Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * gistvacuum.c
4 : * vacuuming routines for the postgres GiST index access method.
5 : *
6 : *
7 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
8 : * Portions Copyright (c) 1994, Regents of the University of California
9 : *
10 : * IDENTIFICATION
11 : * src/backend/access/gist/gistvacuum.c
12 : *
13 : *-------------------------------------------------------------------------
14 : */
15 : #include "postgres.h"
16 :
17 : #include "access/genam.h"
18 : #include "access/gist_private.h"
19 : #include "access/transam.h"
20 : #include "commands/vacuum.h"
21 : #include "lib/integerset.h"
22 : #include "miscadmin.h"
23 : #include "storage/indexfsm.h"
24 : #include "storage/lmgr.h"
25 : #include "storage/read_stream.h"
26 : #include "utils/memutils.h"
27 :
28 : /* Working state needed by gistbulkdelete */
29 : typedef struct
30 : {
31 : IndexVacuumInfo *info;
32 : IndexBulkDeleteResult *stats;
33 : IndexBulkDeleteCallback callback;
34 : void *callback_state;
35 : GistNSN startNSN;
36 :
37 : /*
38 : * These are used to memorize all internal and empty leaf pages. They are
39 : * used for deleting all the empty pages.
40 : */
41 : IntegerSet *internal_page_set;
42 : IntegerSet *empty_leaf_set;
43 : MemoryContext page_set_context;
44 : } GistVacState;
45 :
46 : static void gistvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
47 : IndexBulkDeleteCallback callback, void *callback_state);
48 : static void gistvacuumpage(GistVacState *vstate, Buffer buffer);
49 : static void gistvacuum_delete_empty_pages(IndexVacuumInfo *info,
50 : GistVacState *vstate);
51 : static bool gistdeletepage(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
52 : Buffer parentBuffer, OffsetNumber downlink,
53 : Buffer leafBuffer);
54 :
55 : /*
56 : * VACUUM bulkdelete stage: remove index entries.
57 : */
58 : IndexBulkDeleteResult *
59 42 : gistbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
60 : IndexBulkDeleteCallback callback, void *callback_state)
61 : {
62 : /* allocate stats if first time through, else re-use existing struct */
63 42 : if (stats == NULL)
64 42 : stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
65 :
66 42 : gistvacuumscan(info, stats, callback, callback_state);
67 :
68 42 : return stats;
69 : }
70 :
71 : /*
72 : * VACUUM cleanup stage: delete empty pages, and update index statistics.
73 : */
74 : IndexBulkDeleteResult *
75 88 : gistvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
76 : {
77 : /* No-op in ANALYZE ONLY mode */
78 88 : if (info->analyze_only)
79 20 : return stats;
80 :
81 : /*
82 : * If gistbulkdelete was called, we need not do anything, just return the
83 : * stats from the latest gistbulkdelete call. If it wasn't called, we
84 : * still need to do a pass over the index, to obtain index statistics.
85 : */
86 68 : if (stats == NULL)
87 : {
88 44 : stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
89 44 : gistvacuumscan(info, stats, NULL, NULL);
90 : }
91 :
92 : /*
93 : * It's quite possible for us to be fooled by concurrent page splits into
94 : * double-counting some index tuples, so disbelieve any total that exceeds
95 : * the underlying heap's count ... if we know that accurately. Otherwise
96 : * this might just make matters worse.
97 : */
98 68 : if (!info->estimated_count)
99 : {
100 68 : if (stats->num_index_tuples > info->num_heap_tuples)
101 0 : stats->num_index_tuples = info->num_heap_tuples;
102 : }
103 :
104 68 : return stats;
105 : }
106 :
107 : /*
108 : * gistvacuumscan --- scan the index for VACUUMing purposes
109 : *
110 : * This scans the index for leaf tuples that are deletable according to the
111 : * vacuum callback, and updates the stats. Both btbulkdelete and
112 : * btvacuumcleanup invoke this (the latter only if no btbulkdelete call
113 : * occurred).
