we selected a freeable slot */
593 : : Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
594 : : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
595 : : !shared->page_dirty[slotno]));
596 : :
597 : : /* Mark the slot read-busy */
598 : 17645 : shared->page_number[slotno] = pageno;
599 : 17645 : shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS;
600 : 17645 : shared->page_dirty[slotno] = false;
601 : :
602 : : /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
603 : 17645 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
604 : :
605 : : /* Release bank lock while doing I/O */
606 : 17645 : LWLockRelease(banklock);
607 : :
608 : : /* Do the read */
609 : 17645 : ok = SlruPhysicalReadPage(ctl, pageno, slotno);
610 : :
611 : : /* Set the LSNs for this newly read-in page to zero */
612 : 17645 : SimpleLruZeroLSNs(ctl, slotno);
613 : :
614 : : /* Re-acquire bank control lock and update page state */
615 : 17645 : LWLockAcquire(banklock, LW_EXCLUSIVE);
616 : :
617 : : Assert(shared->page_number[slotno] == pageno &&
618 : : shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS &&
619 : : !shared->page_dirty[slotno]);
620 : :
621 [ + + ]: 17645 : shared->page_status[slotno] = ok ? SLRU_PAGE_VALID : SLRU_PAGE_EMPTY;
622 : :
623 : 17645 : LWLockRelease(&shared->buffer_locks[slotno].lock);
624 : :
625 : : /* Now it's okay to ereport if we failed */
626 [ + + ]: 17645 : if (!ok)
627 : 1 : SlruReportIOError(ctl, pageno, opaque_data);
628 : :
629 : 17644 : SlruRecentlyUsed(shared, slotno);
630 : :
631 : : /* update the stats counter of pages not found in SLRU */
632 : 17644 : pgstat_count_slru_blocks_read(shared->slru_stats_idx);
633 : :
634 : 17644 : return slotno;
635 : : }
636 : : }
637 : :
638 : : /*
639 : : * Find a page in a shared buffer, reading it in if necessary.
640 : : * The page number must correspond to an already-initialized page.
641 : : * The caller must intend only read-only access to the page.
642 : : *
643 : : * On error, the passed-in 'opaque_data' is passed to the
644 : : * 'errdetail_for_io_error' callback, to provide details on the operation that
645 : : * failed. It is only used for error reporting.
646 : : *
647 : : * Return value is the shared-buffer slot number now holding the page.
648 : : * The buffer's LRU access info is updated.
649 : : *
650 : : * Bank control lock must NOT be held at entry, but will be held at exit.
651 : : * It is unspecified whether the lock will be shared or exclusive.
652 : : */
653 : : int
654 : 919034 : SimpleLruReadPage_ReadOnly(SlruDesc *ctl, int64 pageno, const void *opaque_data)
655 : : {
656 : 919034 : SlruShared shared = ctl->shared;
657 : 919034 : LWLock *banklock = SimpleLruGetBankLock(ctl, pageno);
658 : 919034 : int bankno = pageno % ctl->nbanks;
659 : 919034 : int bankstart = bankno * SLRU_BANK_SIZE;
660 : 919034 : int bankend = bankstart + SLRU_BANK_SIZE;
661 : :
662 : : /* Try to find the page while holding only shared lock */
663 : 919034 : LWLockAcquire(banklock, LW_SHARED);
664 : :
665 : : /* See if page is already in a buffer */
666 [ + + ]: 925262 : for (int slotno = bankstart; slotno < bankend; slotno++)
667 : : {
668 [ + + ]: 925036 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
669 [ + + ]: 923949 : shared->page_number[slotno] == pageno &&
670 [ + - ]: 918808 : shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
671 : : {
672 : : /* See comments for SlruRecentlyUsed() */
673 : 918808 : SlruRecentlyUsed(shared, slotno);
674 : :
675 : : /* update the stats counter of pages found in the SLRU */
676 : 918808 : pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
677 : :
678 : 918808 : return slotno;
679 : : }
680 : : }
681 : :
682 : : /* No luck, so switch to normal exclusive lock and do regular read */
683 : 226 : LWLockRelease(banklock);
684 : 226 : LWLockAcquire(banklock, LW_EXCLUSIVE);
685 : :
686 : 226 : return SimpleLruReadPage(ctl, pageno, true, opaque_data);
687 : : }
688 : :
689 : : /*
690 : : * Write a page from a shared buffer, if necessary.
691 : : * Does nothing if the specified slot is not dirty.
692 : : *
693 : : * NOTE: only one write attempt is made here. Hence, it is possible that
694 : : * the page is still dirty at exit (if someone else re-dirtied it during
695 : : * the write). However, we *do* attempt a fresh write even if the page
696 : : * is already being written; this is for checkpoints.
697 : : *
698 : : * Bank lock must be held at entry, and will be held at exit.
699 : : */
700 : : static void
701 : 7350261 : SlruInternalWritePage(SlruDesc *ctl, int slotno, SlruWriteAll fdata)
702 : : {
703 : 7350261 : SlruShared shared = ctl->shared;
704 : 7350261 : int64 pageno = shared->page_number[slotno];
705 : 7350261 : int bankno = SlotGetBankNumber(slotno);
706 : : bool ok;
707 : :
708 : : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
709 : : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
710 : :
711 : : /* If a write is in progress, wait for it to finish */
712 [ - + ]: 7350261 : while (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
713 [ # # ]: 0 : shared->page_number[slotno] == pageno)
714 : : {
715 : 0 : SimpleLruWaitIO(ctl, slotno);
716 : : }
717 : :
718 : : /*
719 : : * Do nothing if page is not dirty, or if buffer no longer contains the
720 : : * same page we were called for.
721 : : */
722 [ + + ]: 7350261 : if (!shared->page_dirty[slotno] ||
723 [ + - ]: 7346755 : shared->page_status[slotno] != SLRU_PAGE_VALID ||
724 [ - + ]: 7346755 : shared->page_number[slotno] != pageno)
725 : 3506 : return;
726 : :
727 : : /*
728 : : * Mark the slot write-busy, and clear the dirtybit. After this point, a
729 : : * transaction status update on this page will mark it dirty again.
730 : : */
731 : 7346755 : shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS;
732 : 7346755 : shared->page_dirty[slotno] = false;
733 : :
734 : : /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
735 : 7346755 : LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
736 : :
737 : : /* Release bank lock while doing I/O */
738 : 7346755 : LWLockRelease(&shared->bank_locks[bankno].lock);
739 : :
740 : : /* Do the write */
741 : 7346755 : ok = SlruPhysicalWritePage(ctl, pageno, slotno, fdata);
742 : :
743 : : /* If we failed, and we're in a flush, better close the files */
744 [ - + - - ]: 7346755 : if (!ok && fdata)
745 : : {
746 [ # # ]: 0 : for (int i = 0; i < fdata->num_files; i++)
747 : 0 : CloseTransientFile(fdata->fd[i]);
748 : : }
749 : :
750 : : /* Re-acquire bank lock and update page state */
751 : 7346755 : LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
752 : :
753 : : Assert(shared->page_number[slotno] == pageno &&
754 : : shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS);
755 : :
756 : : /* If we failed to write, mark the page dirty again */
757 [ - + ]: 7346755 : if (!ok)
758 : 0 : shared->page_dirty[slotno] = true;
759 : :
760 : 7346755 : shared->page_status[slotno] = SLRU_PAGE_VALID;
761 : :
762 : 7346755 : LWLockRelease(&shared->buffer_locks[slotno].lock);
763 : :
764 : : /* Now it's okay to ereport if we failed */
765 [ - + ]: 7346755 : if (!ok)
766 : 0 : SlruReportIOError(ctl, pageno, NULL);
767 : :
768 : : /* If part of a checkpoint, count this as a SLRU buffer written. */
769 [ + + ]: 7346755 : if (fdata)
770 : : {
771 : 3172 : CheckpointStats.ckpt_slru_written++;
772 : 3172 : PendingCheckpointerStats.slru_written++;
773 : : }
774 : : }
775 : :
776 : : /*
777 : : * Wrapper of SlruInternalWritePage, for external callers.
