Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * nbtpage.c
4 : * BTree-specific page management code for the Postgres btree access
5 : * method.
6 : *
7 : * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
8 : * Portions Copyright (c) 1994, Regents of the University of California
9 : *
10 : *
11 : * IDENTIFICATION
12 : * src/backend/access/nbtree/nbtpage.c
13 : *
14 : * NOTES
15 : * Postgres btree pages look like ordinary relation pages. The opaque
16 : * data at high addresses includes pointers to left and right siblings
17 : * and flag data describing page state. The first page in a btree, page
18 : * zero, is special -- it stores meta-information describing the tree.
19 : * Pages one and higher store the actual tree data.
20 : *
21 : *-------------------------------------------------------------------------
22 : */
23 : #include "postgres.h"
24 :
25 : #include "access/nbtree.h"
26 : #include "access/nbtxlog.h"
27 : #include "access/transam.h"
28 : #include "access/xlog.h"
29 : #include "access/xloginsert.h"
30 : #include "miscadmin.h"
31 : #include "storage/indexfsm.h"
32 : #include "storage/lmgr.h"
33 : #include "storage/predicate.h"
34 : #include "utils/snapmgr.h"
35 :
36 : static bool _bt_mark_page_halfdead(Relation rel, Buffer buf, BTStack stack);
37 : static bool _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf,
38 : bool *rightsib_empty);
39 : static bool _bt_lock_branch_parent(Relation rel, BlockNumber child,
40 : BTStack stack, Buffer *topparent, OffsetNumber *topoff,
41 : BlockNumber *target, BlockNumber *rightsib);
42 : static void _bt_log_reuse_page(Relation rel, BlockNumber blkno,
43 : TransactionId latestRemovedXid);
44 :
45 : /*
46 : * _bt_initmetapage() -- Fill a page buffer with a correct metapage image
47 : */
48 : void
49 1433 : _bt_initmetapage(Page page, BlockNumber rootbknum, uint32 level)
50 : {
51 : BTMetaPageData *metad;
52 : BTPageOpaque metaopaque;
53 :
54 1433 : _bt_pageinit(page, BLCKSZ);
55 :
56 1433 : metad = BTPageGetMeta(page);
57 1433 : metad->btm_magic = BTREE_MAGIC;
58 1433 : metad->btm_version = BTREE_VERSION;
59 1433 : metad->btm_root = rootbknum;
60 1433 : metad->btm_level = level;
61 1433 : metad->btm_fastroot = rootbknum;
62 1433 : metad->btm_fastlevel = level;
63 :
64 1433 : metaopaque = (BTPageOpaque) PageGetSpecialPointer(page);
65 1433 : metaopaque->btpo_flags = BTP_META;
66 :
67 : /*
68 : * Set pd_lower just past the end of the metadata. This is not essential
69 : * but it makes the page look compressible to xlog.c.
70 : */
71 1433 : ((PageHeader) page)->pd_lower =
72 1433 : ((char *) metad + sizeof(BTMetaPageData)) - (char *) page;
73 1433 : }
74 :
75 : /*
76 : * _bt_getroot() -- Get the root page of the btree.
77 : *
78 : * Since the root page can move around the btree file, we have to read
79 : * its location from the metadata page, and then read the root page
80 : * itself. If no root page exists yet, we have to create one. The
81 : * standard class of race conditions exists here; I think I covered
82 : * them all in the Hopi Indian rain dance of lock requests below.
83 : *
84 : * The access type parameter (BT_READ or BT_WRITE) controls whether
85 : * a new root page will be created or not. If access = BT_READ,
86 : * and no root page exists, we just return InvalidBuffer. For
87 : * BT_WRITE, we try to create the root page if it doesn't exist.
88 : * NOTE that the returned root page will have only a read lock set
89 : * on it even if access = BT_WRITE!
90 : *
91 : * The returned page is not necessarily the true root --- it could be
92 : * a "fast root" (a page that is alone in its level due to deletions).
93 : * Also, if the root page is split while we are "in flight" to it,
94 : * what we will return is the old root, which is now just the leftmost
95 : * page on a probably-not-very-wide level. For most purposes this is
96 : * as good as or better than the true root, so we do not bother to
97 : * insist on finding the true root. We do, however, guarantee to
98 : * return a live (not deleted or half-dead) page.
99 : *
100 : * On successful return, the root page is pinned and read-locked.
101 : * The metadata page is not locked or pinned on exit.
102 : */
103 : Buffer
104 593576 : _bt_getroot(Relation rel, int access)
105 : {
106 : Buffer metabuf;
107 : Page metapg;
108 : BTPageOpaque metaopaque;
109 : Buffer rootbuf;
110 : Page rootpage;
111 : BTPageOpaque rootopaque;
112 : BlockNumber rootblkno;
113 : uint32 rootlevel;
114 : BTMetaPageData *metad;
115 :
116 : /*
117 : * Try to use previously-cached metapage data to find the root. This
118 : * normally saves one buffer access per index search, which is a very
119 : * helpful savings in bufmgr traffic and hence contention.
120 : */
121 593576 : if (rel->rd_amcache != NULL)
122 : {
123 569772 : metad = (BTMetaPageData *) rel->rd_amcache;
124 : /* We shouldn't have cached it if any of these fail */
125 569772 : Assert(metad->btm_magic == BTREE_MAGIC);
126 569772 : Assert(metad->btm_version == BTREE_VERSION);
127 569772 : Assert(metad->btm_root != P_NONE);
128 :
129 569772 : rootblkno = metad->btm_fastroot;
130 569772 : Assert(rootblkno != P_NONE);
131 569772 : rootlevel = metad->btm_fastlevel;
132 :
133 569772 : rootbuf = _bt_getbuf(rel, rootblkno, BT_READ);
134 569772 : rootpage = BufferGetPage(rootbuf);
135 569772 : rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
136 :
137 : /*
138 : * Since the cache might be stale, we check the page more carefully
139 : * here than normal. We *must* check that it's not deleted. If it's
140 : * not alone on its level, then we reject too --- this may be overly
141 : * paranoid but better safe than sorry. Note we don't check P_ISROOT,
142 : * because that's not set in a "fast root".
143 : */
144 1139544 : if (!P_IGNORE(rootopaque) &&
145 1139544 : rootopaque->btpo.level == rootlevel &&
146 1139544 : P_LEFTMOST(rootopaque) &&
147 569772 : P_RIGHTMOST(rootopaque))
148 : {
149 : /* OK, accept cached page as the root */
150 569727 : return rootbuf;
151 : }
152 45 : _bt_relbuf(rel, rootbuf);
153 : /* Cache is stale, throw it away */
154 45 : if (rel->rd_amcache)
155 45 : pfree(rel->rd_amcache);
156 45 : rel->rd_amcache = NULL;
157 : }
158 :
159 23849 : metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
160 23849 : metapg = BufferGetPage(metabuf);
161 23849 : metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg);
162 23849 : metad = BTPageGetMeta(metapg);
163 :
164 : /* sanity-check the metapage */
165 47698 : if (!(metaopaque->btpo_flags & BTP_META) ||
166 23849 : metad->btm_magic != BTREE_MAGIC)
167 0 : ereport(ERROR,
168 : (errcode(ERRCODE_INDEX_CORRUPTED),
169 : errmsg("index \"%s\" is not a btree",
170 : RelationGetRelationName(rel))));
171 :
172 23849 : if (metad->btm_version != BTREE_VERSION)
173 0 : ereport(ERROR,
174 : (errcode(ERRCODE_INDEX_CORRUPTED),
175 : errmsg("version mismatch in index \"%s\": file version %d, code version %d",
176 : RelationGetRelationName(rel),
177 : metad->btm_version, BTREE_VERSION)));
178 :
179 : /* if no root page initialized yet, do it */
180 23849 : if (metad->btm_root == P_NONE)
181 : {
182 : /* If access = BT_READ, caller doesn't want us to create root yet */
183 12103 : if (access == BT_READ)
184 : {
185 11804 : _bt_relbuf(rel, metabuf);
186 11804 : return InvalidBuffer;
187 : }
188 :
189 : /* trade in our read lock for a write lock */
190 299 : LockBuffer(metabuf, BUFFER_LOCK_UNLOCK);
191 299 : LockBuffer(metabuf, BT_WRITE);
192 :
193 : /*
194 : * Race condition: if someone else initialized the metadata between
195 : * the time we released the read lock and acquired the write lock, we
196 : * must avoid doing it again.
197 : */
198 299 : if (metad->btm_root != P_NONE)
199 : {
200 : /*
201 : * Metadata initialized by someone else. In order to guarantee no
202 : * deadlocks, we have to release the metadata page and start all
203 : * over again. (Is that really true? But it's hardly worth trying
204 : * to optimize this case.)
205 : */
206 0 : _bt_relbuf(rel, metabuf);
207 0 : return _bt_getroot(rel, access);
208 : }
209 :
210 : /*
211 : * Get, initialize, write, and leave a lock of the appropriate type on
212 : * the new root page. Since this is the first page in the tree, it's
213 : * a leaf as well as the root.