114 : *
115 : * This also makes note of any empty leaf pages, as well as all internal
116 : * pages while looping over all index pages. After scanning all the pages, we
117 : * remove the empty pages so that they can be reused. Any deleted pages are
118 : * added directly to the free space map. (They should've been added there
119 : * when they were originally deleted, already, but it's possible that the FSM
120 : * was lost at a crash, for example.)
121 : *
122 : * The caller is responsible for initially allocating/zeroing a stats struct.
123 : */
124 : static void
125 86 : gistvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
126 : IndexBulkDeleteCallback callback, void *callback_state)
127 : {
128 86 : Relation rel = info->index;
129 : GistVacState vstate;
130 : BlockNumber num_pages;
131 : bool needLock;
132 : MemoryContext oldctx;
133 : BlockRangeReadStreamPrivate p;
134 86 : ReadStream *stream = NULL;
135 :
136 : /*
137 : * Reset fields that track information about the entire index now. This
138 : * avoids double-counting in the case where a single VACUUM command
139 : * requires multiple scans of the index.
140 : *
141 : * Avoid resetting the tuples_removed and pages_newly_deleted fields here,
142 : * since they track information about the VACUUM command, and so must last
143 : * across each call to gistvacuumscan().
144 : *
145 : * (Note that pages_free is treated as state about the whole index, not
146 : * the current VACUUM. This is appropriate because RecordFreeIndexPage()
147 : * calls are idempotent, and get repeated for the same deleted pages in
148 : * some scenarios. The point for us is to track the number of recyclable
149 : * pages in the index at the end of the VACUUM command.)
150 : */
151 86 : stats->num_pages = 0;
152 86 : stats->estimated_count = false;
153 86 : stats->num_index_tuples = 0;
154 86 : stats->pages_deleted = 0;
155 86 : stats->pages_free = 0;
156 :
157 : /*
158 : * Create the integer sets to remember all the internal and the empty leaf
159 : * pages in page_set_context. Internally, the integer set will remember
160 : * this context so that the subsequent allocations for these integer sets
161 : * will be done from the same context.
162 : *
163 : * XXX the allocation sizes used below pre-date generation context's block
164 : * growing code. These values should likely be benchmarked and set to
165 : * more suitable values.
166 : */
167 86 : vstate.page_set_context = GenerationContextCreate(CurrentMemoryContext,
168 : "GiST VACUUM page set context",
169 : 16 * 1024,
170 : 16 * 1024,
171 : 16 * 1024);
172 86 : oldctx = MemoryContextSwitchTo(vstate.page_set_context);
173 86 : vstate.internal_page_set = intset_create();
174 86 : vstate.empty_leaf_set = intset_create();
175 86 : MemoryContextSwitchTo(oldctx);
176 :
177 : /* Set up info to pass down to gistvacuumpage */
178 86 : vstate.info = info;
179 86 : vstate.stats = stats;
180 86 : vstate.callback = callback;
181 86 : vstate.callback_state = callback_state;
182 86 : if (RelationNeedsWAL(rel))
183 86 : vstate.startNSN = GetInsertRecPtr();
184 : else
185 0 : vstate.startNSN = gistGetFakeLSN(rel);
186 :
187 : /*
188 : * The outer loop iterates over all index pages, in physical order (we
189 : * hope the kernel will cooperate in providing read-ahead for speed). It
190 : * is critical that we visit all leaf pages, including ones added after we
191 : * start the scan, else we might fail to delete some deletable tuples.
192 : * Hence, we must repeatedly check the relation length. We must acquire
193 : * the relation-extension lock while doing so to avoid a race condition:
194 : * if someone else is extending the relation, there is a window where
195 : * bufmgr/smgr have created a new all-zero page but it hasn't yet been
196 : * write-locked by gistNewBuffer(). If we manage to scan such a page
197 : * here, we'll improperly assume it can be recycled. Taking the lock
198 : * synchronizes things enough to prevent a problem: either num_pages won't
199 : * include the new page, or gistNewBuffer already has write lock on the
200 : * buffer and it will be fully initialized before we can examine it. (See
201 : * also vacuumlazy.c, which has the same issue.) Also, we need not worry
202 : * if a page is added immediately after we look; the page splitting code
203 : * already has write-lock on the left page before it adds a right page, so
204 : * we must already have processed any tuples due to be moved into such a
205 : * page.