778 : : * fdata is always passed a NULL here.
779 : : */
780 : : void
781 : 340 : SimpleLruWritePage(SlruDesc *ctl, int slotno)
782 : : {
783 : : Assert(ctl->shared->page_status[slotno] != SLRU_PAGE_EMPTY);
784 : :
785 : 340 : SlruInternalWritePage(ctl, slotno, NULL);
786 : 340 : }
787 : :
788 : : /*
789 : : * Return whether the given page exists on disk.
790 : : *
791 : : * A false return means that either the file does not exist, or that it's not
792 : : * large enough to contain the given page.
793 : : */
794 : : bool
795 : 66 : SimpleLruDoesPhysicalPageExist(SlruDesc *ctl, int64 pageno)
796 : : {
797 : 66 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
798 : 66 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
799 : 66 : int offset = rpageno * BLCKSZ;
800 : : char path[MAXPGPATH];
801 : : int fd;
802 : : bool result;
803 : : off_t endpos;
804 : :
805 : : /* update the stats counter of checked pages */
806 : 66 : pgstat_count_slru_blocks_exists(ctl->shared->slru_stats_idx);
807 : :
808 : 66 : SlruFileName(ctl, path, segno);
809 : :
810 : 66 : fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
811 [ + + ]: 66 : if (fd < 0)
812 : : {
813 : : /* expected: file doesn't exist */
814 [ + - ]: 26 : if (errno == ENOENT)
815 : 26 : return false;
816 : :
817 : : /* report error normally */
818 : 0 : slru_errcause = SLRU_OPEN_FAILED;
819 : 0 : slru_errno = errno;
820 : 0 : SlruReportIOError(ctl, pageno, NULL);
821 : : }
822 : :
823 [ - + ]: 40 : if ((endpos = lseek(fd, 0, SEEK_END)) < 0)
824 : : {
825 : 0 : slru_errcause = SLRU_SEEK_FAILED;
826 : 0 : slru_errno = errno;
827 : 0 : SlruReportIOError(ctl, pageno, NULL);
828 : : }
829 : :
830 : 40 : result = endpos >= (off_t) (offset + BLCKSZ);
831 : :
832 [ - + ]: 40 : if (CloseTransientFile(fd) != 0)
833 : : {
834 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
835 : 0 : slru_errno = errno;
836 : 0 : return false;
837 : : }
838 : :
839 : 40 : return result;
840 : : }
841 : :
842 : : /*
843 : : * Physical read of a (previously existing) page into a buffer slot
844 : : *
845 : : * On failure, we cannot just ereport(ERROR) since caller has put state in
846 : : * shared memory that must be undone. So, we return false and save enough
847 : : * info in static variables to let SlruReportIOError make the report.
848 : : *
849 : : * For now, assume it's not worth keeping a file pointer open across
850 : : * read/write operations. We could cache one virtual file pointer ...
851 : : */
852 : : static bool
853 : 17645 : SlruPhysicalReadPage(SlruDesc *ctl, int64 pageno, int slotno)
854 : : {
855 : 17645 : SlruShared shared = ctl->shared;
856 : 17645 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
857 : 17645 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
858 : 17645 : off_t offset = rpageno * BLCKSZ;
859 : : char path[MAXPGPATH];
860 : : int fd;
861 : :
862 : 17645 : SlruFileName(ctl, path, segno);
863 : :
864 : : /*
865 : : * In a crash-and-restart situation, it's possible for us to receive
866 : : * commands to set the commit status of transactions whose bits are in
867 : : * already-truncated segments of the commit log (see notes in
868 : : * SlruPhysicalWritePage). Hence, if we are InRecovery, allow the case
869 : : * where the file doesn't exist, and return zeroes instead.
870 : : */
871 : 17645 : fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
872 [ + + ]: 17645 : if (fd < 0)
873 : : {
874 [ + - + - ]: 1 : if (errno != ENOENT || !InRecovery)
875 : : {
876 : 1 : slru_errcause = SLRU_OPEN_FAILED;
877 : 1 : slru_errno = errno;
878 : 1 : return false;
879 : : }
880 : :
881 [ # # ]: 0 : ereport(LOG,
882 : : (errmsg("file \"%s\" doesn't exist, reading as zeroes",
883 : : path)));
884 [ # # # # : 0 : MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
# # # # #
# ]
885 : 0 : return true;
886 : : }
887 : :
888 : 17644 : errno = 0;
889 : 17644 : pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
890 [ - + ]: 17644 : if (pg_pread(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
891 : : {
892 : 0 : pgstat_report_wait_end();
893 : 0 : slru_errcause = SLRU_READ_FAILED;
894 : 0 : slru_errno = errno;
895 : 0 : CloseTransientFile(fd);
896 : 0 : return false;
897 : : }
898 : 17644 : pgstat_report_wait_end();
899 : :
900 [ - + ]: 17644 : if (CloseTransientFile(fd) != 0)
901 : : {
902 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
903 : 0 : slru_errno = errno;
904 : 0 : return false;
905 : : }
906 : :
907 : 17644 : return true;
908 : : }
909 : :
910 : : /*
911 : : * Physical write of a page from a buffer slot
912 : : *
913 : : * On failure, we cannot just ereport(ERROR) since caller has put state in
914 : : * shared memory that must be undone. So, we return false and save enough
915 : : * info in static variables to let SlruReportIOError make the report.
916 : : *
917 : : * For now, assume it's not worth keeping a file pointer open across
918 : : * independent read/write operations. We do batch operations during
919 : : * SimpleLruWriteAll, though.
920 : : *
921 : : * fdata is NULL for a standalone write, pointer to open-file info during
922 : : * SimpleLruWriteAll.
923 : : */
924 : : static bool
925 : 7346755 : SlruPhysicalWritePage(SlruDesc *ctl, int64 pageno, int slotno, SlruWriteAll fdata)
926 : : {
927 : 7346755 : SlruShared shared = ctl->shared;
928 : 7346755 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
929 : 7346755 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
930 : 7346755 : off_t offset = rpageno * BLCKSZ;
931 : : char path[MAXPGPATH];
932 : 7346755 : int fd = -1;
933 : :
934 : : /* update the stats counter of written pages */
935 : 7346755 : pgstat_count_slru_blocks_written(shared->slru_stats_idx);
936 : :
937 : : /*
938 : : * Honor the write-WAL-before-data rule, if appropriate, so that we do not
939 : : * write out data before associated WAL records. This is the same action
940 : : * performed during FlushBuffer() in the main buffer manager.
