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Commit7a21306

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Cope with inplace update making catcache stale during TOAST fetch.
This extendsad98fb1 to invals ofinplace updates. Trouble requires an inplace update of a catalog havinga TOAST table, so only pg_database was at risk. (The other catalog onwhich core code performs inplace updates, pg_class, has no TOAST table.)Trouble would require something like the inplace-inval.spec test.Consider GRANT ... ON DATABASE fetching a stale row from cache anddiscarding a datfrozenxid update that vac_truncate_clog() has alreadyrelied upon. Back-patch to v12 (all supported versions).Reviewed (in an earlier version) by Robert Haas.Discussion:https://postgr.es/m/20240114201411.d0@rfd.leadboat.comDiscussion:https://postgr.es/m/20240512232923.aa.nmisch@google.com
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3 files changed

+64
-3
lines changed

3 files changed

+64
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lines changed

‎src/backend/catalog/catalog.c

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -130,6 +130,27 @@ IsCatalogRelationOid(Oid relid)
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return (relid< (Oid)FirstBootstrapObjectId);
131131
}
132132

133+
/*
134+
* IsInplaceUpdateRelation
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*True iff core code performs inplace updates on the relation.
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*/
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bool
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IsInplaceUpdateRelation(Relationrelation)
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{
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returnIsInplaceUpdateOid(RelationGetRelid(relation));
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}
142+
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/*
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* IsInplaceUpdateOid
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*Like the above, but takes an OID as argument.
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*/
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bool
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IsInplaceUpdateOid(Oidrelid)
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{
150+
return (relid==RelationRelationId||
151+
relid==DatabaseRelationId);
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}
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133154
/*
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* IsToastRelation
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*True iff relation is a TOAST support relation (or index).

‎src/backend/utils/cache/catcache.c

Lines changed: 41 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,7 @@
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#include"access/table.h"
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#include"access/valid.h"
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#include"access/xact.h"
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#include"catalog/catalog.h"
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#include"catalog/pg_collation.h"
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#include"catalog/pg_operator.h"
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#include"catalog/pg_type.h"
@@ -1847,6 +1848,23 @@ ReleaseCatCacheList(CatCList *list)
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}
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18491850

1851+
/*
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* equalTuple
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*Are these tuples memcmp()-equal?
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*/
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staticbool
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equalTuple(HeapTuplea,HeapTupleb)
1857+
{
1858+
uint32alen;
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uint32blen;
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1861+
alen=a->t_len;
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blen=b->t_len;
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return (alen==blen&&
1864+
memcmp((char*)a->t_data,
1865+
(char*)b->t_data,blen)==0);
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}
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/*
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* CatalogCacheCreateEntry
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*Create a new CatCTup entry, copying the given HeapTuple and other
@@ -1897,14 +1915,34 @@ CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp, SysScanDesc scandesc,
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*/
18981916
if (HeapTupleHasExternal(ntp))
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{
1918+
boolneed_cmp=IsInplaceUpdateOid(cache->cc_reloid);
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HeapTuplebefore=NULL;
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boolmatches= true;
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1922+
if (need_cmp)
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before=heap_copytuple(ntp);
19001924
dtp=toast_flatten_tuple(ntp,cache->cc_tupdesc);
19011925

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/*
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* The tuple could become stale while we are doing toast table
1904-
* access (since AcceptInvalidationMessages can run then), so we
1905-
* must recheck its visibility afterwards.
1928+
* access (since AcceptInvalidationMessages can run then).
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* equalTuple() detects staleness from inplace updates, while
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* systable_recheck_tuple() detects staleness from normal updates.
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*
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* While this equalTuple() follows the usual rule of reading with
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* a pin and no buffer lock, it warrants suspicion since an
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* inplace update could appear at any moment. It's safe because
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* the inplace update sends an invalidation that can't reorder
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* before the inplace heap change. If the heap change reaches
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* this process just after equalTuple() looks, we've not missed
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* its inval.
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*/
1907-
if (!systable_recheck_tuple(scandesc,ntp))
1940+
if (need_cmp)
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{
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matches=equalTuple(before,ntp);
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heap_freetuple(before);
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}
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if (!matches|| !systable_recheck_tuple(scandesc,ntp))
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{
19091947
heap_freetuple(dtp);
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returnNULL;

‎src/include/catalog/catalog.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,11 +21,13 @@
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externboolIsSystemRelation(Relationrelation);
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externboolIsToastRelation(Relationrelation);
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externboolIsCatalogRelation(Relationrelation);
24+
externboolIsInplaceUpdateRelation(Relationrelation);
2425

2526
externboolIsSystemClass(Oidrelid,Form_pg_classreltuple);
2627
externboolIsToastClass(Form_pg_classreltuple);
2728

2829
externboolIsCatalogRelationOid(Oidrelid);
30+
externboolIsInplaceUpdateOid(Oidrelid);
2931

3032
externboolIsCatalogNamespace(OidnamespaceId);
3133
externboolIsToastNamespace(OidnamespaceId);

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