214 : */
215 299 : rootbuf = _bt_getbuf(rel, P_NEW, BT_WRITE);
216 299 : rootblkno = BufferGetBlockNumber(rootbuf);
217 299 : rootpage = BufferGetPage(rootbuf);
218 299 : rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
219 299 : rootopaque->btpo_prev = rootopaque->btpo_next = P_NONE;
220 299 : rootopaque->btpo_flags = (BTP_LEAF | BTP_ROOT);
221 299 : rootopaque->btpo.level = 0;
222 299 : rootopaque->btpo_cycleid = 0;
223 :
224 : /* NO ELOG(ERROR) till meta is updated */
225 299 : START_CRIT_SECTION();
226 :
227 299 : metad->btm_root = rootblkno;
228 299 : metad->btm_level = 0;
229 299 : metad->btm_fastroot = rootblkno;
230 299 : metad->btm_fastlevel = 0;
231 :
232 299 : MarkBufferDirty(rootbuf);
233 299 : MarkBufferDirty(metabuf);
234 :
235 : /* XLOG stuff */
236 299 : if (RelationNeedsWAL(rel))
237 : {
238 : xl_btree_newroot xlrec;
239 : XLogRecPtr recptr;
240 : xl_btree_metadata md;
241 :
242 250 : XLogBeginInsert();
243 250 : XLogRegisterBuffer(0, rootbuf, REGBUF_WILL_INIT);
244 250 : XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT);
245 :
246 250 : md.root = rootblkno;
247 250 : md.level = 0;
248 250 : md.fastroot = rootblkno;
249 250 : md.fastlevel = 0;
250 :
251 250 : XLogRegisterBufData(2, (char *) &md, sizeof(xl_btree_metadata));
252 :
253 250 : xlrec.rootblk = rootblkno;
254 250 : xlrec.level = 0;
255 :
256 250 : XLogRegisterData((char *) &xlrec, SizeOfBtreeNewroot);
257 :
258 250 : recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_NEWROOT);
259 :
260 250 : PageSetLSN(rootpage, recptr);
261 250 : PageSetLSN(metapg, recptr);
262 : }
263 :
264 299 : END_CRIT_SECTION();
265 :
266 : /*
267 : * swap root write lock for read lock. There is no danger of anyone
268 : * else accessing the new root page while it's unlocked, since no one
269 : * else knows where it is yet.
270 : */
271 299 : LockBuffer(rootbuf, BUFFER_LOCK_UNLOCK);
272 299 : LockBuffer(rootbuf, BT_READ);
273 :
274 : /* okay, metadata is correct, release lock on it */
275 299 : _bt_relbuf(rel, metabuf);
276 : }
277 : else
278 : {
279 11746 : rootblkno = metad->btm_fastroot;
280 11746 : Assert(rootblkno != P_NONE);
281 11746 : rootlevel = metad->btm_fastlevel;
282 :
283 : /*
284 : * Cache the metapage data for next time
285 : */
286 11746 : rel->rd_amcache = MemoryContextAlloc(rel->rd_indexcxt,
287 : sizeof(BTMetaPageData));
288 11746 : memcpy(rel->rd_amcache, metad, sizeof(BTMetaPageData));
289 :
290 : /*
291 : * We are done with the metapage; arrange to release it via first
292 : * _bt_relandgetbuf call
293 : */
294 11746 : rootbuf = metabuf;
295 :
296 : for (;;)
297 : {
298 11746 : rootbuf = _bt_relandgetbuf(rel, rootbuf, rootblkno, BT_READ);
299 11746 : rootpage = BufferGetPage(rootbuf);
300 11746 : rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
301 :
302 11746 : if (!P_IGNORE(rootopaque))
303 11746 : break;
304 :
305 : /* it's dead, Jim. step right one page */
306 0 : if (P_RIGHTMOST(rootopaque))
307 0 : elog(ERROR, "no live root page found in index \"%s\"",
308 : RelationGetRelationName(rel));
309 0 : rootblkno = rootopaque->btpo_next;
310 0 : }
311 :
312 : /* Note: can't check btpo.level on deleted pages */
313 11746 : if (rootopaque->btpo.level != rootlevel)
314 0 : elog(ERROR, "root page %u of index \"%s\" has level %u, expected %u",
315 : rootblkno, RelationGetRelationName(rel),
316 : rootopaque->btpo.level, rootlevel);
317 : }
318 :
319 : /*
320 : * By here, we have a pin and read lock on the root page, and no lock set
321 : * on the metadata page. Return the root page's buffer.
322 : */
323 12045 : return rootbuf;
324 : }
325 :
326 : /*
327 : * _bt_gettrueroot() -- Get the true root page of the btree.
328 : *
329 : * This is the same as the BT_READ case of _bt_getroot(), except
330 : * we follow the true-root link not the fast-root link.
331 : *
332 : * By the time we acquire lock on the root page, it might have been split and
333 : * not be the true root anymore. This is okay for the present uses of this
334 : * routine; we only really need to be able to move up at least one tree level
335 : * from whatever non-root page we were at. If we ever do need to lock the
336 : * one true root page, we could loop here, re-reading the metapage on each
337 : * failure. (Note that it wouldn't do to hold the lock on the metapage while
338 : * moving to the root --- that'd deadlock against any concurrent root split.)
339 : */
340 : Buffer
341 0 : _bt_gettrueroot(Relation rel)
342 : {
343 : Buffer metabuf;
344 : Page metapg;
345 : BTPageOpaque metaopaque;
346 : Buffer rootbuf;
347 : Page rootpage;
348 : BTPageOpaque rootopaque;
349 : BlockNumber rootblkno;
350 : uint32 rootlevel;
351 : BTMetaPageData *metad;
352 :
353 : /*
354 : * We don't try to use cached metapage data here, since (a) this path is
355 : * not performance-critical, and (b) if we are here it suggests our cache
356 : * is out-of-date anyway. In light of point (b), it's probably safest to
357 : * actively flush any cached metapage info.
358 : */
359 0 : if (rel->rd_amcache)
360 0 : pfree(rel->rd_amcache);
361 0 : rel->rd_amcache = NULL;
362 :
363 0 : metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
364 0 : metapg = BufferGetPage(metabuf);
365 0 : metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg);
366 0 : metad = BTPageGetMeta(metapg);
367 :
368 0 : if (!(metaopaque->btpo_flags & BTP_META) ||
369 0 : metad->btm_magic != BTREE_MAGIC)
370 0 : ereport(ERROR,
371 : (errcode(ERRCODE_INDEX_CORRUPTED),
372 : errmsg("index \"%s\" is not a btree",
373 : RelationGetRelationName(rel))));
374 :
375 0 : if (metad->btm_version != BTREE_VERSION)
376 0 : ereport(ERROR,
377 : (errcode(ERRCODE_INDEX_CORRUPTED),
378 : errmsg("version mismatch in index \"%s\": file version %d, code version %d",
379 : RelationGetRelationName(rel),
380 : metad->btm_version, BTREE_VERSION)));
381 :
382 : /* if no root page initialized yet, fail */
383 0 : if (metad->btm_root == P_NONE)
384 : {
385 0 : _bt_relbuf(rel, metabuf);
386 0 : return InvalidBuffer;
387 : }
388 :
389 0 : rootblkno = metad->btm_root;
390 0 : rootlevel = metad->btm_level;
391 :
392 : /*
393 : * We are done with the metapage; arrange to release it via first
394 : * _bt_relandgetbuf call
395 : */
396 0 : rootbuf = metabuf;
397 :
398 : for (;;)
399 : {
400 0 : rootbuf = _bt_relandgetbuf(rel, rootbuf, rootblkno, BT_READ);
401 0 : rootpage = BufferGetPage(rootbuf);
402 0 : rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
403 :
404 0 : if (!P_IGNORE(rootopaque))
405 0 : break;
406 :
407 : /* it's dead, Jim. step right one page */
408 0 : if (P_RIGHTMOST(rootopaque))
409 0 : elog(ERROR, "no live root page found in index \"%s\"",
410 : RelationGetRelationName(rel));
411 0 : rootblkno = rootopaque->btpo_next;
412 0 : }
413 :
414 : /* Note: can't check btpo.level on deleted pages */
415 0 : if (rootopaque->btpo.level != rootlevel)
416 0 : elog(ERROR, "root page %u of index \"%s\" has level %u, expected %u",
417 : rootblkno, RelationGetRelationName(rel),
418 : rootopaque->btpo.level, rootlevel);
419 :
420 0 : return rootbuf;
421 : }
422 :
423 : /*
424 : * _bt_getrootheight() -- Get the height of the btree search tree.
425 : *
426 : * We return the level (counting from zero) of the current fast root.
427 : * This represents the number of tree levels we'd have to descend through
428 : * to start any btree index search.
429 : *
430 : * This is used by the planner for cost-estimation purposes. Since it's
431 : * only an estimate, slightly-stale data is fine, hence we don't worry
432 : * about updating previously cached data.
433 : */
434 : int
435 21110 : _bt_getrootheight(Relation rel)
436 : {
437 : BTMetaPageData *metad;
438 :
439 : /*
440 : * We can get what we need from the cached metapage data. If it's not
441 : * cached yet, load it. Sanity checks here must match _bt_getroot().
442 : */
443 21110 : if (rel->rd_amcache == NULL)
444 : {
445 : Buffer metabuf;
446 : Page metapg;
447 : BTPageOpaque metaopaque;
448 :
449 1971 : metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
450 1971 : metapg = BufferGetPage(metabuf);
451 1971 : metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg);
452 1971 : metad = BTPageGetMeta(metapg);
453 :
454 : /* sanity-check the metapage */
455 3942 : if (!(metaopaque->btpo_flags & BTP_META) ||
456 1971 : metad->btm_magic != BTREE_MAGIC)
457 0 : ereport(ERROR,
458 : (errcode(ERRCODE_INDEX_CORRUPTED),
459 : errmsg("index \"%s\" is not a btree",
460 : RelationGetRelationName(rel))));
461 :
462 1971 : if (metad->btm_version != BTREE_VERSION)
463 0 : ereport(ERROR,
464 : (errcode(ERRCODE_INDEX_CORRUPTED),
465 : errmsg("version mismatch in index \"%s\": file version %d, code version %d",
466 : RelationGetRelationName(rel),
467 : metad->btm_version, BTREE_VERSION)));
468 :
469 : /*
470 : * If there's no root page yet, _bt_getroot() doesn't expect a cache
471 : * to be made, so just stop here and report the index height is zero.
472 : * (XXX perhaps _bt_getroot() should be changed to allow this case.)
