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Commit73a076b

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Fix undercounting in VACUUM VERBOSE output.
The logic for determining how many nbtree pages in an index are deletedpages sometimes undercounted pages. Pages that were deleted by thecurrent VACUUM operation (as opposed to some previous VACUUM operationwhose deleted pages have yet to be reused) were sometimes overlooked.The final count is exposed to users through VACUUM VERBOSE's "%u indexpages have been deleted" output.btvacuumpage() avoided double-counting when _bt_pagedel() deleted morethan one page by assuming that only one page was deleted, and that theadditional deleted pages would get picked up during a future call tobtvacuumpage() by the same VACUUM operation. _bt_pagedel() canlegitimately delete pages that the btvacuumscan() scan will not visitagain, though, so that assumption was slightly faulty.Fix the accounting by teaching _bt_pagedel() about its caller'srequirements. It now only reports on pages that it knows btvacuumscan()won't visit again (including the current btvacuumpage() page), soeverything works out in the end.This bug has been around forever. Only backpatch to v11, though, tokeep _bt_pagedel() is sync on the branches that have today's bugfixcommitb0229f2. Note that this commit changes the signature of_bt_pagedel(), just like commitb0229f2.Author: Peter GeogheganReviewed-By: Masahiko SawadaDiscussion:https://postgr.es/m/CAH2-WzkrXBcMQWAYUJMFTTvzx_r4q=pYSjDe07JnUXhe+OZnJA@mail.gmail.comBackpatch: 11-
1 parentb0229f2 commit73a076b

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3 files changed

+38
-18
lines changed

3 files changed

+38
-18
lines changed

‎src/backend/access/nbtree/nbtpage.c

Lines changed: 30 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -38,8 +38,10 @@ static BTMetaPageData *_bt_getmeta(Relation rel, Buffer metabuf);
3838
staticbool_bt_mark_page_halfdead(Relationrel,Bufferleafbuf,
3939
BTStackstack);
4040
staticbool_bt_unlink_halfdead_page(Relationrel,Bufferleafbuf,
41+
BlockNumberscanblkno,
4142
bool*rightsib_empty,
42-
TransactionId*oldestBtpoXact);
43+
TransactionId*oldestBtpoXact,
44+
uint32*ndeleted);
4345
staticTransactionId_bt_xid_horizon(Relationrel,RelationheapRel,Pagepage,
4446
OffsetNumber*deletable,intndeletable);
4547
staticbool_bt_lock_branch_parent(Relationrel,BlockNumberchild,
@@ -1489,7 +1491,9 @@ _bt_lock_branch_parent(Relation rel, BlockNumber child, BTStack stack,
14891491
*
14901492
* Returns the number of pages successfully deleted (zero if page cannot
14911493
* be deleted now; could be more than one if parent or right sibling pages
1492-
* were deleted too).
1494+
* were deleted too). Note that this does not include pages that we delete
1495+
* that the btvacuumscan scan has yet to reach; they'll get counted later
1496+
* instead.
14931497
*
14941498
* Maintains *oldestBtpoXact for any pages that get deleted. Caller is
14951499
* responsible for maintaining *oldestBtpoXact in the case of pages that were
@@ -1499,15 +1503,21 @@ _bt_lock_branch_parent(Relation rel, BlockNumber child, BTStack stack,
14991503
* carefully, it's better to run it in a temp context that can be reset
15001504
* frequently.
15011505
*/
1502-
int
1506+
uint32
15031507
_bt_pagedel(Relationrel,Bufferleafbuf,TransactionId*oldestBtpoXact)
15041508
{
1505-
intndeleted=0;
1509+
uint32ndeleted=0;
15061510
BlockNumberrightsib;
15071511
boolrightsib_empty;
15081512
Pagepage;
15091513
BTPageOpaqueopaque;
15101514

1515+
/*
1516+
* Save original leafbuf block number from caller. Only deleted blocks
1517+
* that are <= scanblkno get counted in ndeleted return value.
1518+
*/
1519+
BlockNumberscanblkno=BufferGetBlockNumber(leafbuf);
1520+
15111521
/*
15121522
* "stack" is a search stack leading (approximately) to the target page.
15131523
* It is initially NULL, but when iterating, we keep it to avoid
@@ -1558,8 +1568,9 @@ _bt_pagedel(Relation rel, Buffer leafbuf, TransactionId *oldestBtpoXact)
15581568
if (P_ISDELETED(opaque))
15591569
ereport(LOG,
15601570
(errcode(ERRCODE_INDEX_CORRUPTED),
1561-
errmsg_internal("found deleted block %u while following right link in index \"%s\"",
1571+
errmsg_internal("found deleted block %u while following right linkfrom block %uin index \"%s\"",
15621572
BufferGetBlockNumber(leafbuf),
1573+
scanblkno,
15631574
RelationGetRelationName(rel))));
15641575

