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Commit8c19977

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Avoid changing an index's indcheckxmin horizon during REINDEX.
There can never be a need to push the indcheckxmin horizon forward, sinceany HOT chains that are actually broken with respect to the index mustpre-date its original creation. So we can just avoid changing pg_indexaltogether during a REINDEX operation.This offers a cleaner solution than my previous patch for the problemfound a few days ago that we mustn't try to update pg_index while we arereindexing it. System catalog indexes will always be created withindcheckxmin = false during initdb, and with this modified code we shouldnever try to change their pg_index entries. This avoids special-casingsystem catalogs as the former patch did, and should provide a performancebenefit for many cases where REINDEX formerly caused an index to beconsidered unusable for a short time.Back-patch to 8.3 to cover all versions containing HOT. Note that thispatch changes the API for index_build(), but I believe it is unlikely thatany add-on code is calling that directly.
1 parentc096d19 commit8c19977

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6 files changed

+42
-11
lines changed

6 files changed

+42
-11
lines changed

‎src/backend/bootstrap/bootstrap.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1134,7 +1134,7 @@ build_indices(void)
11341134
heap=heap_open(ILHead->il_heap,NoLock);
11351135
ind=index_open(ILHead->il_ind,NoLock);
11361136

1137-
index_build(heap,ind,ILHead->il_info, false);
1137+
index_build(heap,ind,ILHead->il_info, false, false);
11381138

11391139
index_close(ind,NoLock);
11401140
heap_close(heap,NoLock);

‎src/backend/catalog/heap.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2569,7 +2569,7 @@ RelationTruncateIndexes(Relation heapRelation)
25692569

25702570
/* Initialize the index and rebuild */
25712571
/* Note: we do not need to re-establish pkey setting */
2572-
index_build(heapRelation,currentIndex,indexInfo, false);
2572+
index_build(heapRelation,currentIndex,indexInfo, false, true);
25732573

25742574
/* We're done with this index */
25752575
index_close(currentIndex,NoLock);

‎src/backend/catalog/index.c

Lines changed: 31 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1061,7 +1061,7 @@ index_create(Relation heapRelation,
10611061
}
10621062
else
10631063
{
1064-
index_build(heapRelation,indexRelation,indexInfo,isprimary);
1064+
index_build(heapRelation,indexRelation,indexInfo,isprimary, false);
10651065
}
10661066

10671067
/*
@@ -1680,8 +1680,11 @@ index_update_stats(Relation rel,
16801680
* entries of the index and heap relation as needed, using statistics
16811681
* returned by ambuild as well as data passed by the caller.
16821682
*
1683-
* Note: when reindexing an existing index, isprimary can be false;
1684-
* the index is already properly marked and need not be re-marked.
1683+
* isprimary tells whether to mark the index as a primary-key index.
1684+
* isreindex indicates we are recreating a previously-existing index.
1685+
*
1686+
* Note: when reindexing an existing index, isprimary can be false even if
1687+
* the index is a PK; it's already properly marked and need not be re-marked.
16851688
*
16861689
* Note: before Postgres 8.2, the passed-in heap and index Relations
16871690
* were automatically closed by this routine. This is no longer the case.
@@ -1691,7 +1694,8 @@ void
16911694
index_build(RelationheapRelation,
16921695
RelationindexRelation,
16931696
IndexInfo*indexInfo,
1694-
boolisprimary)
1697+
boolisprimary,
1698+
boolisreindex)
16951699
{
16961700
RegProcedureprocedure;
16971701
IndexBuildResult*stats;
@@ -1762,8 +1766,15 @@ index_build(Relation heapRelation,
17621766
* If we found any potentially broken HOT chains, mark the index as not
17631767
* being usable until the current transaction is below the event horizon.
17641768
* See src/backend/access/heap/README.HOT for discussion.
1765-
*/
1766-
if (indexInfo->ii_BrokenHotChain)
1769+
*
1770+
* However, when reindexing an existing index, we should do nothing here.
1771+
* Any HOT chains that are broken with respect to the index must predate
1772+
* the index's original creation, so there is no need to change the
1773+
* index's usability horizon. Moreover, we *must not* try to change
1774+
* the index's pg_index entry while reindexing pg_index itself, and this
1775+
* optimization nicely prevents that.
1776+
*/
1777+
if (indexInfo->ii_BrokenHotChain&& !isreindex)
17671778
{
17681779
OidindexId=RelationGetRelid(indexRelation);
17691780
Relationpg_index;
@@ -1778,6 +1789,9 @@ index_build(Relation heapRelation,
17781789
elog(ERROR,"cache lookup failed for index %u",indexId);
17791790
indexForm= (Form_pg_index)GETSTRUCT(indexTuple);
17801791