473 : */
474 1971 : if (metad->btm_root == P_NONE)
475 : {
476 1232 : _bt_relbuf(rel, metabuf);
477 1232 : return 0;
478 : }
479 :
480 : /*
481 : * Cache the metapage data for next time
482 : */
483 739 : rel->rd_amcache = MemoryContextAlloc(rel->rd_indexcxt,
484 : sizeof(BTMetaPageData));
485 739 : memcpy(rel->rd_amcache, metad, sizeof(BTMetaPageData));
486 :
487 739 : _bt_relbuf(rel, metabuf);
488 : }
489 :
490 19878 : metad = (BTMetaPageData *) rel->rd_amcache;
491 : /* We shouldn't have cached it if any of these fail */
492 19878 : Assert(metad->btm_magic == BTREE_MAGIC);
493 19878 : Assert(metad->btm_version == BTREE_VERSION);
494 19878 : Assert(metad->btm_fastroot != P_NONE);
495 :
496 19878 : return metad->btm_fastlevel;
497 : }
498 :
499 : /*
500 : * _bt_checkpage() -- Verify that a freshly-read page looks sane.
501 : */
502 : void
503 1099593 : _bt_checkpage(Relation rel, Buffer buf)
504 : {
505 1099593 : Page page = BufferGetPage(buf);
506 :
507 : /*
508 : * ReadBuffer verifies that every newly-read page passes
509 : * PageHeaderIsValid, which means it either contains a reasonably sane
510 : * page header or is all-zero. We have to defend against the all-zero
511 : * case, however.
512 : */
513 1099593 : if (PageIsNew(page))
514 0 : ereport(ERROR,
515 : (errcode(ERRCODE_INDEX_CORRUPTED),
516 : errmsg("index \"%s\" contains unexpected zero page at block %u",
517 : RelationGetRelationName(rel),
518 : BufferGetBlockNumber(buf)),
519 : errhint("Please REINDEX it.")));
520 :
521 : /*
522 : * Additionally check that the special area looks sane.
523 : */
524 1099593 : if (PageGetSpecialSize(page) != MAXALIGN(sizeof(BTPageOpaqueData)))
525 0 : ereport(ERROR,
526 : (errcode(ERRCODE_INDEX_CORRUPTED),
527 : errmsg("index \"%s\" contains corrupted page at block %u",
528 : RelationGetRelationName(rel),
529 : BufferGetBlockNumber(buf)),
530 : errhint("Please REINDEX it.")));
531 1099593 : }
532 :
533 : /*
534 : * Log the reuse of a page from the FSM.
535 : */
536 : static void
537 0 : _bt_log_reuse_page(Relation rel, BlockNumber blkno, TransactionId latestRemovedXid)
538 : {
539 : xl_btree_reuse_page xlrec_reuse;
540 :
541 : /*
542 : * Note that we don't register the buffer with the record, because this
543 : * operation doesn't modify the page. This record only exists to provide a
544 : * conflict point for Hot Standby.
545 : */
546 :
547 : /* XLOG stuff */
548 0 : xlrec_reuse.node = rel->rd_node;
549 0 : xlrec_reuse.block = blkno;
550 0 : xlrec_reuse.latestRemovedXid = latestRemovedXid;
551 :
552 0 : XLogBeginInsert();
553 0 : XLogRegisterData((char *) &xlrec_reuse, SizeOfBtreeReusePage);
554 :
555 0 : XLogInsert(RM_BTREE_ID, XLOG_BTREE_REUSE_PAGE);
556 0 : }
557 :
558 : /*
559 : * _bt_getbuf() -- Get a buffer by block number for read or write.
560 : *
561 : * blkno == P_NEW means to get an unallocated index page. The page
562 : * will be initialized before returning it.
563 : *
564 : * When this routine returns, the appropriate lock is set on the
565 : * requested buffer and its reference count has been incremented
566 : * (ie, the buffer is "locked and pinned"). Also, we apply
567 : * _bt_checkpage to sanity-check the page (except in P_NEW case).
568 : */
569 : Buffer
570 604413 : _bt_getbuf(Relation rel, BlockNumber blkno, int access)
571 : {
572 : Buffer buf;
573 :
574 604413 : if (blkno != P_NEW)
575 : {
576 : /* Read an existing block of the relation */
577 603195 : buf = ReadBuffer(rel, blkno);
578 603195 : LockBuffer(buf, access);
579 603195 : _bt_checkpage(rel, buf);
580 : }
581 : else
582 : {
583 : bool needLock;
584 : Page page;
585 :
586 1218 : Assert(access == BT_WRITE);
587 :
588 : /*
589 : * First see if the FSM knows of any free pages.
590 : *
591 : * We can't trust the FSM's report unreservedly; we have to check that
592 : * the page is still free. (For example, an already-free page could
593 : * have been re-used between the time the last VACUUM scanned it and
594 : * the time the VACUUM made its FSM updates.)
595 : *
596 : * In fact, it's worse than that: we can't even assume that it's safe
597 : * to take a lock on the reported page. If somebody else has a lock
598 : * on it, or even worse our own caller does, we could deadlock. (The
599 : * own-caller scenario is actually not improbable. Consider an index
600 : * on a serial or timestamp column. Nearly all splits will be at the
601 : * rightmost page, so it's entirely likely that _bt_split will call us
602 : * while holding a lock on the page most recently acquired from FSM. A
603 : * VACUUM running concurrently with the previous split could well have
604 : * placed that page back in FSM.)
605 : *
606 : * To get around that, we ask for only a conditional lock on the
607 : * reported page. If we fail, then someone else is using the page,
608 : * and we may reasonably assume it's not free. (If we happen to be
609 : * wrong, the worst consequence is the page will be lost to use till
610 : * the next VACUUM, which is no big problem.)
611 : */
612 : for (;;)
613 : {
614 1218 : blkno = GetFreeIndexPage(rel);
615 1218 : if (blkno == InvalidBlockNumber)
616 1218 : break;
617 0 : buf = ReadBuffer(rel, blkno);
618 0 : if (ConditionalLockBuffer(buf))
619 : {
620 0 : page = BufferGetPage(buf);
621 0 : if (_bt_page_recyclable(page))
622 : {
623 : /*
624 : * If we are generating WAL for Hot Standby then create a
625 : * WAL record that will allow us to conflict with queries
626 : * running on standby.
627 : */
628 0 : if (XLogStandbyInfoActive() && RelationNeedsWAL(rel))
629 : {
630 0 : BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);
631 :
632 0 : _bt_log_reuse_page(rel, blkno, opaque->btpo.xact);
633 : }
634 :
635 : /* Okay to use page. Re-initialize and return it */
636 0 : _bt_pageinit(page, BufferGetPageSize(buf));
637 0 : return buf;
638 : }
639 0 : elog(DEBUG2, "FSM returned nonrecyclable page");
640 0 : _bt_relbuf(rel, buf);
641 : }
642 : else
643 : {
644 0 : elog(DEBUG2, "FSM returned nonlockable page");
645 : /* couldn't get lock, so just drop pin */
646 0 : ReleaseBuffer(buf);
647 : }
648 0 : }
649 :
650 : /*
651 : * Extend the relation by one page.
652 : *
653 : * We have to use a lock to ensure no one else is extending the rel at
654 : * the same time, else we will both try to initialize the same new
655 : * page. We can skip locking for new or temp relations, however,
656 : * since no one else could be accessing them.
657 : */
658 1218 : needLock = !RELATION_IS_LOCAL(rel);
659 :
660 1218 : if (needLock)
661 1154 : LockRelationForExtension(rel, ExclusiveLock);
662 :
663 1218 : buf = ReadBuffer(rel, P_NEW);
664 :
665 : /* Acquire buffer lock on new page */
666 1218 : LockBuffer(buf, BT_WRITE);
667 :
668 : /*
669 : * Release the file-extension lock; it's now OK for someone else to
670 : * extend the relation some more. Note that we cannot release this
671 : * lock before we have buffer lock on the new page, or we risk a race
672 : * condition against btvacuumscan --- see comments therein.
673 : */
674 1218 : if (needLock)
675 1154 : UnlockRelationForExtension(rel, ExclusiveLock);
676 :
677 : /* Initialize the new page before returning it */
678 1218 : page = BufferGetPage(buf);
679 1218 : Assert(PageIsNew(page));
680 1218 : _bt_pageinit(page, BufferGetPageSize(buf));
681 : }
682 :
683 : /* ref count and lock type are correct */
684 604413 : return buf;
685 : }
686 :
687 : /*
688 : * _bt_relandgetbuf() -- release a locked buffer and get another one.
689 : *
690 : * This is equivalent to _bt_relbuf followed by _bt_getbuf, with the
691 : * exception that blkno may not be P_NEW. Also, if obuf is InvalidBuffer
692 : * then it reduces to just _bt_getbuf; allowing this case simplifies some
693 : * callers.
694 : *
695 : * The original motivation for using this was to avoid two entries to the
696 : * bufmgr when one would do. However, now it's mainly just a notational
697 : * convenience. The only case where it saves work over _bt_relbuf/_bt_getbuf
698 : * is when the target page is the same one already in the buffer.
699 : */
700 : Buffer
701 494575 : _bt_relandgetbuf(Relation rel, Buffer obuf, BlockNumber blkno, int access)
702 : {
703 : Buffer buf;
704 :
705 494575 : Assert(blkno != P_NEW);
706 494575 : if (BufferIsValid(obuf))
707 492740 : LockBuffer(obuf, BUFFER_LOCK_UNLOCK);
708 494575 : buf = ReleaseAndReadBuffer(obuf, rel, blkno);
709 494575 : LockBuffer(buf, access);
710 494575 : _bt_checkpage(rel, buf);
711 494575 : return buf;
712 : }
713 :
714 : /*
715 : * _bt_relbuf() -- release a locked buffer.