206 : *
207 : * We can skip locking for new or temp relations, however, since no one
208 : * else could be accessing them.
209 : */
210 86 : needLock = !RELATION_IS_LOCAL(rel);
211 :
212 86 : p.current_blocknum = GIST_ROOT_BLKNO;
213 :
214 : /*
215 : * It is safe to use batchmode as block_range_read_stream_cb takes no
216 : * locks.
217 : */
218 86 : stream = read_stream_begin_relation(READ_STREAM_MAINTENANCE |
219 : READ_STREAM_FULL |
220 : READ_STREAM_USE_BATCHING,
221 : info->strategy,
222 : rel,
223 : MAIN_FORKNUM,
224 : block_range_read_stream_cb,
225 : &p,
226 : 0);
227 : for (;;)
228 : {
229 : /* Get the current relation length */
230 172 : if (needLock)
231 172 : LockRelationForExtension(rel, ExclusiveLock);
232 172 : num_pages = RelationGetNumberOfBlocks(rel);
233 172 : if (needLock)
234 172 : UnlockRelationForExtension(rel, ExclusiveLock);
235 :
236 : /* Quit if we've scanned the whole relation */
237 172 : if (p.current_blocknum >= num_pages)
238 86 : break;
239 :
240 86 : p.last_exclusive = num_pages;
241 :
242 : /* Iterate over pages, then loop back to recheck relation length */
243 : while (true)
244 2638 : {
245 : Buffer buf;
246 :
247 : /* call vacuum_delay_point while not holding any buffer lock */
248 2724 : vacuum_delay_point(false);
249 :
250 2724 : buf = read_stream_next_buffer(stream, NULL);
251 :
252 2724 : if (!BufferIsValid(buf))
253 86 : break;
254 :
255 2638 : gistvacuumpage(&vstate, buf);
256 : }
257 :
258 : /*
259 : * We have to reset the read stream to use it again. After returning
260 : * InvalidBuffer, the read stream API won't invoke our callback again
261 : * until the stream has been reset.
262 : */
263 86 : read_stream_reset(stream);
264 : }
265 :
266 86 : read_stream_end(stream);
267 :
268 : /*
269 : * If we found any recyclable pages (and recorded them in the FSM), then
270 : * forcibly update the upper-level FSM pages to ensure that searchers can
271 : * find them. It's possible that the pages were also found during
272 : * previous scans and so this is a waste of time, but it's cheap enough
273 : * relative to scanning the index that it shouldn't matter much, and
274 : * making sure that free pages are available sooner not later seems
275 : * worthwhile.
276 : *
277 : * Note that if no recyclable pages exist, we don't bother vacuuming the
278 : * FSM at all.
279 : */
280 86 : if (stats->pages_free > 0)
281 0 : IndexFreeSpaceMapVacuum(rel);
282 :
283 : /* update statistics */
284 86 : stats->num_pages = num_pages;
285 :
286 : /*
287 : * If we saw any empty pages, try to unlink them from the tree so that
288 : * they can be reused.
289 : */
290 86 : gistvacuum_delete_empty_pages(info, &vstate);
291 :
292 : /* we don't need the internal and empty page sets anymore */
293 86 : MemoryContextDelete(vstate.page_set_context);
294 86 : vstate.page_set_context = NULL;
295 86 : vstate.internal_page_set = NULL;
296 86 : vstate.empty_leaf_set = NULL;
297 86 : }
298 :
299 : /*
300 : * gistvacuumpage --- VACUUM one page
301 : *
302 : * This processes a single page for gistbulkdelete(). `buffer` contains the
303 : * page to process. In some cases we must go back and reexamine
304 : * previously-scanned pages; this routine recurses when necessary to handle
305 : * that case.