941 : : */
942 [ + + ]: 7346755 : if (shared->group_lsn != NULL)
943 : : {
944 : : /*
945 : : * We must determine the largest async-commit LSN for the page. This
946 : : * is a bit tedious, but since this entire function is a slow path
947 : : * anyway, it seems better to do this here than to maintain a per-page
948 : : * LSN variable (which'd need an extra comparison in the
949 : : * transaction-commit path).
950 : : */
951 : : XLogRecPtr max_lsn;
952 : : int lsnindex;
953 : :
954 : 433428 : lsnindex = slotno * shared->lsn_groups_per_page;
955 : 433428 : max_lsn = shared->group_lsn[lsnindex++];
956 [ + + ]: 443830272 : for (int lsnoff = 1; lsnoff < shared->lsn_groups_per_page; lsnoff++)
957 : : {
958 : 443396844 : XLogRecPtr this_lsn = shared->group_lsn[lsnindex++];
959 : :
960 [ + + ]: 443396844 : if (max_lsn < this_lsn)
961 : 51552 : max_lsn = this_lsn;
962 : : }
963 : :
964 [ + + ]: 433428 : if (XLogRecPtrIsValid(max_lsn))
965 : : {
966 : : /*
967 : : * As noted above, elog(ERROR) is not acceptable here, so if
968 : : * XLogFlush were to fail, we must PANIC. This isn't much of a
969 : : * restriction because XLogFlush is just about all critical
970 : : * section anyway, but let's make sure.
971 : : */
972 : 562 : START_CRIT_SECTION();
973 : 562 : XLogFlush(max_lsn);
974 : 562 : END_CRIT_SECTION();
975 : : }
976 : : }
977 : :
978 : : /*
979 : : * During a SimpleLruWriteAll, we may already have the desired file open.
980 : : */
981 [ + + ]: 7346755 : if (fdata)
982 : : {
983 [ + + ]: 3279 : for (int i = 0; i < fdata->num_files; i++)
984 : : {
985 [ + + ]: 348 : if (fdata->segno[i] == segno)
986 : : {
987 : 241 : fd = fdata->fd[i];
988 : 241 : break;
989 : : }
990 : : }
991 : : }
992 : :
993 [ + + ]: 7346755 : if (fd < 0)
994 : : {
995 : : /*
996 : : * If the file doesn't already exist, we should create it. It is
997 : : * possible for this to need to happen when writing a page that's not
998 : : * first in its segment; we assume the OS can cope with that. (Note:
999 : : * it might seem that it'd be okay to create files only when
1000 : : * SimpleLruZeroPage is called for the first page of a segment.
1001 : : * However, if after a crash and restart the REDO logic elects to
1002 : : * replay the log from a checkpoint before the latest one, then it's
1003 : : * possible that we will get commands to set transaction status of
1004 : : * transactions that have already been truncated from the commit log.
1005 : : * Easiest way to deal with that is to accept references to
1006 : : * nonexistent files here and in SlruPhysicalReadPage.)
1007 : : *
1008 : : * Note: it is possible for more than one backend to be executing this
1009 : : * code simultaneously for different pages of the same file. Hence,
1010 : : * don't use O_EXCL or O_TRUNC or anything like that.
1011 : : */
1012 : 7346514 : SlruFileName(ctl, path, segno);
1013 : 7346514 : fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY);
1014 [ - + ]: 7346514 : if (fd < 0)
1015 : : {
1016 : 0 : slru_errcause = SLRU_OPEN_FAILED;
1017 : 0 : slru_errno = errno;
1018 : 0 : return false;
1019 : : }
1020 : :
1021 [ + + ]: 7346514 : if (fdata)
1022 : : {
1023 [ + - ]: 2931 : if (fdata->num_files < MAX_WRITEALL_BUFFERS)
1024 : : {
1025 : 2931 : fdata->fd[fdata->num_files] = fd;
1026 : 2931 : fdata->segno[fdata->num_files] = segno;
1027 : 2931 : fdata->num_files++;
1028 : : }
1029 : : else
1030 : : {
1031 : : /*
1032 : : * In the unlikely event that we exceed MAX_WRITEALL_BUFFERS,
1033 : : * fall back to treating it as a standalone write.
1034 : : */
1035 : 0 : fdata = NULL;
1036 : : }
1037 : : }
1038 : : }
1039 : :
1040 : 7346755 : errno = 0;
1041 : 7346755 : pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE);
1042 [ - + ]: 7346755 : if (pg_pwrite(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
1043 : : {
1044 : 0 : pgstat_report_wait_end();
1045 : : /* if write didn't set errno, assume problem is no disk space */
1046 [ # # ]: 0 : if (errno == 0)
1047 : 0 : errno = ENOSPC;
1048 : 0 : slru_errcause = SLRU_WRITE_FAILED;
1049 : 0 : slru_errno = errno;
1050 [ # # ]: 0 : if (!fdata)
1051 : 0 : CloseTransientFile(fd);
1052 : 0 : return false;
1053 : : }
1054 : 7346755 : pgstat_report_wait_end();
1055 : :
1056 : : /* Queue up a sync request for the checkpointer. */
1057 [ + + ]: 7346755 : if (ctl->options.sync_handler != SYNC_HANDLER_NONE)
1058 : : {
1059 : : FileTag tag;
1060 : :
1061 : 434385 : INIT_SLRUFILETAG(tag, ctl->options.sync_handler, segno);
1062 [ + + ]: 434385 : if (!RegisterSyncRequest(&tag, SYNC_REQUEST, false))
1063 : : {
1064 : : /* No space to enqueue sync request. Do it synchronously. */
1065 : 5 : pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC);
1066 [ - + ]: 5 : if (pg_fsync(fd) != 0)
1067 : : {
1068 : 0 : pgstat_report_wait_end();
1069 : 0 : slru_errcause = SLRU_FSYNC_FAILED;
1070 : 0 : slru_errno = errno;
1071 : 0 : CloseTransientFile(fd);
1072 : 0 : return false;
1073 : : }
1074 : 5 : pgstat_report_wait_end();
1075 : : }
1076 : : }
1077 : :
1078 : : /* Close file, unless part of flush request. */
1079 [ + + ]: 7346755 : if (!fdata)
1080 : : {
1081 [ - + ]: 7343583 : if (CloseTransientFile(fd) != 0)
1082 : : {
1083 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
1084 : 0 : slru_errno = errno;
1085 : 0 : return false;
1086 : : }
1087 : : }
1088 : :
1089 : 7346755 : return true;
1090 : : }
1091 : :
1092 : : /*
1093 : : * Issue the error message after failure of SlruPhysicalReadPage or
1094 : : * SlruPhysicalWritePage. Call this after cleaning up shared-memory state.