716 : *
717 : * Lock and pin (refcount) are both dropped.
718 : */
719 : void
720 226663 : _bt_relbuf(Relation rel, Buffer buf)
721 : {
722 226663 : UnlockReleaseBuffer(buf);
723 226663 : }
724 :
725 : /*
726 : * _bt_pageinit() -- Initialize a new page.
727 : *
728 : * On return, the page header is initialized; data space is empty;
729 : * special space is zeroed out.
730 : */
731 : void
732 5061 : _bt_pageinit(Page page, Size size)
733 : {
734 5061 : PageInit(page, size, sizeof(BTPageOpaqueData));
735 5061 : }
736 :
737 : /*
738 : * _bt_page_recyclable() -- Is an existing page recyclable?
739 : *
740 : * This exists to make sure _bt_getbuf and btvacuumscan have the same
741 : * policy about whether a page is safe to re-use.
742 : */
743 : bool
744 1679 : _bt_page_recyclable(Page page)
745 : {
746 : BTPageOpaque opaque;
747 :
748 : /*
749 : * It's possible to find an all-zeroes page in an index --- for example, a
750 : * backend might successfully extend the relation one page and then crash
751 : * before it is able to make a WAL entry for adding the page. If we find a
752 : * zeroed page then reclaim it.
753 : */
754 1679 : if (PageIsNew(page))
755 0 : return true;
756 :
757 : /*
758 : * Otherwise, recycle if deleted and too old to have any processes
759 : * interested in it.
760 : */
761 1679 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
762 1679 : if (P_ISDELETED(opaque) &&
763 0 : TransactionIdPrecedes(opaque->btpo.xact, RecentGlobalXmin))
764 0 : return true;
765 1679 : return false;
766 : }
767 :
768 : /*
769 : * Delete item(s) from a btree page during VACUUM.
770 : *
771 : * This must only be used for deleting leaf items. Deleting an item on a
772 : * non-leaf page has to be done as part of an atomic action that includes
773 : * deleting the page it points to.
774 : *
775 : * This routine assumes that the caller has pinned and locked the buffer.
776 : * Also, the given itemnos *must* appear in increasing order in the array.
777 : *
778 : * We record VACUUMs and b-tree deletes differently in WAL. InHotStandby
779 : * we need to be able to pin all of the blocks in the btree in physical
780 : * order when replaying the effects of a VACUUM, just as we do for the
781 : * original VACUUM itself. lastBlockVacuumed allows us to tell whether an
782 : * intermediate range of blocks has had no changes at all by VACUUM,
783 : * and so must be scanned anyway during replay. We always write a WAL record
784 : * for the last block in the index, whether or not it contained any items
785 : * to be removed. This allows us to scan right up to end of index to
786 : * ensure correct locking.
787 : */
788 : void
789 563 : _bt_delitems_vacuum(Relation rel, Buffer buf,
790 : OffsetNumber *itemnos, int nitems,
791 : BlockNumber lastBlockVacuumed)
792 : {
793 563 : Page page = BufferGetPage(buf);
794 : BTPageOpaque opaque;
795 :
796 : /* No ereport(ERROR) until changes are logged */
797 563 : START_CRIT_SECTION();
798 :
799 : /* Fix the page */
800 563 : if (nitems > 0)
801 419 : PageIndexMultiDelete(page, itemnos, nitems);
802 :
803 : /*
804 : * We can clear the vacuum cycle ID since this page has certainly been
805 : * processed by the current vacuum scan.
806 : */
807 563 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
808 563 : opaque->btpo_cycleid = 0;
809 :
810 : /*
811 : * Mark the page as not containing any LP_DEAD items. This is not
812 : * certainly true (there might be some that have recently been marked, but
813 : * weren't included in our target-item list), but it will almost always be
814 : * true and it doesn't seem worth an additional page scan to check it.
815 : * Remember that BTP_HAS_GARBAGE is only a hint anyway.
816 : */
817 563 : opaque->btpo_flags &= ~BTP_HAS_GARBAGE;
818 :
819 563 : MarkBufferDirty(buf);
820 :
821 : /* XLOG stuff */
822 563 : if (RelationNeedsWAL(rel))
823 : {
824 : XLogRecPtr recptr;
825 : xl_btree_vacuum xlrec_vacuum;
826 :
827 563 : xlrec_vacuum.lastBlockVacuumed = lastBlockVacuumed;
828 :
829 563 : XLogBeginInsert();
830 563 : XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
831 563 : XLogRegisterData((char *) &xlrec_vacuum, SizeOfBtreeVacuum);
832 :
833 : /*
834 : * The target-offsets array is not in the buffer, but pretend that it
835 : * is. When XLogInsert stores the whole buffer, the offsets array
836 : * need not be stored too.
837 : */
838 563 : if (nitems > 0)
839 419 : XLogRegisterBufData(0, (char *) itemnos, nitems * sizeof(OffsetNumber));
840 :
841 563 : recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_VACUUM);
842 :
843 563 : PageSetLSN(page, recptr);
844 : }
845 :
846 563 : END_CRIT_SECTION();
847 563 : }
848 :
849 : /*
850 : * Delete item(s) from a btree page during single-page cleanup.
851 : *
852 : * As above, must only be used on leaf pages.
853 : *
854 : * This routine assumes that the caller has pinned and locked the buffer.
855 : * Also, the given itemnos *must* appear in increasing order in the array.
856 : *
857 : * This is nearly the same as _bt_delitems_vacuum as far as what it does to
858 : * the page, but the WAL logging considerations are quite different. See
859 : * comments for _bt_delitems_vacuum.
860 : */
861 : void
862 262 : _bt_delitems_delete(Relation rel, Buffer buf,
863 : OffsetNumber *itemnos, int nitems,
864 : Relation heapRel)
865 : {
866 262 : Page page = BufferGetPage(buf);
867 : BTPageOpaque opaque;
868 :
869 : /* Shouldn't be called unless there's something to do */
870 262 : Assert(nitems > 0);
871 :
872 : /* No ereport(ERROR) until changes are logged */
873 262 : START_CRIT_SECTION();
874 :
875 : /* Fix the page */
876 262 : PageIndexMultiDelete(page, itemnos, nitems);
877 :
878 : /*
879 : * Unlike _bt_delitems_vacuum, we *must not* clear the vacuum cycle ID,
880 : * because this is not called by VACUUM.
881 : */
882 :
883 : /*
884 : * Mark the page as not containing any LP_DEAD items. This is not
885 : * certainly true (there might be some that have recently been marked, but
886 : * weren't included in our target-item list), but it will almost always be
887 : * true and it doesn't seem worth an additional page scan to check it.
888 : * Remember that BTP_HAS_GARBAGE is only a hint anyway.
889 : */
890 262 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
891 262 : opaque->btpo_flags &= ~BTP_HAS_GARBAGE;
892 :
893 262 : MarkBufferDirty(buf);
894 :
895 : /* XLOG stuff */
896 262 : if (RelationNeedsWAL(rel))
897 : {
898 : XLogRecPtr recptr;
899 : xl_btree_delete xlrec_delete;
900 :
901 262 : xlrec_delete.hnode = heapRel->rd_node;
902 262 : xlrec_delete.nitems = nitems;
903 :
904 262 : XLogBeginInsert();
905 262 : XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
906 262 : XLogRegisterData((char *) &xlrec_delete, SizeOfBtreeDelete);
907 :
908 : /*
909 : * We need the target-offsets array whether or not we store the whole
910 : * buffer, to allow us to find the latestRemovedXid on a standby
911 : * server.
912 : */
913 262 : XLogRegisterData((char *) itemnos, nitems * sizeof(OffsetNumber));
914 :
915 262 : recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DELETE);
916 :
917 262 : PageSetLSN(page, recptr);
918 : }
919 :
920 262 : END_CRIT_SECTION();
921 262 : }
922 :
923 : /*
924 : * Returns true, if the given block has the half-dead flag set.
925 : */
926 : static bool
927 43 : _bt_is_page_halfdead(Relation rel, BlockNumber blk)
928 : {
929 : Buffer buf;
930 : Page page;
931 : BTPageOpaque opaque;
932 : bool result;
933 :
934 43 : buf = _bt_getbuf(rel, blk, BT_READ);
935 43 : page = BufferGetPage(buf);
936 43 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
937 :
938 43 : result = P_ISHALFDEAD(opaque);
939 43 : _bt_relbuf(rel, buf);
940 :
941 43 : return result;
942 : }
943 :
944 : /*
945 : * Subroutine to find the parent of the branch we're deleting. This climbs
946 : * up the tree until it finds a page with more than one child, i.e. a page
947 : * that will not be totally emptied by the deletion. The chain of pages below
948 : * it, with one downlink each, will form the branch that we need to delete.
949 : *
950 : * If we cannot remove the downlink from the parent, because it's the
951 : * rightmost entry, returns false. On success, *topparent and *topoff are set
952 : * to the buffer holding the parent, and the offset of the downlink in it.
953 : * *topparent is write-locked, the caller is responsible for releasing it when
954 : * done. *target is set to the topmost page in the branch to-be-deleted, i.e.
955 : * the page whose downlink *topparent / *topoff point to, and *rightsib to its
956 : * right sibling.
957 : *
958 : * "child" is the leaf page we wish to delete, and "stack" is a search stack
959 : * leading to it (approximately). Note that we will update the stack
960 : * entry(s) to reflect current downlink positions --- this is harmless and
961 : * indeed saves later search effort in _bt_pagedel. The caller should
962 : * initialize *target and *rightsib to the leaf page and its right sibling.
963 : *
964 : * Note: it's OK to release page locks on any internal pages between the leaf
965 : * and *topparent, because a safe deletion can't become unsafe due to
966 : * concurrent activity. An internal page can only acquire an entry if the
967 : * child is split, but that cannot happen as long as we hold a lock on the
968 : * leaf.