306 : */
307 : static void
308 2638 : gistvacuumpage(GistVacState *vstate, Buffer buffer)
309 : {
310 2638 : IndexVacuumInfo *info = vstate->info;
311 2638 : IndexBulkDeleteCallback callback = vstate->callback;
312 2638 : void *callback_state = vstate->callback_state;
313 2638 : Relation rel = info->index;
314 2638 : BlockNumber orig_blkno = BufferGetBlockNumber(buffer);
315 : Page page;
316 : BlockNumber recurse_to;
317 :
318 : /*
319 : * orig_blkno is the highest block number reached by the outer
320 : * gistvacuumscan() loop. This will be the same as blkno unless we are
321 : * recursing to reexamine a previous page.
322 : */
323 2638 : BlockNumber blkno = orig_blkno;
324 :
325 2638 : restart:
326 2638 : recurse_to = InvalidBlockNumber;
327 :
328 : /*
329 : * We are not going to stay here for a long time, aggressively grab an
330 : * exclusive lock.
331 : */
332 2638 : LockBuffer(buffer, GIST_EXCLUSIVE);
333 2638 : page = (Page) BufferGetPage(buffer);
334 :
335 2638 : if (gistPageRecyclable(page))
336 : {
337 : /* Okay to recycle this page */
338 0 : RecordFreeIndexPage(rel, blkno);
339 0 : vstate->stats->pages_deleted++;
340 0 : vstate->stats->pages_free++;
341 : }
342 2638 : else if (GistPageIsDeleted(page))
343 : {
344 : /* Already deleted, but can't recycle yet */
345 0 : vstate->stats->pages_deleted++;
346 : }
347 2638 : else if (GistPageIsLeaf(page))
348 : {
349 : OffsetNumber todelete[MaxOffsetNumber];
350 2584 : int ntodelete = 0;
351 : int nremain;
352 2584 : GISTPageOpaque opaque = GistPageGetOpaque(page);
353 2584 : OffsetNumber maxoff = PageGetMaxOffsetNumber(page);
354 :
355 : /*
356 : * Check whether we need to recurse back to earlier pages. What we
357 : * are concerned about is a page split that happened since we started
358 : * the vacuum scan. If the split moved some tuples to a lower page
359 : * then we might have missed 'em. If so, set up for tail recursion.
360 : *
361 : * This is similar to the checks we do during searches, when following
362 : * a downlink, but we don't need to jump to higher-numbered pages,
363 : * because we will process them later, anyway.
364 : */
365 5168 : if ((GistFollowRight(page) ||
366 2584 : vstate->startNSN < GistPageGetNSN(page)) &&
367 0 : (opaque->rightlink != InvalidBlockNumber) &&
368 0 : (opaque->rightlink < orig_blkno))
369 : {
370 0 : recurse_to = opaque->rightlink;
371 : }
372 :
373 : /*
374 : * Scan over all items to see which ones need to be deleted according
375 : * to the callback function.
376 : */
377 2584 : if (callback)
378 : {
379 : OffsetNumber off;
380 :
381 100694 : for (off = FirstOffsetNumber;
382 : off <= maxoff;
383 99860 : off = OffsetNumberNext(off))
384 : {
385 99860 : ItemId iid = PageGetItemId(page, off);
386 99860 : IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
387 :
388 99860 : if (callback(&(idxtuple->t_tid), callback_state))
389 77876 : todelete[ntodelete++] = off;
390 : }
391 : }
392 :
393 : /*
394 : * Apply any needed deletes. We issue just one WAL record per page,
395 : * so as to minimize WAL traffic.
396 : */
397 2584 : if (ntodelete > 0)
398 : {
399 816 : START_CRIT_SECTION();
400 :
401 816 : MarkBufferDirty(buffer);
402 :
403 816 : PageIndexMultiDelete(page, todelete, ntodelete);
404 816 : GistMarkTuplesDeleted(page);
405 :
406 816 : if (RelationNeedsWAL(rel))
407 816 : {
408 : XLogRecPtr recptr;
409 :
410 816 : recptr = gistXLogUpdate(buffer,
411 : todelete, ntodelete,
412 : NULL, 0, InvalidBuffer);
413 816 : PageSetLSN(page, recptr);
414 : }
415 : else
416 0 : PageSetLSN(page, gistGetFakeLSN(rel));
417 :
418 816 : END_CRIT_SECTION();
419 :
420 816 : vstate->stats->tuples_removed += ntodelete;
421 : /* must recompute maxoff */
422 816 : maxoff = PageGetMaxOffsetNumber(page);
423 : }
424 :
425 2584 : nremain = maxoff - FirstOffsetNumber + 1;
426 2584 : if (nremain == 0)
427 : {
428 : /*
429 : * The page is now completely empty. Remember its block number,
430 : * so that we will try to delete the page in the second stage.