1095 : : */
1096 : : static void
1097 : 1 : SlruReportIOError(SlruDesc *ctl, int64 pageno, const void *opaque_data)
1098 : : {
1099 : 1 : int64 segno = pageno / SLRU_PAGES_PER_SEGMENT;
1100 : 1 : int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
1101 : 1 : int offset = rpageno * BLCKSZ;
1102 : : char path[MAXPGPATH];
1103 : :
1104 : 1 : SlruFileName(ctl, path, segno);
1105 : 1 : errno = slru_errno;
1106 [ + - - - : 1 : switch (slru_errcause)
- - - ]
1107 : : {
1108 : 1 : case SLRU_OPEN_FAILED:
1109 [ + - + - ]: 1 : ereport(ERROR,
1110 : : (errcode_for_file_access(),
1111 : : errmsg("could not open file \"%s\": %m", path),
1112 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1113 : : break;
1114 : 0 : case SLRU_SEEK_FAILED:
1115 [ # # # # ]: 0 : ereport(ERROR,
1116 : : (errcode_for_file_access(),
1117 : : errmsg("could not seek in file \"%s\" to offset %d: %m",
1118 : : path, offset),
1119 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1120 : : break;
1121 : 0 : case SLRU_READ_FAILED:
1122 [ # # ]: 0 : if (errno)
1123 [ # # # # ]: 0 : ereport(ERROR,
1124 : : (errcode_for_file_access(),
1125 : : errmsg("could not read from file \"%s\" at offset %d: %m",
1126 : : path, offset),
1127 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1128 : : else
1129 [ # # # # ]: 0 : ereport(ERROR,
1130 : : (errmsg("could not read from file \"%s\" at offset %d: read too few bytes",
1131 : : path, offset),
1132 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1133 : : break;
1134 : 0 : case SLRU_WRITE_FAILED:
1135 [ # # ]: 0 : if (errno)
1136 [ # # # # ]: 0 : ereport(ERROR,
1137 : : (errcode_for_file_access(),
1138 : : errmsg("Could not write to file \"%s\" at offset %d: %m",
1139 : : path, offset),
1140 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1141 : : else
1142 [ # # # # ]: 0 : ereport(ERROR,
1143 : : (errmsg("Could not write to file \"%s\" at offset %d: wrote too few bytes.",
1144 : : path, offset),
1145 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1146 : : break;
1147 : 0 : case SLRU_FSYNC_FAILED:
1148 [ # # # # ]: 0 : ereport(data_sync_elevel(ERROR),
1149 : : (errcode_for_file_access(),
1150 : : errmsg("could not fsync file \"%s\": %m",
1151 : : path),
1152 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1153 : 0 : break;
1154 : 0 : case SLRU_CLOSE_FAILED:
1155 [ # # # # ]: 0 : ereport(ERROR,
1156 : : (errcode_for_file_access(),
1157 : : errmsg("could not close file \"%s\": %m",
1158 : : path),
1159 : : opaque_data ? ctl->options.errdetail_for_io_error(opaque_data) : 0));
1160 : : break;
1161 : 0 : default:
1162 : : /* can't get here, we trust */
1163 [ # # ]: 0 : elog(ERROR, "unrecognized SimpleLru error cause: %d",
1164 : : (int) slru_errcause);
1165 : : break;
1166 : : }
1167 : 0 : }
1168 : :
1169 : : /*
1170 : : * Mark a buffer slot "most recently used".
1171 : : */
1172 : : static inline void
1173 : 8663535 : SlruRecentlyUsed(SlruShared shared, int slotno)
1174 : : {
1175 : 8663535 : int bankno = SlotGetBankNumber(slotno);
1176 : 8663535 : int new_lru_count = shared->bank_cur_lru_count[bankno];
1177 : :
1178 : : Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
1179 : :
1180 : : /*
1181 : : * The reason for the if-test is that there are often many consecutive
1182 : : * accesses to the same page (particularly the latest page). By
1183 : : * suppressing useless increments of bank_cur_lru_count, we reduce the
1184 : : * probability that old pages' counts will "wrap around" and make them
1185 : : * appear recently used.
1186 : : *
1187 : : * We allow this code to be executed concurrently by multiple processes
1188 : : * within SimpleLruReadPage_ReadOnly(). As long as int reads and writes
1189 : : * are atomic, this should not cause any completely-bogus values to enter
1190 : : * the computation. However, it is possible for either bank_cur_lru_count
1191 : : * or individual page_lru_count entries to be "reset" to lower values than
1192 : : * they should have, in case a process is delayed while it executes this
1193 : : * function. With care in SlruSelectLRUPage(), this does little harm, and
1194 : : * in any case the absolute worst possible consequence is a nonoptimal
1195 : : * choice of page to evict. The gain from allowing concurrent reads of
1196 : : * SLRU pages seems worth it.
1197 : : */
1198 [ + + ]: 8663535 : if (new_lru_count != shared->page_lru_count[slotno])
1199 : : {
1200 : 7484243 : shared->bank_cur_lru_count[bankno] = ++new_lru_count;
1201 : 7484243 : shared->page_lru_count[slotno] = new_lru_count;
1202 : : }
1203 : 8663535 : }
1204 : :
1205 : : /*
1206 : : * Select the slot to re-use when we need a free slot for the given page.
1207 : : *
1208 : : * The target page number is passed not only because we need to know the
1209 : : * correct bank to use, but also because we need to consider the possibility
1210 : : * that some other process reads in the target page while we are doing I/O to
1211 : : * free a slot. Hence, check or recheck to see if any slot already holds the
1212 : : * target page, and return that slot if so. Thus, the returned slot is
1213 : : * *either* a slot already holding the pageno (could be any state except
1214 : : * EMPTY), *or* a freeable slot (state EMPTY or CLEAN).
1215 : : *
1216 : : * The correct bank lock must be held at entry, and will be held at exit.
1217 : : */
1218 : : static int
1219 : 7744729 : SlruSelectLRUPage(SlruDesc *ctl, int64 pageno)
1220 : : {
1221 : 7744729 : SlruShared shared = ctl->shared;
1222 : :
1223 : : /* Outer loop handles restart after I/O */
1224 : : for (;;)
1225 : 7343191 : {
1226 : : int cur_count;
1227 : 15087920 : int bestvalidslot = 0; /* keep compiler quiet */
1228 : 15087920 : int best_valid_delta = -1;
1229 : 15087920 : int64 best_valid_page_number = 0; /* keep compiler quiet */
1230 : 15087920 : int bestinvalidslot = 0; /* keep compiler quiet */
1231 : 15087920 : int best_invalid_delta = -1;
1232 : 15087920 : int64 best_invalid_page_number = 0; /* keep compiler quiet */
1233 : 15087920 : int bankno = pageno % ctl->nbanks;
1234 : 15087920 : int bankstart = bankno * SLRU_BANK_SIZE;
1235 : 15087920 : int bankend = bankstart + SLRU_BANK_SIZE;
1236 : :
1237 : : Assert(LWLockHeldByMe(SimpleLruGetBankLock(ctl, pageno)));
1238 : :
1239 : : /* See if page already has a buffer assigned */
1240 [ + + ]: 251032861 : for (int slotno = bankstart; slotno < bankend; slotno++)
1241 : : {
1242 [ + + ]: 236326217 : if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
1243 [ + + ]: 236269126 : shared->page_number[slotno] == pageno)
1244 : 381276 : return slotno;
1245 : : }
1246 : :
1247 : : /*
1248 : : * If we find any EMPTY slot, just select that one. Else choose a
1249 : : * victim page to replace. We normally take the least recently used
1250 : : * valid page, but we will never take the slot containing
1251 : : * latest_page_number, even if it appears least recently used. We
1252 : : * will select a slot that is already I/O busy only if there is no
1253 : : * other choice: a read-busy slot will not be least recently used once
1254 : : * the read finishes, and waiting for an I/O on a write-busy slot is
1255 : : * inferior to just picking some other slot. Testing shows the slot
1256 : : * we pick instead will often be clean, allowing us to begin a read at
1257 : : * once.