969 : */
970 : static bool
971 43 : _bt_lock_branch_parent(Relation rel, BlockNumber child, BTStack stack,
972 : Buffer *topparent, OffsetNumber *topoff,
973 : BlockNumber *target, BlockNumber *rightsib)
974 : {
975 : BlockNumber parent;
976 : OffsetNumber poffset,
977 : maxoff;
978 : Buffer pbuf;
979 : Page page;
980 : BTPageOpaque opaque;
981 : BlockNumber leftsib;
982 :
983 : /*
984 : * Locate the downlink of "child" in the parent (updating the stack entry
985 : * if needed)
986 : */
987 43 : ItemPointerSet(&(stack->bts_btentry.t_tid), child, P_HIKEY);
988 43 : pbuf = _bt_getstackbuf(rel, stack, BT_WRITE);
989 43 : if (pbuf == InvalidBuffer)
990 0 : elog(ERROR, "failed to re-find parent key in index \"%s\" for deletion target page %u",
991 : RelationGetRelationName(rel), child);
992 43 : parent = stack->bts_blkno;
993 43 : poffset = stack->bts_offset;
994 :
995 43 : page = BufferGetPage(pbuf);
996 43 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
997 43 : maxoff = PageGetMaxOffsetNumber(page);
998 :
999 : /*
1000 : * If the target is the rightmost child of its parent, then we can't
1001 : * delete, unless it's also the only child.
1002 : */
1003 43 : if (poffset >= maxoff)
1004 : {
1005 : /* It's rightmost child... */
1006 1 : if (poffset == P_FIRSTDATAKEY(opaque))
1007 : {
1008 : /*
1009 : * It's only child, so safe if parent would itself be removable.
1010 : * We have to check the parent itself, and then recurse to test
1011 : * the conditions at the parent's parent.
1012 : */
1013 0 : if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) ||
1014 0 : P_INCOMPLETE_SPLIT(opaque))
1015 : {
1016 0 : _bt_relbuf(rel, pbuf);
1017 0 : return false;
1018 : }
1019 :
1020 0 : *target = parent;
1021 0 : *rightsib = opaque->btpo_next;
1022 0 : leftsib = opaque->btpo_prev;
1023 :
1024 0 : _bt_relbuf(rel, pbuf);
1025 :
1026 : /*
1027 : * Like in _bt_pagedel, check that the left sibling is not marked
1028 : * with INCOMPLETE_SPLIT flag. That would mean that there is no
1029 : * downlink to the page to be deleted, and the page deletion
1030 : * algorithm isn't prepared to handle that.
1031 : */
1032 0 : if (leftsib != P_NONE)
1033 : {
1034 : Buffer lbuf;
1035 : Page lpage;
1036 : BTPageOpaque lopaque;
1037 :
1038 0 : lbuf = _bt_getbuf(rel, leftsib, BT_READ);
1039 0 : lpage = BufferGetPage(lbuf);
1040 0 : lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage);
1041 :
1042 : /*
1043 : * If the left sibling was concurrently split, so that its
1044 : * next-pointer doesn't point to the current page anymore, the
1045 : * split that created the current page must be completed. (We
1046 : * don't allow splitting an incompletely split page again
1047 : * until the previous split has been completed)
1048 : */
1049 0 : if (lopaque->btpo_next == parent &&
1050 0 : P_INCOMPLETE_SPLIT(lopaque))
1051 : {
1052 0 : _bt_relbuf(rel, lbuf);
1053 0 : return false;
1054 : }
1055 0 : _bt_relbuf(rel, lbuf);
1056 : }
1057 :
1058 : /*
1059 : * Perform the same check on this internal level that
1060 : * _bt_mark_page_halfdead performed on the leaf level.
1061 : */
1062 0 : if (_bt_is_page_halfdead(rel, *rightsib))
1063 : {
1064 0 : elog(DEBUG1, "could not delete page %u because its right sibling %u is half-dead",
1065 : parent, *rightsib);
1066 0 : return false;
1067 : }
1068 :
1069 0 : return _bt_lock_branch_parent(rel, parent, stack->bts_parent,
1070 : topparent, topoff, target, rightsib);
1071 : }
1072 : else
1073 : {
1074 : /* Unsafe to delete */
1075 1 : _bt_relbuf(rel, pbuf);
1076 1 : return false;
1077 : }
1078 : }
1079 : else
1080 : {
1081 : /* Not rightmost child, so safe to delete */
1082 42 : *topparent = pbuf;
1083 42 : *topoff = poffset;
1084 42 : return true;
1085 : }
1086 : }
1087 :
1088 : /*
1089 : * _bt_pagedel() -- Delete a page from the b-tree, if legal to do so.
1090 : *
1091 : * This action unlinks the page from the b-tree structure, removing all
1092 : * pointers leading to it --- but not touching its own left and right links.
1093 : * The page cannot be physically reclaimed right away, since other processes
1094 : * may currently be trying to follow links leading to the page; they have to
1095 : * be allowed to use its right-link to recover. See nbtree/README.
1096 : *
1097 : * On entry, the target buffer must be pinned and locked (either read or write
1098 : * lock is OK). This lock and pin will be dropped before exiting.
1099 : *
1100 : * Returns the number of pages successfully deleted (zero if page cannot
1101 : * be deleted now; could be more than one if parent or sibling pages were
1102 : * deleted too).
1103 : *
1104 : * NOTE: this leaks memory. Rather than trying to clean up everything
1105 : * carefully, it's better to run it in a temp context that can be reset
1106 : * frequently.
1107 : */
1108 : int
1109 52 : _bt_pagedel(Relation rel, Buffer buf)
1110 : {
1111 52 : int ndeleted = 0;
1112 : BlockNumber rightsib;
1113 : bool rightsib_empty;
1114 : Page page;
1115 : BTPageOpaque opaque;
1116 :
1117 : /*
1118 : * "stack" is a search stack leading (approximately) to the target page.
1119 : * It is initially NULL, but when iterating, we keep it to avoid
1120 : * duplicated search effort.
1121 : *
1122 : * Also, when "stack" is not NULL, we have already checked that the
1123 : * current page is not the right half of an incomplete split, i.e. the
1124 : * left sibling does not have its INCOMPLETE_SPLIT flag set.
1125 : */
1126 52 : BTStack stack = NULL;
1127 :
1128 : for (;;)
1129 : {
1130 95 : page = BufferGetPage(buf);
1131 95 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1132 :
1133 : /*
1134 : * Internal pages are never deleted directly, only as part of deleting
1135 : * the whole branch all the way down to leaf level.
1136 : */
1137 95 : if (!P_ISLEAF(opaque))
1138 : {
1139 : /*
1140 : * Pre-9.4 page deletion only marked internal pages as half-dead,
1141 : * but now we only use that flag on leaf pages. The old algorithm
1142 : * was never supposed to leave half-dead pages in the tree, it was
1143 : * just a transient state, but it was nevertheless possible in
1144 : * error scenarios. We don't know how to deal with them here. They
1145 : * are harmless as far as searches are considered, but inserts
1146 : * into the deleted keyspace could add out-of-order downlinks in
1147 : * the upper levels. Log a notice, hopefully the admin will notice
1148 : * and reindex.
1149 : */
1150 0 : if (P_ISHALFDEAD(opaque))
1151 0 : ereport(LOG,
1152 : (errcode(ERRCODE_INDEX_CORRUPTED),
1153 : errmsg("index \"%s\" contains a half-dead internal page",
1154 : RelationGetRelationName(rel)),
1155 : errhint("This can be caused by an interrupted VACUUM in version 9.3 or older, before upgrade. Please REINDEX it.")));
1156 0 : _bt_relbuf(rel, buf);
1157 0 : return ndeleted;
1158 : }
1159 :
1160 : /*
1161 : * We can never delete rightmost pages nor root pages. While at it,
1162 : * check that page is not already deleted and is empty.
1163 : *
1164 : * To keep the algorithm simple, we also never delete an incompletely
1165 : * split page (they should be rare enough that this doesn't make any
1166 : * meaningful difference to disk usage):
1167 : *
1168 : * The INCOMPLETE_SPLIT flag on the page tells us if the page is the
1169 : * left half of an incomplete split, but ensuring that it's not the
1170 : * right half is more complicated. For that, we have to check that
1171 : * the left sibling doesn't have its INCOMPLETE_SPLIT flag set. On
1172 : * the first iteration, we temporarily release the lock on the current
1173 : * page, and check the left sibling and also construct a search stack
1174 : * to. On subsequent iterations, we know we stepped right from a page
1175 : * that passed these tests, so it's OK.
1176 : */
1177 181 : if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || P_ISDELETED(opaque) ||
1178 172 : P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page) ||
1179 86 : P_INCOMPLETE_SPLIT(opaque))
1180 : {
1181 : /* Should never fail to delete a half-dead page */
1182 9 : Assert(!P_ISHALFDEAD(opaque));
1183 :
1184 9 : _bt_relbuf(rel, buf);
1185 9 : return ndeleted;
1186 : }
1187 :
1188 : /*
1189 : * First, remove downlink pointing to the page (or a parent of the
1190 : * page, if we are going to delete a taller branch), and mark the page
1191 : * as half-dead.
1192 : */
1193 86 : if (!P_ISHALFDEAD(opaque))
1194 : {
1195 : /*
1196 : * We need an approximate pointer to the page's parent page. We
1197 : * use the standard search mechanism to search for the page's high
1198 : * key; this will give us a link to either the current parent or
1199 : * someplace to its left (if there are multiple equal high keys).
1200 : *
1201 : * Also check if this is the right-half of an incomplete split
1202 : * (see comment above).