431 : *
432 : * Skip this when recursing, because IntegerSet requires that the
433 : * values are added in ascending order. The next VACUUM will pick
434 : * it up.
435 : */
436 336 : if (blkno == orig_blkno)
437 336 : intset_add_member(vstate->empty_leaf_set, blkno);
438 : }
439 : else
440 2248 : vstate->stats->num_index_tuples += nremain;
441 : }
442 : else
443 : {
444 : /*
445 : * On an internal page, check for "invalid tuples", left behind by an
446 : * incomplete page split on PostgreSQL 9.0 or below. These are not
447 : * created by newer PostgreSQL versions, but unfortunately, there is
448 : * no version number anywhere in a GiST index, so we don't know
449 : * whether this index might still contain invalid tuples or not.
450 : */
451 54 : OffsetNumber maxoff = PageGetMaxOffsetNumber(page);
452 : OffsetNumber off;
453 :
454 2606 : for (off = FirstOffsetNumber;
455 : off <= maxoff;
456 2552 : off = OffsetNumberNext(off))
457 : {
458 2552 : ItemId iid = PageGetItemId(page, off);
459 2552 : IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
460 :
461 2552 : if (GistTupleIsInvalid(idxtuple))
462 0 : ereport(LOG,
463 : (errmsg("index \"%s\" contains an inner tuple marked as invalid",
464 : RelationGetRelationName(rel)),
465 : errdetail("This is caused by an incomplete page split at crash recovery before upgrading to PostgreSQL 9.1."),
466 : errhint("Please REINDEX it.")));
467 : }
468 :
469 : /*
470 : * Remember the block number of this page, so that we can revisit it
471 : * later in gistvacuum_delete_empty_pages(), when we search for
472 : * parents of empty leaf pages.
473 : */
474 54 : if (blkno == orig_blkno)
475 54 : intset_add_member(vstate->internal_page_set, blkno);
476 : }
477 :
478 2638 : UnlockReleaseBuffer(buffer);
479 :
480 : /*
481 : * This is really tail recursion, but if the compiler is too stupid to
482 : * optimize it as such, we'd eat an uncomfortably large amount of stack
483 : * space per recursion level (due to the deletable[] array). A failure is
484 : * improbable since the number of levels isn't likely to be large ... but
485 : * just in case, let's hand-optimize into a loop.
486 : */
487 2638 : if (recurse_to != InvalidBlockNumber)
488 : {
489 0 : blkno = recurse_to;
490 :
491 : /* check for vacuum delay while not holding any buffer lock */
492 0 : vacuum_delay_point(false);
493 :
494 0 : buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
495 : info->strategy);
496 0 : goto restart;
497 : }
498 2638 : }
499 :
500 : /*
501 : * Scan all internal pages, and try to delete their empty child pages.
502 : */
503 : static void
504 86 : gistvacuum_delete_empty_pages(IndexVacuumInfo *info, GistVacState *vstate)
505 : {
506 86 : Relation rel = info->index;
507 : BlockNumber empty_pages_remaining;
508 : uint64 blkno;
509 :
510 : /*
511 : * Rescan all inner pages to find those that have empty child pages.