1258 : : *
1259 : : * Normally the page_lru_count values will all be different and so
1260 : : * there will be a well-defined LRU page. But since we allow
1261 : : * concurrent execution of SlruRecentlyUsed() within
1262 : : * SimpleLruReadPage_ReadOnly(), it is possible that multiple pages
1263 : : * acquire the same lru_count values. In that case we break ties by
1264 : : * choosing the furthest-back page.
1265 : : *
1266 : : * Notice that this next line forcibly advances cur_lru_count to a
1267 : : * value that is certainly beyond any value that will be in the
1268 : : * page_lru_count array after the loop finishes. This ensures that
1269 : : * the next execution of SlruRecentlyUsed will mark the page newly
1270 : : * used, even if it's for a page that has the current counter value.
1271 : : * That gets us back on the path to having good data when there are
1272 : : * multiple pages with the same lru_count.
1273 : : */
1274 : 14706644 : cur_count = (shared->bank_cur_lru_count[bankno])++;
1275 [ + + ]: 249955905 : for (int slotno = bankstart; slotno < bankend; slotno++)
1276 : : {
1277 : : int this_delta;
1278 : : int64 this_page_number;
1279 : :
1280 [ + + ]: 235253018 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1281 : 3757 : return slotno;
1282 : :
1283 : 235249261 : this_delta = cur_count - shared->page_lru_count[slotno];
1284 [ - + ]: 235249261 : if (this_delta < 0)
1285 : : {
1286 : : /*
1287 : : * Clean up in case shared updates have caused cur_count
1288 : : * increments to get "lost". We back off the page counts,
1289 : : * rather than trying to increase cur_count, to avoid any
1290 : : * question of infinite loops or failure in the presence of
1291 : : * wrapped-around counts.
1292 : : */
1293 : 0 : shared->page_lru_count[slotno] = cur_count;
1294 : 0 : this_delta = 0;
1295 : : }
1296 : :
1297 : : /*
1298 : : * If this page is the one most recently zeroed, don't consider it
1299 : : * an eviction candidate. See comments in SimpleLruZeroPage for an
1300 : : * explanation about the lack of a memory barrier here.
1301 : : */
1302 : 235249261 : this_page_number = shared->page_number[slotno];
1303 [ + + ]: 235249261 : if (this_page_number ==
1304 : 235249261 : pg_atomic_read_u64(&shared->latest_page_number))
1305 : 8882 : continue;
1306 : :
1307 [ + + ]: 235240379 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1308 : : {
1309 [ + + - + ]: 235240021 : if (this_delta > best_valid_delta ||
1310 [ # # ]: 0 : (this_delta == best_valid_delta &&
1311 : 0 : ctl->options.PagePrecedes(this_page_number,
1312 : : best_valid_page_number)))
1313 : : {
1314 : 37618698 : bestvalidslot = slotno;
1315 : 37618698 : best_valid_delta = this_delta;
1316 : 37618698 : best_valid_page_number = this_page_number;
1317 : : }
1318 : : }
1319 : : else
1320 : : {
1321 [ - + - - ]: 358 : if (this_delta > best_invalid_delta ||
1322 [ # # ]: 0 : (this_delta == best_invalid_delta &&
1323 : 0 : ctl->options.PagePrecedes(this_page_number,
1324 : : best_invalid_page_number)))
1325 : : {
1326 : 358 : bestinvalidslot = slotno;
1327 : 358 : best_invalid_delta = this_delta;
1328 : 358 : best_invalid_page_number = this_page_number;
1329 : : }
1330 : : }
1331 : : }
1332 : :
1333 : : /*
1334 : : * If all pages (except possibly the latest one) are I/O busy, we'll
1335 : : * have to wait for an I/O to complete and then retry. In that
1336 : : * unhappy case, we choose to wait for the I/O on the least recently
1337 : : * used slot, on the assumption that it was likely initiated first of
1338 : : * all the I/Os in progress and may therefore finish first.
1339 : : */
1340 [ - + ]: 14702887 : if (best_valid_delta < 0)
1341 : : {
1342 : 0 : SimpleLruWaitIO(ctl, bestinvalidslot);
1343 : 0 : continue;
1344 : : }
1345 : :
1346 : : /*
1347 : : * If the selected page is clean, we're set.
1348 : : */
1349 [ + + ]: 14702887 : if (!shared->page_dirty[bestvalidslot])
1350 : 7359696 : return bestvalidslot;
1351 : :
1352 : : /*
1353 : : * Write the page.
1354 : : */
1355 : 7343191 : SlruInternalWritePage(ctl, bestvalidslot, NULL);
1356 : :
1357 : : /*
1358 : : * Now loop back and try again. This is the easiest way of dealing
1359 : : * with corner cases such as the victim page being re-dirtied while we
1360 : : * wrote it.
1361 : : */
1362 : : }
1363 : : }
1364 : :
1365 : : /*
1366 : : * Write dirty pages to disk during checkpoint or database shutdown. Flushing
1367 : : * is deferred until the next call to ProcessSyncRequests(), though we do fsync
1368 : : * the containing directory here to make sure that newly created directory
1369 : : * entries are on disk.
1370 : : */
1371 : : void
1372 : 9777 : SimpleLruWriteAll(SlruDesc *ctl, bool allow_redirtied)
1373 : : {
1374 : 9777 : SlruShared shared = ctl->shared;
1375 : : SlruWriteAllData fdata;
1376 : 9777 : int64 pageno = 0;
1377 : 9777 : int prevbank = SlotGetBankNumber(0);
1378 : : bool ok;
1379 : :
1380 : : /* update the stats counter of flushes */
1381 : 9777 : pgstat_count_slru_flush(shared->slru_stats_idx);
1382 : :
1383 : : /*
1384 : : * Find and write dirty pages
1385 : : */
1386 : 9777 : fdata.num_files = 0;
1387 : :
1388 : 9777 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1389 : :
1390 [ + + ]: 238337 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1391 : : {
1392 : 228560 : int curbank = SlotGetBankNumber(slotno);
1393 : :
1394 : : /*
1395 : : * If the current bank lock is not same as the previous bank lock then
1396 : : * release the previous lock and acquire the new lock.
1397 : : */
1398 [ + + ]: 228560 : if (curbank != prevbank)
1399 : : {
1400 : 4508 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1401 : 4508 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1402 : 4508 : prevbank = curbank;
1403 : : }
1404 : :
1405 : : /* Do nothing if slot is unused */
1406 [ + + ]: 228560 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1407 : 221882 : continue;
1408 : :
1409 : 6678 : SlruInternalWritePage(ctl, slotno, &fdata);
1410 : :
1411 : : /*
1412 : : * In some places (e.g. checkpoints), we cannot assert that the slot
1413 : : * is clean now, since another process might have re-dirtied it
1414 : : * already. That's okay.