1203 : */
1204 86 : if (!stack)
1205 : {
1206 : ScanKey itup_scankey;
1207 : ItemId itemid;
1208 : IndexTuple targetkey;
1209 : Buffer lbuf;
1210 : BlockNumber leftsib;
1211 :
1212 43 : itemid = PageGetItemId(page, P_HIKEY);
1213 43 : targetkey = CopyIndexTuple((IndexTuple) PageGetItem(page, itemid));
1214 :
1215 43 : leftsib = opaque->btpo_prev;
1216 :
1217 : /*
1218 : * To avoid deadlocks, we'd better drop the leaf page lock
1219 : * before going further.
1220 : */
1221 43 : LockBuffer(buf, BUFFER_LOCK_UNLOCK);
1222 :
1223 : /*
1224 : * Fetch the left sibling, to check that it's not marked with
1225 : * INCOMPLETE_SPLIT flag. That would mean that the page
1226 : * to-be-deleted doesn't have a downlink, and the page
1227 : * deletion algorithm isn't prepared to handle that.
1228 : */
1229 43 : if (!P_LEFTMOST(opaque))
1230 : {
1231 : BTPageOpaque lopaque;
1232 : Page lpage;
1233 :
1234 43 : lbuf = _bt_getbuf(rel, leftsib, BT_READ);
1235 43 : lpage = BufferGetPage(lbuf);
1236 43 : lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage);
1237 :
1238 : /*
1239 : * If the left sibling is split again by another backend,
1240 : * after we released the lock, we know that the first
1241 : * split must have finished, because we don't allow an
1242 : * incompletely-split page to be split again. So we don't
1243 : * need to walk right here.
1244 : */
1245 86 : if (lopaque->btpo_next == BufferGetBlockNumber(buf) &&
1246 43 : P_INCOMPLETE_SPLIT(lopaque))
1247 : {
1248 0 : ReleaseBuffer(buf);
1249 0 : _bt_relbuf(rel, lbuf);
1250 0 : return ndeleted;
1251 : }
1252 43 : _bt_relbuf(rel, lbuf);
1253 : }
1254 :
1255 : /* we need an insertion scan key for the search, so build one */
1256 43 : itup_scankey = _bt_mkscankey(rel, targetkey);
1257 : /* find the leftmost leaf page containing this key */
1258 43 : stack = _bt_search(rel, rel->rd_rel->relnatts, itup_scankey,
1259 : false, &lbuf, BT_READ, NULL);
1260 : /* don't need a pin on the page */
1261 43 : _bt_relbuf(rel, lbuf);
1262 :
1263 : /*
1264 : * Re-lock the leaf page, and start over, to re-check that the
1265 : * page can still be deleted.
1266 : */
1267 43 : LockBuffer(buf, BT_WRITE);
1268 43 : continue;
1269 : }
1270 :
1271 43 : if (!_bt_mark_page_halfdead(rel, buf, stack))
1272 : {
1273 1 : _bt_relbuf(rel, buf);
1274 1 : return ndeleted;
1275 : }
1276 : }
1277 :
1278 : /*
1279 : * Then unlink it from its siblings. Each call to
1280 : * _bt_unlink_halfdead_page unlinks the topmost page from the branch,
1281 : * making it shallower. Iterate until the leaf page is gone.
1282 : */
1283 42 : rightsib_empty = false;
1284 126 : while (P_ISHALFDEAD(opaque))
1285 : {
1286 42 : if (!_bt_unlink_halfdead_page(rel, buf, &rightsib_empty))
1287 : {
1288 : /* _bt_unlink_halfdead_page already released buffer */
1289 0 : return ndeleted;
1290 : }
1291 42 : ndeleted++;
1292 : }
1293 :
1294 42 : rightsib = opaque->btpo_next;
1295 :
1296 42 : _bt_relbuf(rel, buf);
1297 :
1298 : /*
1299 : * The page has now been deleted. If its right sibling is completely
1300 : * empty, it's possible that the reason we haven't deleted it earlier
1301 : * is that it was the rightmost child of the parent. Now that we
1302 : * removed the downlink for this page, the right sibling might now be
1303 : * the only child of the parent, and could be removed. It would be
1304 : * picked up by the next vacuum anyway, but might as well try to
1305 : * remove it now, so loop back to process the right sibling.
1306 : */
1307 42 : if (!rightsib_empty)
1308 42 : break;
1309 :
1310 0 : buf = _bt_getbuf(rel, rightsib, BT_WRITE);
1311 43 : }
1312 :
1313 42 : return ndeleted;
1314 : }
1315 :
1316 : /*
1317 : * First stage of page deletion. Remove the downlink to the top of the
1318 : * branch being deleted, and mark the leaf page as half-dead.
1319 : */
1320 : static bool
1321 43 : _bt_mark_page_halfdead(Relation rel, Buffer leafbuf, BTStack stack)
1322 : {
1323 : BlockNumber leafblkno;
1324 : BlockNumber leafrightsib;
1325 : BlockNumber target;
1326 : BlockNumber rightsib;
1327 : ItemId itemid;
1328 : Page page;
1329 : BTPageOpaque opaque;
1330 : Buffer topparent;
1331 : OffsetNumber topoff;
1332 : OffsetNumber nextoffset;
1333 : IndexTuple itup;
1334 : IndexTupleData trunctuple;
1335 :
1336 43 : page = BufferGetPage(leafbuf);
1337 43 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1338 :
1339 43 : Assert(!P_RIGHTMOST(opaque) && !P_ISROOT(opaque) && !P_ISDELETED(opaque) &&
1340 : !P_ISHALFDEAD(opaque) && P_ISLEAF(opaque) &&
1341 : P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page));
1342 :
1343 : /*
1344 : * Save info about the leaf page.
1345 : */
1346 43 : leafblkno = BufferGetBlockNumber(leafbuf);
1347 43 : leafrightsib = opaque->btpo_next;
1348 :
1349 : /*
1350 : * Before attempting to lock the parent page, check that the right sibling
1351 : * is not in half-dead state. A half-dead right sibling would have no
1352 : * downlink in the parent, which would be highly confusing later when we
1353 : * delete the downlink that follows the current page's downlink. (I
1354 : * believe the deletion would work correctly, but it would fail the
1355 : * cross-check we make that the following downlink points to the right
1356 : * sibling of the delete page.)
1357 : */
1358 43 : if (_bt_is_page_halfdead(rel, leafrightsib))
1359 : {
1360 0 : elog(DEBUG1, "could not delete page %u because its right sibling %u is half-dead",
1361 : leafblkno, leafrightsib);
1362 0 : return false;
1363 : }
1364 :
1365 : /*
1366 : * We cannot delete a page that is the rightmost child of its immediate
1367 : * parent, unless it is the only child --- in which case the parent has to
1368 : * be deleted too, and the same condition applies recursively to it. We
1369 : * have to check this condition all the way up before trying to delete,
1370 : * and lock the final parent of the to-be-deleted branch.
1371 : */
1372 43 : rightsib = leafrightsib;
1373 43 : target = leafblkno;
1374 43 : if (!_bt_lock_branch_parent(rel, leafblkno, stack,
1375 : &topparent, &topoff, &target, &rightsib))
1376 1 : return false;
1377 :
1378 : /*
1379 : * Check that the parent-page index items we're about to delete/overwrite
1380 : * contain what we expect. This can fail if the index has become corrupt
1381 : * for some reason. We want to throw any error before entering the
1382 : * critical section --- otherwise it'd be a PANIC.
1383 : *
1384 : * The test on the target item is just an Assert because
1385 : * _bt_lock_branch_parent should have guaranteed it has the expected
1386 : * contents. The test on the next-child downlink is known to sometimes
1387 : * fail in the field, though.
1388 : */
1389 42 : page = BufferGetPage(topparent);
1390 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1391 :
1392 : #ifdef USE_ASSERT_CHECKING
1393 42 : itemid = PageGetItemId(page, topoff);
1394 42 : itup = (IndexTuple) PageGetItem(page, itemid);
1395 42 : Assert(ItemPointerGetBlockNumber(&(itup->t_tid)) == target);
1396 : #endif
1397 :
1398 42 : nextoffset = OffsetNumberNext(topoff);
1399 42 : itemid = PageGetItemId(page, nextoffset);
1400 42 : itup = (IndexTuple) PageGetItem(page, itemid);
1401 42 : if (ItemPointerGetBlockNumber(&(itup->t_tid)) != rightsib)
1402 0 : elog(ERROR, "right sibling %u of block %u is not next child %u of block %u in index \"%s\"",
1403 : rightsib, target, ItemPointerGetBlockNumber(&(itup->t_tid)),
1404 : BufferGetBlockNumber(topparent), RelationGetRelationName(rel));
1405 :
1406 : /*
1407 : * Any insert which would have gone on the leaf block will now go to its
1408 : * right sibling.
1409 : */
1410 42 : PredicateLockPageCombine(rel, leafblkno, leafrightsib);
1411 :
1412 : /* No ereport(ERROR) until changes are logged */
1413 42 : START_CRIT_SECTION();
1414 :
1415 : /*
1416 : * Update parent. The normal case is a tad tricky because we want to
1417 : * delete the target's downlink and the *following* key. Easiest way is
1418 : * to copy the right sibling's downlink over the target downlink, and then
1419 : * delete the following item.
1420 : */
1421 42 : page = BufferGetPage(topparent);
1422 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1423 :
1424 42 : itemid = PageGetItemId(page, topoff);
1425 42 : itup = (IndexTuple) PageGetItem(page, itemid);
1426 42 : ItemPointerSet(&(itup->t_tid), rightsib, P_HIKEY);
1427 :
1428 42 : nextoffset = OffsetNumberNext(topoff);
1429 42 : PageIndexTupleDelete(page, nextoffset);
1430 :
1431 : /*
1432 : * Mark the leaf page as half-dead, and stamp it with a pointer to the
1433 : * highest internal page in the branch we're deleting. We use the tid of
1434 : * the high key to store it.