1792+
/* If it's a new index, indcheckxmin shouldn't be set ... */
1793+
Assert(!indexForm->indcheckxmin);
1794+
17811795
indexForm->indcheckxmin= true;
17821796
simple_heap_update(pg_index,&indexTuple->t_self,indexTuple);
17831797
CatalogUpdateIndexes(pg_index,indexTuple);
@@ -2767,7 +2781,7 @@ reindex_index(Oid indexId, bool skip_constraint_checks)
27672781

27682782
/* Initialize the index and rebuild */
27692783
/* Note: we do not need to re-establish pkey setting */
2770-
index_build(heapRelation,iRel,indexInfo, false);
2784+
index_build(heapRelation,iRel,indexInfo, false, true);
27712785
}
27722786
PG_CATCH();
27732787
{
@@ -2787,6 +2801,16 @@ reindex_index(Oid indexId, bool skip_constraint_checks)
27872801
* We can also reset indcheckxmin, because we have now done a
27882802
* non-concurrent index build, *except* in the case where index_build
27892803
* found some still-broken HOT chains.
2804+
*
2805+
* Note that it is important to not update the pg_index entry if we don't
2806+
* have to, because updating it will move the index's usability horizon
2807+
* (recorded as the tuple's xmin value) if indcheckxmin is true. We don't
2808+
* really want REINDEX to move the usability horizon forward ever, but we
2809+
* have no choice if we are to fix indisvalid or indisready. Of course,
2810+
* clearing indcheckxmin eliminates the issue, so we're happy to do that
2811+
* if we can. Another reason for caution here is that while reindexing
2812+
* pg_index itself, we must not try to update it. We assume that
2813+
* pg_index's indexes will always have these flags in their clean state.
27902814
*/
27912815
if (!skipped_constraint)
27922816
{

‎src/backend/commands/cluster.c

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1398,6 +1398,12 @@ finish_heap_swap(Oid OIDOldHeap, Oid OIDNewHeap,
13981398
* advantage to the other order anyway because this is all transactional,
13991399
* so no chance to reclaim disk space before commit. We do not need a
14001400
* final CommandCounterIncrement() because reindex_relation does it.
1401+
*
1402+
* Note: because index_build is called via reindex_relation, it will never
1403+
* set indcheckxmin true for the indexes. This is OK even though in some
1404+
* sense we are building new indexes rather than rebuilding existing ones,
1405+
* because the new heap won't contain any HOT chains at all, let alone
1406+
* broken ones, so it can't be necessary to set indcheckxmin.
14011407
*/
14021408
reindex_flags=REINDEX_REL_SUPPRESS_INDEX_USE;
14031409
if (check_constraints)

‎src/backend/commands/indexcmds.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -505,7 +505,7 @@ DefineIndex(RangeVar *heapRelation,
505505
indexInfo->ii_BrokenHotChain= false;
506506

507507
/* Now build the index */
508-
index_build(rel,indexRelation,indexInfo,primary);
508+
index_build(rel,indexRelation,indexInfo,primary, false);
509509

510510
/* Close both the relations, but keep the locks */
511511
heap_close(rel,NoLock);

‎src/include/catalog/index.h

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -75,7 +75,8 @@ extern void FormIndexDatum(IndexInfo *indexInfo,
7575
externvoidindex_build(RelationheapRelation,
7676
RelationindexRelation,
7777
IndexInfo*indexInfo,
78-
boolisprimary);
78+
boolisprimary,
79+
boolisreindex);
7980

8081
externdoubleIndexBuildHeapScan(RelationheapRelation,
8182
RelationindexRelation,

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