1415 : : */
1416 : : Assert(allow_redirtied ||
1417 : : shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
1418 : : (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1419 : : !shared->page_dirty[slotno]));
1420 : : }
1421 : :
1422 : 9777 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1423 : :
1424 : : /*
1425 : : * Now close any files that were open
1426 : : */
1427 : 9777 : ok = true;
1428 [ + + ]: 12708 : for (int i = 0; i < fdata.num_files; i++)
1429 : : {
1430 [ - + ]: 2931 : if (CloseTransientFile(fdata.fd[i]) != 0)
1431 : : {
1432 : 0 : slru_errcause = SLRU_CLOSE_FAILED;
1433 : 0 : slru_errno = errno;
1434 : 0 : pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT;
1435 : 0 : ok = false;
1436 : : }
1437 : : }
1438 [ - + ]: 9777 : if (!ok)
1439 : 0 : SlruReportIOError(ctl, pageno, NULL);
1440 : :
1441 : : /* Ensure that directory entries for new files are on disk. */
1442 [ + + ]: 9777 : if (ctl->options.sync_handler != SYNC_HANDLER_NONE)
1443 : 7828 : fsync_fname(ctl->options.Dir, true);
1444 : 9777 : }
1445 : :
1446 : : /*
1447 : : * Remove all segments before the one holding the passed page number
1448 : : *
1449 : : * All SLRUs prevent concurrent calls to this function, either with an LWLock
1450 : : * or by calling it only as part of a checkpoint. Mutual exclusion must begin
1451 : : * before computing cutoffPage. Mutual exclusion must end after any limit
1452 : : * update that would permit other backends to write fresh data into the
1453 : : * segment immediately preceding the one containing cutoffPage. Otherwise,
1454 : : * when the SLRU is quite full, SimpleLruTruncate() might delete that segment
1455 : : * after it has accrued freshly-written data.
1456 : : */
1457 : : void
1458 : 2015 : SimpleLruTruncate(SlruDesc *ctl, int64 cutoffPage)
1459 : : {
1460 : 2015 : SlruShared shared = ctl->shared;
1461 : : int prevbank;
1462 : :
1463 : : /* update the stats counter of truncates */
1464 : 2015 : pgstat_count_slru_truncate(shared->slru_stats_idx);
1465 : :
1466 : : /*
1467 : : * Scan shared memory and remove any pages preceding the cutoff page, to
1468 : : * ensure we won't rewrite them later. (Since this is normally called in
1469 : : * or just after a checkpoint, any dirty pages should have been flushed
1470 : : * already ... we're just being extra careful here.)
1471 : : */
1472 : 2067 : restart:
1473 : :
1474 : : /*
1475 : : * An important safety check: the current endpoint page must not be
1476 : : * eligible for removal. This check is just a backstop against wraparound
1477 : : * bugs elsewhere in SLRU handling, so we don't care if we read a slightly
1478 : : * outdated value; therefore we don't add a memory barrier.
1479 : : */
1480 [ - + ]: 2067 : if (ctl->options.PagePrecedes(pg_atomic_read_u64(&shared->latest_page_number),
1481 : : cutoffPage))
1482 : : {
1483 [ # # ]: 0 : ereport(LOG,
1484 : : (errmsg("could not truncate directory \"%s\": apparent wraparound",
1485 : : ctl->options.Dir)));
1486 : 0 : return;
1487 : : }
1488 : :
1489 : 2067 : prevbank = SlotGetBankNumber(0);
1490 : 2067 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1491 [ + + ]: 49994 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1492 : : {
1493 : 47979 : int curbank = SlotGetBankNumber(slotno);
1494 : :
1495 : : /*
1496 : : * If the current bank lock is not same as the previous bank lock then
1497 : : * release the previous lock and acquire the new lock.
1498 : : */
1499 [ + + ]: 47979 : if (curbank != prevbank)
1500 : : {
1501 : 958 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1502 : 958 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1503 : 958 : prevbank = curbank;
1504 : : }
1505 : :
1506 [ + + ]: 47979 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1507 : 42672 : continue;
1508 [ + + ]: 5307 : if (!ctl->options.PagePrecedes(shared->page_number[slotno], cutoffPage))
1509 : 5062 : continue;
1510 : :
1511 : : /*
1512 : : * If page is clean, just change state to EMPTY (expected case).
1513 : : */
1514 [ + - ]: 245 : if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1515 [ + + ]: 245 : !shared->page_dirty[slotno])
1516 : : {
1517 : 193 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
1518 : 193 : continue;
1519 : : }
1520 : :
1521 : : /*
1522 : : * Hmm, we have (or may have) I/O operations acting on the page, so
1523 : : * we've got to wait for them to finish and then start again. This is
1524 : : * the same logic as in SlruSelectLRUPage. (XXX if page is dirty,
1525 : : * wouldn't it be OK to just discard it without writing it?
1526 : : * SlruMayDeleteSegment() uses a stricter qualification, so we might
1527 : : * not delete this page in the end; even if we don't delete it, we
1528 : : * won't have cause to read its data again. For now, keep the logic
1529 : : * the same as it was.)
1530 : : */
1531 [ + - ]: 52 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1532 : 52 : SlruInternalWritePage(ctl, slotno, NULL);
1533 : : else
1534 : 0 : SimpleLruWaitIO(ctl, slotno);
1535 : :
1536 : 52 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1537 : 52 : goto restart;
1538 : : }
1539 : :
1540 : 2015 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1541 : :
1542 : : /* Now we can remove the old segment(s) */
1543 : 2015 : (void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage);
1544 : : }
1545 : :
1546 : : /*
1547 : : * Delete an individual SLRU segment.
1548 : : *
1549 : : * NB: This does not touch the SLRU buffers themselves, callers have to ensure
1550 : : * they either can't yet contain anything, or have already been cleaned out.
1551 : : */
1552 : : static void
1553 : 141994 : SlruInternalDeleteSegment(SlruDesc *ctl, int64 segno)
1554 : : {
1555 : : char path[MAXPGPATH];
1556 : :
1557 : : /* Forget any fsync requests queued for this segment. */
1558 [ + + ]: 141994 : if (ctl->options.sync_handler != SYNC_HANDLER_NONE)
1559 : : {
1560 : : FileTag tag;
1561 : :
1562 : 13215 : INIT_SLRUFILETAG(tag, ctl->options.sync_handler, segno);
1563 : 13215 : RegisterSyncRequest(&tag, SYNC_FORGET_REQUEST, true);
1564 : : }
1565 : :
1566 : : /* Unlink the file. */
1567 : 141994 : SlruFileName(ctl, path, segno);
1568 [ - + ]: 141994 : ereport(DEBUG2, (errmsg_internal("removing file \"%s\"", path)));
1569 : 141994 : unlink(path);
1570 : 141994 : }
1571 : :
1572 : : /*
1573 : : * Delete an individual SLRU segment, identified by the segment number.
1574 : : */
1575 : : void
1576 : 2 : SlruDeleteSegment(SlruDesc *ctl, int64 segno)
1577 : : {
1578 : 2 : SlruShared shared = ctl->shared;
1579 : 2 : int prevbank = SlotGetBankNumber(0);
1580 : : bool did_write;
1581 : :
1582 : : /* Clean out any possibly existing references to the segment. */
1583 : 2 : LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
1584 : 2 : restart:
1585 : 2 : did_write = false;
1586 [ + + ]: 34 : for (int slotno = 0; slotno < shared->num_slots; slotno++)
1587 : : {
1588 : : int64 pagesegno;
1589 : 32 : int curbank = SlotGetBankNumber(slotno);
1590 : :
1591 : : /*
1592 : : * If the current bank lock is not same as the previous bank lock then
1593 : : * release the previous lock and acquire the new lock.
