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Commitd3944c3

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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 parente4fa6c9 commitd3944c3

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3 files changed

+37
-18
lines changed

3 files changed

+37
-18
lines changed

‎src/backend/access/nbtree/nbtpage.c

Lines changed: 29 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -35,7 +35,8 @@
3535

3636
staticbool_bt_mark_page_halfdead(Relationrel,Bufferleafbuf,BTStackstack);
3737
staticbool_bt_unlink_halfdead_page(Relationrel,Bufferleafbuf,
38-
bool*rightsib_empty,TransactionId*oldestBtpoXact);
38+
BlockNumberscanblkno,bool*rightsib_empty,
39+
TransactionId*oldestBtpoXact,uint32*ndeleted);
3940
staticbool_bt_lock_branch_parent(Relationrel,BlockNumberchild,
4041
BTStackstack,Buffer*topparent,OffsetNumber*topoff,
4142
BlockNumber*target,BlockNumber*rightsib);
@@ -1236,7 +1237,9 @@ _bt_lock_branch_parent(Relation rel, BlockNumber child, BTStack stack,
12361237
*
12371238
* Returns the number of pages successfully deleted (zero if page cannot
12381239
* be deleted now; could be more than one if parent or right sibling pages
1239-
* were deleted too).
1240+
* were deleted too). Note that this does not include pages that we delete
1241+
* that the btvacuumscan scan has yet to reach; they'll get counted later
1242+
* instead.
12401243
*
12411244
* Maintains *oldestBtpoXact for any pages that get deleted. Caller is
12421245
* responsible for maintaining *oldestBtpoXact in the case of pages that were
@@ -1246,15 +1249,21 @@ _bt_lock_branch_parent(Relation rel, BlockNumber child, BTStack stack,
12461249
* carefully, it's better to run it in a temp context that can be reset
12471250
* frequently.
12481251
*/
1249-
int
1252+
uint32
12501253
_bt_pagedel(Relationrel,Bufferleafbuf,TransactionId*oldestBtpoXact)
12511254
{
1252-
intndeleted=0;
1255+
uint32ndeleted=0;
12531256
BlockNumberrightsib;
12541257
boolrightsib_empty;
12551258
Pagepage;
12561259
BTPageOpaqueopaque;
12571260

1261+
/*
1262+
* Save original leafbuf block number from caller. Only deleted blocks
1263+
* that are <= scanblkno get counted in ndeleted return value.
1264+
*/
1265+
BlockNumberscanblkno=BufferGetBlockNumber(leafbuf);
1266+
12581267
/*
12591268
* "stack" is a search stack leading (approximately) to the target page.
12601269
* It is initially NULL, but when iterating, we keep it to avoid
@@ -1305,8 +1314,9 @@ _bt_pagedel(Relation rel, Buffer leafbuf, TransactionId *oldestBtpoXact)
13051314
if (P_ISDELETED(opaque))
13061315
ereport(LOG,
13071316
(errcode(ERRCODE_INDEX_CORRUPTED),
1308-
errmsg_internal("found deleted block %u while following right link in index \"%s\"",
1317+
errmsg_internal("found deleted block %u while following right linkfrom block %uin index \"%s\"",
13091318
BufferGetBlockNumber(leafbuf),
1319+
scanblkno,
13101320
RelationGetRelationName(rel))));
13111321

13121322
_bt_relbuf(rel,leafbuf);
@@ -1456,13 +1466,13 @@ _bt_pagedel(Relation rel, Buffer leafbuf, TransactionId *oldestBtpoXact)
14561466
while (P_ISHALFDEAD(opaque))
14571467
{
14581468
/* Check for interrupts in _bt_unlink_halfdead_page */
1459-
if (!_bt_unlink_halfdead_page(rel,leafbuf,&rightsib_empty,
1460-
oldestBtpoXact))
1469+
if (!_bt_unlink_halfdead_page(rel,leafbuf,scanblkno,
1470+
&rightsib_empty,oldestBtpoXact,
1471+
&ndeleted))
14611472
{
14621473
/* _bt_unlink_halfdead_page failed, released buffer */
14631474
returnndeleted;
14641475
}
1465-
ndeleted++;
14661476
}
14671477

14681478
Assert(P_ISLEAF(opaque)&&P_ISDELETED(opaque));
@@ -1704,8 +1714,9 @@ _bt_mark_page_halfdead(Relation rel, Buffer leafbuf, BTStack stack)
17041714
* to avoid having to reacquire a lock we already released).
17051715
*/
17061716
staticbool
1707-
_bt_unlink_halfdead_page(Relationrel,Bufferleafbuf,bool*rightsib_empty,
1708-
TransactionId*oldestBtpoXact)
1717+
_bt_unlink_halfdead_page(Relationrel,Bufferleafbuf,BlockNumberscanblkno,
1718+
bool*rightsib_empty,TransactionId*oldestBtpoXact,
1719+
uint32*ndeleted)
17091720
{
17101721
BlockNumberleafblkno=BufferGetBlockNumber(leafbuf);
17111722
BlockNumberleafleftsib;
@@ -2089,6 +2100,14 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty,
20892100
TransactionIdPrecedes(opaque->btpo.xact,*oldestBtpoXact))
20902101
*oldestBtpoXact=opaque->btpo.xact;
20912102

2103+
/*
2104+
* If btvacuumscan won't revisit this page in a future btvacuumpage call
2105+
* and count it as deleted then, we count it as deleted by current
2106+
* btvacuumpage call
2107+
*/
2108+
if (target <=scanblkno)
2109+
(*ndeleted)++;
2110+
20922111
/*
20932112
* Release the target, if it was not the leaf block. The leaf is always
20942113
* kept locked.

‎src/backend/access/nbtree/nbtree.c

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1340,17 +1340,17 @@ btvacuumpage(BTVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
13401340
if (delete_now)
13411341
{
13421342
MemoryContextoldcontext;
1343-
intndel;
13441343

13451344
/* Run pagedel in a temp context to avoid memory leakage */
13461345
MemoryContextReset(vstate->pagedelcontext);
13471346
oldcontext=MemoryContextSwitchTo(vstate->pagedelcontext);
13481347

1349-
ndel=_bt_pagedel(rel,buf,&vstate->oldestBtpoXact);
1350-
1351-
/* count only this page, else may double-count parent */
1352-
if (ndel)
1353-
stats->pages_deleted++;
1348+
/*
1349+
* We trust the _bt_pagedel return value because it does not include
1350+
* any page that a future call here from btvacuumscan is expected to
1351+
* count. There will be no double-counting.
1352+
*/
1353+
stats->pages_deleted+=_bt_pagedel(rel,buf,&vstate->oldestBtpoXact);
13541354

13551355
MemoryContextSwitchTo(oldcontext);
13561356
/* 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
@@ -553,8 +553,8 @@ extern void _bt_delitems_delete(Relation rel, Buffer buf,
553553
externvoid_bt_delitems_vacuum(Relationrel,Bufferbuf,
554554
OffsetNumber*itemnos,intnitems,
555555
BlockNumberlastBlockVacuumed);
556-
externint_bt_pagedel(Relationrel,Bufferleafbuf,
557-
TransactionId*oldestBtpoXact);
556+
externuint32_bt_pagedel(Relationrel,Bufferleafbuf,
557+
TransactionId*oldestBtpoXact);
558558

559559
/*
560560
* prototypes for functions in nbtsearch.c

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