1435 : */
1436 42 : page = BufferGetPage(leafbuf);
1437 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1438 42 : opaque->btpo_flags |= BTP_HALF_DEAD;
1439 :
1440 42 : PageIndexTupleDelete(page, P_HIKEY);
1441 42 : Assert(PageGetMaxOffsetNumber(page) == 0);
1442 42 : MemSet(&trunctuple, 0, sizeof(IndexTupleData));
1443 42 : trunctuple.t_info = sizeof(IndexTupleData);
1444 42 : if (target != leafblkno)
1445 0 : ItemPointerSet(&trunctuple.t_tid, target, P_HIKEY);
1446 : else
1447 42 : ItemPointerSetInvalid(&trunctuple.t_tid);
1448 42 : if (PageAddItem(page, (Item) &trunctuple, sizeof(IndexTupleData), P_HIKEY,
1449 : false, false) == InvalidOffsetNumber)
1450 0 : elog(ERROR, "could not add dummy high key to half-dead page");
1451 :
1452 : /* Must mark buffers dirty before XLogInsert */
1453 42 : MarkBufferDirty(topparent);
1454 42 : MarkBufferDirty(leafbuf);
1455 :
1456 : /* XLOG stuff */
1457 42 : if (RelationNeedsWAL(rel))
1458 : {
1459 : xl_btree_mark_page_halfdead xlrec;
1460 : XLogRecPtr recptr;
1461 :
1462 42 : xlrec.poffset = topoff;
1463 42 : xlrec.leafblk = leafblkno;
1464 42 : if (target != leafblkno)
1465 0 : xlrec.topparent = target;
1466 : else
1467 42 : xlrec.topparent = InvalidBlockNumber;
1468 :
1469 42 : XLogBeginInsert();
1470 42 : XLogRegisterBuffer(0, leafbuf, REGBUF_WILL_INIT);
1471 42 : XLogRegisterBuffer(1, topparent, REGBUF_STANDARD);
1472 :
1473 42 : page = BufferGetPage(leafbuf);
1474 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1475 42 : xlrec.leftblk = opaque->btpo_prev;
1476 42 : xlrec.rightblk = opaque->btpo_next;
1477 :
1478 42 : XLogRegisterData((char *) &xlrec, SizeOfBtreeMarkPageHalfDead);
1479 :
1480 42 : recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_MARK_PAGE_HALFDEAD);
1481 :
1482 42 : page = BufferGetPage(topparent);
1483 42 : PageSetLSN(page, recptr);
1484 42 : page = BufferGetPage(leafbuf);
1485 42 : PageSetLSN(page, recptr);
1486 : }
1487 :
1488 42 : END_CRIT_SECTION();
1489 :
1490 42 : _bt_relbuf(rel, topparent);
1491 42 : return true;
1492 : }
1493 :
1494 : /*
1495 : * Unlink a page in a branch of half-dead pages from its siblings.
1496 : *
1497 : * If the leaf page still has a downlink pointing to it, unlinks the highest
1498 : * parent in the to-be-deleted branch instead of the leaf page. To get rid
1499 : * of the whole branch, including the leaf page itself, iterate until the
1500 : * leaf page is deleted.
1501 : *
1502 : * Returns 'false' if the page could not be unlinked (shouldn't happen).
1503 : * If the (new) right sibling of the page is empty, *rightsib_empty is set
1504 : * to true.
1505 : *
1506 : * Must hold pin and lock on leafbuf at entry (read or write doesn't matter).
1507 : * On success exit, we'll be holding pin and write lock. On failure exit,
1508 : * we'll release both pin and lock before returning (we define it that way
1509 : * to avoid having to reacquire a lock we already released).
1510 : */
1511 : static bool
1512 42 : _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
1513 : {
1514 42 : BlockNumber leafblkno = BufferGetBlockNumber(leafbuf);
1515 : BlockNumber leafleftsib;
1516 : BlockNumber leafrightsib;
1517 : BlockNumber target;
1518 : BlockNumber leftsib;
1519 : BlockNumber rightsib;
1520 42 : Buffer lbuf = InvalidBuffer;
1521 : Buffer buf;
1522 : Buffer rbuf;
1523 42 : Buffer metabuf = InvalidBuffer;
1524 42 : Page metapg = NULL;
1525 42 : BTMetaPageData *metad = NULL;
1526 : ItemId itemid;
1527 : Page page;
1528 : BTPageOpaque opaque;
1529 : bool rightsib_is_rightmost;
1530 : int targetlevel;
1531 : ItemPointer leafhikey;
1532 : BlockNumber nextchild;
1533 :
1534 42 : page = BufferGetPage(leafbuf);
1535 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1536 :
1537 42 : Assert(P_ISLEAF(opaque) && P_ISHALFDEAD(opaque));
1538 :
1539 : /*
1540 : * Remember some information about the leaf page.
1541 : */
1542 42 : itemid = PageGetItemId(page, P_HIKEY);
1543 42 : leafhikey = &((IndexTuple) PageGetItem(page, itemid))->t_tid;
1544 42 : leafleftsib = opaque->btpo_prev;
1545 42 : leafrightsib = opaque->btpo_next;
1546 :
1547 42 : LockBuffer(leafbuf, BUFFER_LOCK_UNLOCK);
1548 :
1549 : /*
1550 : * If the leaf page still has a parent pointing to it (or a chain of
1551 : * parents), we don't unlink the leaf page yet, but the topmost remaining
1552 : * parent in the branch. Set 'target' and 'buf' to reference the page
1553 : * actually being unlinked.
1554 : */
1555 42 : if (ItemPointerIsValid(leafhikey))
1556 : {
1557 0 : target = ItemPointerGetBlockNumber(leafhikey);
1558 0 : Assert(target != leafblkno);
1559 :
1560 : /* fetch the block number of the topmost parent's left sibling */
1561 0 : buf = _bt_getbuf(rel, target, BT_READ);
1562 0 : page = BufferGetPage(buf);
1563 0 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1564 0 : leftsib = opaque->btpo_prev;
1565 0 : targetlevel = opaque->btpo.level;
1566 :
1567 : /*
1568 : * To avoid deadlocks, we'd better drop the target page lock before
1569 : * going further.
1570 : */
1571 0 : LockBuffer(buf, BUFFER_LOCK_UNLOCK);
1572 : }
1573 : else
1574 : {
1575 42 : target = leafblkno;
1576 :
1577 42 : buf = leafbuf;
1578 42 : leftsib = leafleftsib;
1579 42 : targetlevel = 0;
1580 : }
1581 :
1582 : /*
1583 : * We have to lock the pages we need to modify in the standard order:
1584 : * moving right, then up. Else we will deadlock against other writers.
1585 : *
1586 : * So, first lock the leaf page, if it's not the target. Then find and
1587 : * write-lock the current left sibling of the target page. The sibling
1588 : * that was current a moment ago could have split, so we may have to move
1589 : * right. This search could fail if either the sibling or the target page
1590 : * was deleted by someone else meanwhile; if so, give up. (Right now,
1591 : * that should never happen, since page deletion is only done in VACUUM
1592 : * and there shouldn't be multiple VACUUMs concurrently on the same
1593 : * table.)
1594 : */
1595 42 : if (target != leafblkno)
1596 0 : LockBuffer(leafbuf, BT_WRITE);
1597 42 : if (leftsib != P_NONE)
1598 : {
1599 42 : lbuf = _bt_getbuf(rel, leftsib, BT_WRITE);
1600 42 : page = BufferGetPage(lbuf);
1601 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1602 84 : while (P_ISDELETED(opaque) || opaque->btpo_next != target)
1603 : {
1604 : /* step right one page */
1605 0 : leftsib = opaque->btpo_next;
1606 0 : _bt_relbuf(rel, lbuf);
1607 0 : if (leftsib == P_NONE)
1608 : {
1609 0 : elog(LOG, "no left sibling (concurrent deletion?) of block %u in \"%s\"",
1610 : target,
1611 : RelationGetRelationName(rel));
1612 0 : if (target != leafblkno)
1613 : {
1614 : /* we have only a pin on target, but pin+lock on leafbuf */
1615 0 : ReleaseBuffer(buf);
1616 0 : _bt_relbuf(rel, leafbuf);
1617 : }
1618 : else
1619 : {
1620 : /* we have only a pin on leafbuf */
1621 0 : ReleaseBuffer(leafbuf);
1622 : }
1623 0 : return false;
1624 : }
1625 0 : lbuf = _bt_getbuf(rel, leftsib, BT_WRITE);
1626 0 : page = BufferGetPage(lbuf);
1627 0 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1628 : }
1629 : }
1630 : else
1631 0 : lbuf = InvalidBuffer;
1632 :
1633 : /*
1634 : * Next write-lock the target page itself. It should be okay to take just
1635 : * a write lock not a superexclusive lock, since no scans would stop on an
1636 : * empty page.
1637 : */
1638 42 : LockBuffer(buf, BT_WRITE);
1639 42 : page = BufferGetPage(buf);
1640 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1641 :
1642 : /*
1643 : * Check page is still empty etc, else abandon deletion. This is just for
1644 : * paranoia's sake; a half-dead page cannot resurrect because there can be
1645 : * only one vacuum process running at a time.