1594 : : */
1595 [ - + ]: 32 : if (curbank != prevbank)
1596 : : {
1597 : 0 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1598 : 0 : LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
1599 : 0 : prevbank = curbank;
1600 : : }
1601 : :
1602 [ - + ]: 32 : if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
1603 : 0 : continue;
1604 : :
1605 : 32 : pagesegno = shared->page_number[slotno] / SLRU_PAGES_PER_SEGMENT;
1606 : : /* not the segment we're looking for */
1607 [ + + ]: 32 : if (pagesegno != segno)
1608 : 7 : continue;
1609 : :
1610 : : /* If page is clean, just change state to EMPTY (expected case). */
1611 [ + - ]: 25 : if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
1612 [ + - ]: 25 : !shared->page_dirty[slotno])
1613 : : {
1614 : 25 : shared->page_status[slotno] = SLRU_PAGE_EMPTY;
1615 : 25 : continue;
1616 : : }
1617 : :
1618 : : /* Same logic as SimpleLruTruncate() */
1619 [ # # ]: 0 : if (shared->page_status[slotno] == SLRU_PAGE_VALID)
1620 : 0 : SlruInternalWritePage(ctl, slotno, NULL);
1621 : : else
1622 : 0 : SimpleLruWaitIO(ctl, slotno);
1623 : :
1624 : 0 : did_write = true;
1625 : : }
1626 : :
1627 : : /*
1628 : : * Be extra careful and re-check. The IO functions release the control
1629 : : * lock, so new pages could have been read in.
1630 : : */
1631 [ - + ]: 2 : if (did_write)
1632 : 0 : goto restart;
1633 : :
1634 : 2 : SlruInternalDeleteSegment(ctl, segno);
1635 : :
1636 : 2 : LWLockRelease(&shared->bank_locks[prevbank].lock);
1637 : 2 : }
1638 : :
1639 : : /*
1640 : : * Determine whether a segment is okay to delete.
1641 : : *
1642 : : * segpage is the first page of the segment, and cutoffPage is the oldest (in
1643 : : * PagePrecedes order) page in the SLRU containing still-useful data. Since
1644 : : * every core PagePrecedes callback implements "wrap around", check the
1645 : : * segment's first and last pages:
1646 : : *
1647 : : * first<cutoff && last<cutoff: yes
1648 : : * first<cutoff && last>=cutoff: no; cutoff falls inside this segment
1649 : : * first>=cutoff && last<cutoff: no; wrap point falls inside this segment
1650 : : * first>=cutoff && last>=cutoff: no; every page of this segment is too young
1651 : : */
1652 : : static bool
1653 : 1138987 : SlruMayDeleteSegment(SlruDesc *ctl, int64 segpage, int64 cutoffPage)
1654 : : {
1655 : 1138987 : int64 seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
1656 : :
1657 : : Assert(segpage % SLRU_PAGES_PER_SEGMENT == 0);
1658 : :
1659 [ + + + + ]: 1281684 : return (ctl->options.PagePrecedes(segpage, cutoffPage) &&
1660 : 142697 : ctl->options.PagePrecedes(seg_last_page, cutoffPage));
1661 : : }
1662 : :
1663 : : #ifdef USE_ASSERT_CHECKING
1664 : : static void
1665 : : SlruPagePrecedesTestOffset(SlruDesc *ctl, int per_page, uint32 offset)
1666 : : {
1667 : : TransactionId lhs,
1668 : : rhs;
1669 : : int64 newestPage,
1670 : : oldestPage;
1671 : : TransactionId newestXact,
1672 : : oldestXact;
1673 : :
1674 : : /* This must be called after the Slru has been initialized */
1675 : : Assert(ctl->options.PagePrecedes);
1676 : :
1677 : : /*
1678 : : * Compare an XID pair having undefined order (see RFC 1982), a pair at
1679 : : * "opposite ends" of the XID space. TransactionIdPrecedes() treats each
1680 : : * as preceding the other. If RHS is oldestXact, LHS is the first XID we
1681 : : * must not assign.
1682 : : */
1683 : : lhs = per_page + offset; /* skip first page to avoid non-normal XIDs */
1684 : : rhs = lhs + (1U << 31);
1685 : : Assert(TransactionIdPrecedes(lhs, rhs));
1686 : : Assert(TransactionIdPrecedes(rhs, lhs));
1687 : : Assert(!TransactionIdPrecedes(lhs - 1, rhs));
1688 : : Assert(TransactionIdPrecedes(rhs, lhs - 1));
1689 : : Assert(TransactionIdPrecedes(lhs + 1, rhs));
1690 : : Assert(!TransactionIdPrecedes(rhs, lhs + 1));
1691 : : Assert(!TransactionIdFollowsOrEquals(lhs, rhs));
1692 : : Assert(!TransactionIdFollowsOrEquals(rhs, lhs));
1693 : : Assert(!ctl->options.PagePrecedes(lhs / per_page, lhs / per_page));
1694 : : Assert(!ctl->options.PagePrecedes(lhs / per_page, rhs / per_page));
1695 : : Assert(!ctl->options.PagePrecedes(rhs / per_page, lhs / per_page));
1696 : : Assert(!ctl->options.PagePrecedes((lhs - per_page) / per_page, rhs / per_page));
1697 : : Assert(ctl->options.PagePrecedes(rhs / per_page, (lhs - 3 * per_page) / per_page));
1698 : : Assert(ctl->options.PagePrecedes(rhs / per_page, (lhs - 2 * per_page) / per_page));
1699 : : Assert(ctl->options.PagePrecedes(rhs / per_page, (lhs - 1 * per_page) / per_page)
1700 : : || (1U << 31) % per_page != 0); /* See CommitTsPagePrecedes() */
1701 : : Assert(ctl->options.PagePrecedes((lhs + 1 * per_page) / per_page, rhs / per_page)
1702 : : || (1U << 31) % per_page != 0);
1703 : : Assert(ctl->options.PagePrecedes((lhs + 2 * per_page) / per_page, rhs / per_page));
1704 : : Assert(ctl->options.PagePrecedes((lhs + 3 * per_page) / per_page, rhs / per_page));
1705 : : Assert(!ctl->options.PagePrecedes(rhs / per_page, (lhs + per_page) / per_page));
1706 : :
1707 : : /*
1708 : : * GetNewTransactionId() has assigned the last XID it can safely use, and
1709 : : * that XID is in the *LAST* page of the second segment. We must not
1710 : : * delete that segment.
1711 : : */
1712 : : newestPage = 2 * SLRU_PAGES_PER_SEGMENT - 1;
1713 : : newestXact = newestPage * per_page + offset;
1714 : : Assert(newestXact / per_page == newestPage);
1715 : : oldestXact = newestXact + 1;
1716 : : oldestXact -= 1U << 31;
1717 : : oldestPage = oldestXact / per_page;
1718 : : Assert(!SlruMayDeleteSegment(ctl,
1719 : : (newestPage -
1720 : : newestPage % SLRU_PAGES_PER_SEGMENT),
1721 : : oldestPage));
1722 : :
1723 : : /*
1724 : : * GetNewTransactionId() has assigned the last XID it can safely use, and
1725 : : * that XID is in the *FIRST* page of the second segment. We must not
1726 : : * delete that segment.
1727 : : */
1728 : : newestPage = SLRU_PAGES_PER_SEGMENT;
1729 : : newestXact = newestPage * per_page + offset;
1730 : : Assert(newestXact / per_page == newestPage);
1731 : : oldestXact = newestXact + 1;
1732 : : oldestXact -= 1U << 31;
1733 : : oldestPage = oldestXact / per_page;
1734 : : Assert(!SlruMayDeleteSegment(ctl,
1735 : : (newestPage -
1736 : : newestPage % SLRU_PAGES_PER_SEGMENT),
1737 : : oldestPage));
1738 : : }
1739 : :
1740 : : /*
1741 : : * Unit-test a PagePrecedes function.