15651576
_bt_relbuf(rel,leafbuf);
@@ -1709,13 +1720,13 @@ _bt_pagedel(Relation rel, Buffer leafbuf, TransactionId *oldestBtpoXact)
17091720
while (P_ISHALFDEAD(opaque))
17101721
{
17111722
/* Check for interrupts in _bt_unlink_halfdead_page */
1712-
if (!_bt_unlink_halfdead_page(rel,leafbuf,&rightsib_empty,
1713-
oldestBtpoXact))
1723+
if (!_bt_unlink_halfdead_page(rel,leafbuf,scanblkno,
1724+
&rightsib_empty,oldestBtpoXact,
1725+
&ndeleted))
17141726
{
17151727
/* _bt_unlink_halfdead_page failed, released buffer */
17161728
returnndeleted;
17171729
}
1718-
ndeleted++;
17191730
}
17201731

17211732
Assert(P_ISLEAF(opaque)&&P_ISDELETED(opaque));
@@ -1974,8 +1985,9 @@ _bt_mark_page_halfdead(Relation rel, Buffer leafbuf, BTStack stack)
19741985
* to avoid having to reacquire a lock we already released).
19751986
*/
19761987
staticbool
1977-
_bt_unlink_halfdead_page(Relationrel,Bufferleafbuf,bool*rightsib_empty,
1978-
TransactionId*oldestBtpoXact)
1988+
_bt_unlink_halfdead_page(Relationrel,Bufferleafbuf,BlockNumberscanblkno,
1989+
bool*rightsib_empty,TransactionId*oldestBtpoXact,
1990+
uint32*ndeleted)
19791991
{
19801992
BlockNumberleafblkno=BufferGetBlockNumber(leafbuf);
19811993
BlockNumberleafleftsib;
@@ -2370,6 +2382,14 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty,
23702382
TransactionIdPrecedes(opaque->btpo.xact,*oldestBtpoXact))
23712383
*oldestBtpoXact=opaque->btpo.xact;
23722384

2385+
/*
2386+
* If btvacuumscan won't revisit this page in a future btvacuumpage call
2387+
* and count it as deleted then, we count it as deleted by current
2388+
* btvacuumpage call
2389+
*/
2390+
if (target <=scanblkno)
2391+
(*ndeleted)++;
2392+
23732393
/*
23742394
* Release the target, if it was not the leaf block. The leaf is always
23752395
* kept locked.

‎src/backend/access/nbtree/nbtree.c

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1362,17 +1362,17 @@ btvacuumpage(BTVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
13621362
if (delete_now)
13631363
{
13641364
MemoryContextoldcontext;
1365-
intndel;
13661365

13671366
/* Run pagedel in a temp context to avoid memory leakage */
13681367
MemoryContextReset(vstate->pagedelcontext);
13691368
oldcontext=MemoryContextSwitchTo(vstate->pagedelcontext);
13701369

1371-
ndel=_bt_pagedel(rel,buf,&vstate->oldestBtpoXact);
1372-
1373-
/* count only this page, else may double-count parent */
1374-
if (ndel)
1375-
stats->pages_deleted++;
1370+
/*
1371+
* We trust the _bt_pagedel return value because it does not include
1372+
* any page that a future call here from btvacuumscan is expected to
1373+
* count. There will be no double-counting.
1374+
*/
1375+
stats->pages_deleted+=_bt_pagedel(rel,buf,&vstate->oldestBtpoXact);
13761376

13771377
MemoryContextSwitchTo(oldcontext);
13781378
/* pagedel released buffer, so we shouldn't */

‎src/include/access/nbtree.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1080,8 +1080,8 @@ extern void _bt_delitems_vacuum(Relation rel, Buffer buf,
10801080
externvoid_bt_delitems_delete(Relationrel,Bufferbuf,
10811081
OffsetNumber*deletable,intndeletable,
10821082
RelationheapRel);
1083-
externint_bt_pagedel(Relationrel,Bufferleafbuf,
1084-
TransactionId*oldestBtpoXact);
1083+
externuint32_bt_pagedel(Relationrel,Bufferleafbuf,
1084+
TransactionId*oldestBtpoXact);
10851085

10861086
/*
10871087
* prototypes for functions in nbtsearch.c

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