1646 : */
1647 42 : if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || P_ISDELETED(opaque))
1648 : {
1649 0 : elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"",
1650 : target, RelationGetRelationName(rel));
1651 : }
1652 42 : if (opaque->btpo_prev != leftsib)
1653 0 : elog(ERROR, "left link changed unexpectedly in block %u of index \"%s\"",
1654 : target, RelationGetRelationName(rel));
1655 :
1656 42 : if (target == leafblkno)
1657 : {
1658 84 : if (P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page) ||
1659 84 : !P_ISLEAF(opaque) || !P_ISHALFDEAD(opaque))
1660 0 : elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"",
1661 : target, RelationGetRelationName(rel));
1662 42 : nextchild = InvalidBlockNumber;
1663 : }
1664 : else
1665 : {
1666 0 : if (P_FIRSTDATAKEY(opaque) != PageGetMaxOffsetNumber(page) ||
1667 0 : P_ISLEAF(opaque))
1668 0 : elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"",
1669 : target, RelationGetRelationName(rel));
1670 :
1671 : /* remember the next non-leaf child down in the branch. */
1672 0 : itemid = PageGetItemId(page, P_FIRSTDATAKEY(opaque));
1673 0 : nextchild = ItemPointerGetBlockNumber(&((IndexTuple) PageGetItem(page, itemid))->t_tid);
1674 0 : if (nextchild == leafblkno)
1675 0 : nextchild = InvalidBlockNumber;
1676 : }
1677 :
1678 : /*
1679 : * And next write-lock the (current) right sibling.
1680 : */
1681 42 : rightsib = opaque->btpo_next;
1682 42 : rbuf = _bt_getbuf(rel, rightsib, BT_WRITE);
1683 42 : page = BufferGetPage(rbuf);
1684 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1685 42 : if (opaque->btpo_prev != target)
1686 0 : elog(ERROR, "right sibling's left-link doesn't match: "
1687 : "block %u links to %u instead of expected %u in index \"%s\"",
1688 : rightsib, opaque->btpo_prev, target,
1689 : RelationGetRelationName(rel));
1690 42 : rightsib_is_rightmost = P_RIGHTMOST(opaque);
1691 42 : *rightsib_empty = (P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page));
1692 :
1693 : /*
1694 : * If we are deleting the next-to-last page on the target's level, then
1695 : * the rightsib is a candidate to become the new fast root. (In theory, it
1696 : * might be possible to push the fast root even further down, but the odds
1697 : * of doing so are slim, and the locking considerations daunting.)
1698 : *
1699 : * We don't support handling this in the case where the parent is becoming
1700 : * half-dead, even though it theoretically could occur.
1701 : *
1702 : * We can safely acquire a lock on the metapage here --- see comments for
1703 : * _bt_newroot().
1704 : */
1705 42 : if (leftsib == P_NONE && rightsib_is_rightmost)
1706 : {
1707 0 : page = BufferGetPage(rbuf);
1708 0 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1709 0 : if (P_RIGHTMOST(opaque))
1710 : {
1711 : /* rightsib will be the only one left on the level */
1712 0 : metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_WRITE);
1713 0 : metapg = BufferGetPage(metabuf);
1714 0 : metad = BTPageGetMeta(metapg);
1715 :
1716 : /*
1717 : * The expected case here is btm_fastlevel == targetlevel+1; if
1718 : * the fastlevel is <= targetlevel, something is wrong, and we
1719 : * choose to overwrite it to fix it.
1720 : */
1721 0 : if (metad->btm_fastlevel > targetlevel + 1)
1722 : {
1723 : /* no update wanted */
1724 0 : _bt_relbuf(rel, metabuf);
1725 0 : metabuf = InvalidBuffer;
1726 : }
1727 : }
1728 : }
1729 :
1730 : /*
1731 : * Here we begin doing the deletion.
1732 : */
1733 :
1734 : /* No ereport(ERROR) until changes are logged */
1735 42 : START_CRIT_SECTION();
1736 :
1737 : /*
1738 : * Update siblings' side-links. Note the target page's side-links will
1739 : * continue to point to the siblings. Asserts here are just rechecking
1740 : * things we already verified above.
1741 : */
1742 42 : if (BufferIsValid(lbuf))
1743 : {
1744 42 : page = BufferGetPage(lbuf);
1745 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1746 42 : Assert(opaque->btpo_next == target);
1747 42 : opaque->btpo_next = rightsib;
1748 : }
1749 42 : page = BufferGetPage(rbuf);
1750 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1751 42 : Assert(opaque->btpo_prev == target);
1752 42 : opaque->btpo_prev = leftsib;
1753 :
1754 : /*
1755 : * If we deleted a parent of the targeted leaf page, instead of the leaf
1756 : * itself, update the leaf to point to the next remaining child in the
1757 : * branch.
1758 : */
1759 42 : if (target != leafblkno)
1760 : {
1761 0 : if (nextchild == InvalidBlockNumber)
1762 0 : ItemPointerSetInvalid(leafhikey);
1763 : else
1764 0 : ItemPointerSet(leafhikey, nextchild, P_HIKEY);
1765 : }
1766 :
1767 : /*
1768 : * Mark the page itself deleted. It can be recycled when all current
1769 : * transactions are gone. Storing GetTopTransactionId() would work, but
1770 : * we're in VACUUM and would not otherwise have an XID. Having already
1771 : * updated links to the target, ReadNewTransactionId() suffices as an
1772 : * upper bound. Any scan having retained a now-stale link is advertising
1773 : * in its PGXACT an xmin less than or equal to the value we read here. It
1774 : * will continue to do so, holding back RecentGlobalXmin, for the duration
1775 : * of that scan.
1776 : */
1777 42 : page = BufferGetPage(buf);
1778 42 : opaque = (BTPageOpaque) PageGetSpecialPointer(page);
1779 42 : opaque->btpo_flags &= ~BTP_HALF_DEAD;
1780 42 : opaque->btpo_flags |= BTP_DELETED;
1781 42 : opaque->btpo.xact = ReadNewTransactionId();
1782 :
1783 : /* And update the metapage, if needed */
1784 42 : if (BufferIsValid(metabuf))
1785 : {
1786 0 : metad->btm_fastroot = rightsib;
1787 0 : metad->btm_fastlevel = targetlevel;
1788 0 : MarkBufferDirty(metabuf);
1789 : }
1790 :
1791 : /* Must mark buffers dirty before XLogInsert */
1792 42 : MarkBufferDirty(rbuf);
1793 42 : MarkBufferDirty(buf);
1794 42 : if (BufferIsValid(lbuf))
1795 42 : MarkBufferDirty(lbuf);
1796 42 : if (target != leafblkno)
1797 0 : MarkBufferDirty(leafbuf);
1798 :
1799 : /* XLOG stuff */
1800 42 : if (RelationNeedsWAL(rel))
1801 : {
1802 : xl_btree_unlink_page xlrec;
1803 : xl_btree_metadata xlmeta;
1804 : uint8 xlinfo;
1805 : XLogRecPtr recptr;
1806 :
1807 42 : XLogBeginInsert();
1808 :
1809 42 : XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
1810 42 : if (BufferIsValid(lbuf))
1811 42 : XLogRegisterBuffer(1, lbuf, REGBUF_STANDARD);
1812 42 : XLogRegisterBuffer(2, rbuf, REGBUF_STANDARD);
1813 42 : if (target != leafblkno)
1814 0 : XLogRegisterBuffer(3, leafbuf, REGBUF_WILL_INIT);
1815 :
1816 : /* information on the unlinked block */
1817 42 : xlrec.leftsib = leftsib;
1818 42 : xlrec.rightsib = rightsib;
1819 42 : xlrec.btpo_xact = opaque->btpo.xact;
1820 :
1821 : /* information needed to recreate the leaf block (if not the target) */
1822 42 : xlrec.leafleftsib = leafleftsib;
1823 42 : xlrec.leafrightsib = leafrightsib;
1824 42 : xlrec.topparent = nextchild;
1825 :
1826 42 : XLogRegisterData((char *) &xlrec, SizeOfBtreeUnlinkPage);
1827 :
1828 42 : if (BufferIsValid(metabuf))
1829 : {
1830 0 : XLogRegisterBuffer(4, metabuf, REGBUF_WILL_INIT);
1831 :
1832 0 : xlmeta.root = metad->btm_root;
1833 0 : xlmeta.level = metad->btm_level;
1834 0 : xlmeta.fastroot = metad->btm_fastroot;
1835 0 : xlmeta.fastlevel = metad->btm_fastlevel;
1836 :
1837 0 : XLogRegisterBufData(4, (char *) &xlmeta, sizeof(xl_btree_metadata));
1838 0 : xlinfo = XLOG_BTREE_UNLINK_PAGE_META;
1839 : }
1840 : else
1841 42 : xlinfo = XLOG_BTREE_UNLINK_PAGE;
1842 :
1843 42 : recptr = XLogInsert(RM_BTREE_ID, xlinfo);
1844 :
1845 42 : if (BufferIsValid(metabuf))
1846 : {
1847 0 : PageSetLSN(metapg, recptr);
1848 : }
1849 42 : page = BufferGetPage(rbuf);
1850 42 : PageSetLSN(page, recptr);
1851 42 : page = BufferGetPage(buf);
1852 42 : PageSetLSN(page, recptr);
1853 42 : if (BufferIsValid(lbuf))
1854 : {
1855 42 : page = BufferGetPage(lbuf);
1856 42 : PageSetLSN(page, recptr);
1857 : }
1858 42 : if (target != leafblkno)
1859 : {
1860 0 : page = BufferGetPage(leafbuf);
1861 0 : PageSetLSN(page, recptr);
1862 : }
1863 : }
1864 :
1865 42 : END_CRIT_SECTION();
1866 :
1867 : /* release metapage */
1868 42 : if (BufferIsValid(metabuf))
1869 0 : _bt_relbuf(rel, metabuf);
1870 :
1871 : /* release siblings */
1872 42 : if (BufferIsValid(lbuf))
1873 42 : _bt_relbuf(rel, lbuf);
1874 42 : _bt_relbuf(rel, rbuf);
1875 :
1876 : /*
1877 : * Release the target, if it was not the leaf block. The leaf is always
1878 : * kept locked.
1879 : */
1880 42 : if (target != leafblkno)
1881 0 : _bt_relbuf(rel, buf);
1882 :
1883 42 : return true;
1884 : }
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