1742 : : *
1743 : : * This assumes every uint32 >= FirstNormalTransactionId is a valid key. It
1744 : : * assumes each value occupies a contiguous, fixed-size region of SLRU bytes.
1745 : : * (MultiXactMemberCtl separates flags from XIDs. NotifyCtl has
1746 : : * variable-length entries, no keys, and no random access. These unit tests
1747 : : * do not apply to them.)
1748 : : */
1749 : : void
1750 : : SlruPagePrecedesUnitTests(SlruDesc *ctl, int per_page)
1751 : : {
1752 : : /* Test first, middle and last entries of a page. */
1753 : : SlruPagePrecedesTestOffset(ctl, per_page, 0);
1754 : : SlruPagePrecedesTestOffset(ctl, per_page, per_page / 2);
1755 : : SlruPagePrecedesTestOffset(ctl, per_page, per_page - 1);
1756 : : }
1757 : : #endif
1758 : :
1759 : : /*
1760 : : * SlruScanDirectory callback
1761 : : * This callback reports true if there's any segment wholly prior to the
1762 : : * one containing the page passed as "data".
1763 : : */
1764 : : bool
1765 : 931543 : SlruScanDirCbReportPresence(SlruDesc *ctl, char *filename, int64 segpage,
1766 : : void *data)
1767 : : {
1768 : 931543 : int64 cutoffPage = *(int64 *) data;
1769 : :
1770 [ + + ]: 931543 : if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
1771 : 95 : return true; /* found one; don't iterate any more */
1772 : :
1773 : 931448 : return false; /* keep going */
1774 : : }
1775 : :
1776 : : /*
1777 : : * SlruScanDirectory callback.
1778 : : * This callback deletes segments prior to the one passed in as "data".
1779 : : */
1780 : : static bool
1781 : 207444 : SlruScanDirCbDeleteCutoff(SlruDesc *ctl, char *filename, int64 segpage,
1782 : : void *data)
1783 : : {
1784 : 207444 : int64 cutoffPage = *(int64 *) data;
1785 : :
1786 [ + + ]: 207444 : if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
1787 : 141984 : SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
1788 : :
1789 : 207444 : return false; /* keep going */
1790 : : }
1791 : :
1792 : : /*
1793 : : * SlruScanDirectory callback.
1794 : : * This callback deletes all segments.
1795 : : */
1796 : : bool
1797 : 8 : SlruScanDirCbDeleteAll(SlruDesc *ctl, char *filename, int64 segpage, void *data)
1798 : : {
1799 : 8 : SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
1800 : :
1801 : 8 : return false; /* keep going */
1802 : : }
1803 : :
1804 : : /*
1805 : : * An internal function used by SlruScanDirectory().
1806 : : *
1807 : : * Returns true if a file with a name of a given length may be a correct
1808 : : * SLRU segment.
1809 : : */
1810 : : static inline bool
1811 : 1151915 : SlruCorrectSegmentFilenameLength(SlruDesc *ctl, size_t len)
1812 : : {
1813 [ + + ]: 1151915 : if (ctl->options.long_segment_names)
1814 : 2507 : return (len == 15); /* see SlruFileName() */
1815 : : else
1816 : :
1817 : : /*
1818 : : * Commit 638cf09e76d allowed 5-character lengths. Later commit
1819 : : * 73c986adde5 allowed 6-character length.
1820 : : *
1821 : : * Note: There is an ongoing plan to migrate all SLRUs to 64-bit page
1822 : : * numbers, and the corresponding 15-character file names, which may
1823 : : * eventually deprecate the support for 4, 5, and 6-character names.
1824 : : */
1825 [ + + + - : 1149408 : return (len == 4 || len == 5 || len == 6);
- + ]
1826 : : }
1827 : :
1828 : : /*
1829 : : * Scan the SimpleLru directory and apply a callback to each file found in it.
1830 : : *
1831 : : * If the callback returns true, the scan is stopped. The last return value
1832 : : * from the callback is returned.
1833 : : *
1834 : : * The callback receives the following arguments: 1. the SlruCtl struct for the
1835 : : * slru being truncated; 2. the filename being considered; 3. the page number
1836 : : * for the first page of that file; 4. a pointer to the opaque data given to us
1837 : : * by the caller.
1838 : : *
1839 : : * Note that the ordering in which the directory is scanned is not guaranteed.
1840 : : *
1841 : : * Note that no locking is applied.
1842 : : */
1843 : : bool
1844 : 6525 : SlruScanDirectory(SlruDesc *ctl, SlruScanCallback callback, void *data)
1845 : : {
1846 : 6525 : bool retval = false;
1847 : : DIR *cldir;
1848 : : struct dirent *clde;
1849 : : int64 segno;
1850 : : int64 segpage;
1851 : :
1852 : 6525 : cldir = AllocateDir(ctl->options.Dir);
1853 [ + + ]: 1158345 : while ((clde = ReadDir(cldir, ctl->options.Dir)) != NULL)
1854 : : {
1855 : : size_t len;
1856 : :
1857 : 1151915 : len = strlen(clde->d_name);
1858 : :
1859 [ + + ]: 1151915 : if (SlruCorrectSegmentFilenameLength(ctl, len) &&
1860 [ + - ]: 1138995 : strspn(clde->d_name, "0123456789ABCDEF") == len)
1861 : : {
1862 : 1138995 : segno = strtoi64(clde->d_name, NULL, 16);
1863 : 1138995 : segpage = segno * SLRU_PAGES_PER_SEGMENT;
1864 : :
1865 [ + + ]: 1138995 : elog(DEBUG2, "SlruScanDirectory invoking callback on %s/%s",
1866 : : ctl->options.Dir, clde->d_name);
1867 : 1138995 : retval = callback(ctl, clde->d_name, segpage, data);
1868 [ + + ]: 1138995 : if (retval)
1869 : 95 : break;
1870 : : }
1871 : : }
1872 : 6525 : FreeDir(cldir);
1873 : :
1874 : 6525 : return retval;
1875 : : }
1876 : :
1877 : : /*
1878 : : * Individual SLRUs (clog, ...) have to provide a sync.c handler function so
1879 : : * that they can provide the correct "SlruCtl" (otherwise we don't know how to
1880 : : * build the path), but they just forward to this common implementation that
1881 : : * performs the fsync.
1882 : : */
1883 : : int
1884 : 2 : SlruSyncFileTag(SlruDesc *ctl, const FileTag *ftag, char *path)
1885 : : {
1886 : : int fd;
1887 : : int save_errno;
1888 : : int result;
1889 : :
1890 : 2 : SlruFileName(ctl, path, ftag->segno);
1891 : :
1892 : 2 : fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
1893 [ - + ]: 2 : if (fd < 0)
1894 : 0 : return -1;
1895 : :
1896 : 2 : pgstat_report_wait_start(WAIT_EVENT_SLRU_FLUSH_SYNC);
1897 : 2 : result = pg_fsync(fd);
1898 : 2 : pgstat_report_wait_end();
1899 : 2 : save_errno = errno;
1900 : :
1901 : 2 : CloseTransientFile(fd);
1902 : :
1903 : 2 : errno = save_errno;
1904 : 2 : return result;
1905 : : }
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