512 : */
513 86 : empty_pages_remaining = intset_num_entries(vstate->empty_leaf_set);
514 86 : intset_begin_iterate(vstate->internal_page_set);
515 106 : while (empty_pages_remaining > 0 &&
516 16 : intset_iterate_next(vstate->internal_page_set, &blkno))
517 : {
518 : Buffer buffer;
519 : Page page;
520 : OffsetNumber off,
521 : maxoff;
522 : OffsetNumber todelete[MaxOffsetNumber];
523 : BlockNumber leafs_to_delete[MaxOffsetNumber];
524 : int ntodelete;
525 : int deleted;
526 :
527 4 : buffer = ReadBufferExtended(rel, MAIN_FORKNUM, (BlockNumber) blkno,
528 : RBM_NORMAL, info->strategy);
529 :
530 4 : LockBuffer(buffer, GIST_SHARE);
531 4 : page = (Page) BufferGetPage(buffer);
532 :
533 4 : if (PageIsNew(page) || GistPageIsDeleted(page) || GistPageIsLeaf(page))
534 : {
535 : /*
536 : * This page was an internal page earlier, but now it's something
537 : * else. Shouldn't happen...
538 : */
539 : Assert(false);
540 0 : UnlockReleaseBuffer(buffer);
541 0 : continue;
542 : }
543 :
544 : /*
545 : * Scan all the downlinks, and see if any of them point to empty leaf
546 : * pages.
547 : */
548 4 : maxoff = PageGetMaxOffsetNumber(page);
549 4 : ntodelete = 0;
550 656 : for (off = FirstOffsetNumber;
551 652 : off <= maxoff && ntodelete < maxoff - 1;
552 652 : off = OffsetNumberNext(off))
553 : {
554 652 : ItemId iid = PageGetItemId(page, off);
555 652 : IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
556 : BlockNumber leafblk;
557 :
558 652 : leafblk = ItemPointerGetBlockNumber(&(idxtuple->t_tid));
559 652 : if (intset_is_member(vstate->empty_leaf_set, leafblk))
560 : {
561 324 : leafs_to_delete[ntodelete] = leafblk;
562 324 : todelete[ntodelete++] = off;
563 : }
564 : }
565 :
566 : /*
567 : * In order to avoid deadlock, child page must be locked before
568 : * parent, so we must release the lock on the parent, lock the child,
569 : * and then re-acquire the lock the parent. (And we wouldn't want to
570 : * do I/O, while holding a lock, anyway.)
571 : *
572 : * At the instant that we're not holding a lock on the parent, the
573 : * downlink might get moved by a concurrent insert, so we must
574 : * re-check that it still points to the same child page after we have
575 : * acquired both locks. Also, another backend might have inserted a
576 : * tuple to the page, so that it is no longer empty. gistdeletepage()
577 : * re-checks all these conditions.
578 : */
579 4 : LockBuffer(buffer, GIST_UNLOCK);
580 :
581 4 : deleted = 0;
582 328 : for (int i = 0; i < ntodelete; i++)
583 : {
584 : Buffer leafbuf;
585 :
586 : /*
587 : * Don't remove the last downlink from the parent. That would
588 : * confuse the insertion code.
589 : */
590 324 : if (PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
591 0 : break;
592 :
593 324 : leafbuf = ReadBufferExtended(rel, MAIN_FORKNUM, leafs_to_delete[i],
594 : RBM_NORMAL, info->strategy);
595 324 : LockBuffer(leafbuf, GIST_EXCLUSIVE);
596 324 : gistcheckpage(rel, leafbuf);
597 :
598 324 : LockBuffer(buffer, GIST_EXCLUSIVE);
599 324 : if (gistdeletepage(info, vstate->stats,
600 324 : buffer, todelete[i] - deleted,
601 : leafbuf))
602 324 : deleted++;
603 324 : LockBuffer(buffer, GIST_UNLOCK);
604 :
605 324 : UnlockReleaseBuffer(leafbuf);
606 : }
607 :
608 4 : ReleaseBuffer(buffer);
609 :
610 : /*
611 : * We can stop the scan as soon as we have seen the downlinks, even if
612 : * we were not able to remove them all.
613 : */
614 4 : empty_pages_remaining -= ntodelete;
615 : }
616 86 : }
617 :
618 : /*
619 : * gistdeletepage takes a leaf page, and its parent, and tries to delete the
620 : * leaf. Both pages must be locked.
621 : *
622 : * Even if the page was empty when we first saw it, a concurrent inserter might
623 : * have added a tuple to it since. Similarly, the downlink might have moved.
624 : * We re-check all the conditions, to make sure the page is still deletable,
625 : * before modifying anything.
626 : *
627 : * Returns true, if the page was deleted, and false if a concurrent update
628 : * prevented it.
629 : */
630 : static bool
631 324 : gistdeletepage(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
632 : Buffer parentBuffer, OffsetNumber downlink,
633 : Buffer leafBuffer)
634 : {
635 324 : Page parentPage = BufferGetPage(parentBuffer);
636 324 : Page leafPage = BufferGetPage(leafBuffer);
637 : ItemId iid;
638 : IndexTuple idxtuple;
639 : XLogRecPtr recptr;
640 : FullTransactionId txid;
641 :
642 : /*
643 : * Check that the leaf is still empty and deletable.
644 : */
645 324 : if (!GistPageIsLeaf(leafPage))
646 : {
647 : /* a leaf page should never become a non-leaf page */
648 : Assert(false);
649 0 : return false;
650 : }
651 :
652 324 : if (GistFollowRight(leafPage))
653 0 : return false; /* don't mess with a concurrent page split */
654 :
655 324 : if (PageGetMaxOffsetNumber(leafPage) != InvalidOffsetNumber)
656 0 : return false; /* not empty anymore */
657 :
658 : /*
659 : * Ok, the leaf is deletable. Is the downlink in the parent page still
660 : * valid? It might have been moved by a concurrent insert. We could try
661 : * to re-find it by scanning the page again, possibly moving right if the
662 : * was split. But for now, let's keep it simple and just give up. The
663 : * next VACUUM will pick it up.
664 : */
665 324 : if (PageIsNew(parentPage) || GistPageIsDeleted(parentPage) ||
666 324 : GistPageIsLeaf(parentPage))
667 : {
668 : /* shouldn't happen, internal pages are never deleted */
669 : Assert(false);
670 0 : return false;
671 : }
672 :
673 324 : if (PageGetMaxOffsetNumber(parentPage) < downlink
674 324 : || PageGetMaxOffsetNumber(parentPage) <= FirstOffsetNumber)
675 0 : return false;
676 :
677 324 : iid = PageGetItemId(parentPage, downlink);
678 324 : idxtuple = (IndexTuple) PageGetItem(parentPage, iid);
679 648 : if (BufferGetBlockNumber(leafBuffer) !=
680 324 : ItemPointerGetBlockNumber(&(idxtuple->t_tid)))
681 0 : return false;
682 :
683 : /*
684 : * All good, proceed with the deletion.
685 : *
686 : * The page cannot be immediately recycled, because in-progress scans that
687 : * saw the downlink might still visit it. Mark the page with the current
688 : * next-XID counter, so that we know when it can be recycled. Once that
689 : * XID becomes older than GlobalXmin, we know that all scans that are
690 : * currently in progress must have ended. (That's much more conservative
691 : * than needed, but let's keep it safe and simple.)
692 : */
693 324 : txid = ReadNextFullTransactionId();
694 :
695 324 : START_CRIT_SECTION();
696 :
697 : /* mark the page as deleted */
698 324 : MarkBufferDirty(leafBuffer);
699 324 : GistPageSetDeleted(leafPage, txid);
700 324 : stats->pages_newly_deleted++;
701 324 : stats->pages_deleted++;
702 :
703 : /* remove the downlink from the parent */
704 324 : MarkBufferDirty(parentBuffer);
705 324 : PageIndexTupleDelete(parentPage, downlink);
706 :
707 324 : if (RelationNeedsWAL(info->index))
708 324 : recptr = gistXLogPageDelete(leafBuffer, txid, parentBuffer, downlink);
709 : else
710 0 : recptr = gistGetFakeLSN(info->index);
711 324 : PageSetLSN(parentPage, recptr);
712 324 : PageSetLSN(leafPage, recptr);
713 :
714 324 : END_CRIT_SECTION();
715 :
716 324 : return true;
717 : }
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