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Commitf9f47f0

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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
1 parent5b823b1 commitf9f47f0

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3 files changed

+64
-3
lines changed

3 files changed

+64
-3
lines changed

‎src/backend/catalog/catalog.c

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -135,6 +135,27 @@ IsCatalogRelationOid(Oid relid)
135135
return (relid< (Oid)FirstUnpinnedObjectId);
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}
137137

138+
/*
139+
* 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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}
147+
148+
/*
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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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{
155+
return (relid==RelationRelationId||
156+
relid==DatabaseRelationId);
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}
158+
138159
/*
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* IsToastRelation
140161
*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
@@ -19,6 +19,7 @@
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#include"access/relscan.h"
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#include"access/table.h"
2121
#include"access/xact.h"
22+
#include"catalog/catalog.h"
2223
#include"catalog/pg_collation.h"
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#include"catalog/pg_type.h"
2425
#include"common/hashfn.h"
@@ -2007,6 +2008,23 @@ ReleaseCatCacheListWithOwner(CatCList *list, ResourceOwner resowner)
20072008
}
20082009

20092010

2011+
/*
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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)
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{
2018+
uint32alen;
2019+
uint32blen;
2020+
2021+
alen=a->t_len;
2022+
blen=b->t_len;
2023+
return (alen==blen&&
2024+
memcmp((char*)a->t_data,
2025+
(char*)b->t_data,blen)==0);
2026+
}
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20102028
/*
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* CatalogCacheCreateEntry
20122030
*Create a new CatCTup entry, copying the given HeapTuple and other
@@ -2057,14 +2075,34 @@ CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp, SysScanDesc scandesc,
20572075
*/
20582076
if (HeapTupleHasExternal(ntp))
20592077
{
2078+
boolneed_cmp=IsInplaceUpdateOid(cache->cc_reloid);
2079+
HeapTuplebefore=NULL;
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boolmatches= true;
2081+
2082+
if (need_cmp)
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before=heap_copytuple(ntp);
20602084
dtp=toast_flatten_tuple(ntp,cache->cc_tupdesc);
20612085

20622086
/*
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* The tuple could become stale while we are doing toast table
2064-
* access (since AcceptInvalidationMessages can run then), so we
2065-
* must recheck its visibility afterwards.
2088+
* 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
2097+
* this process just after equalTuple() looks, we've not missed
2098+
* its inval.
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*/
2067-
if (!systable_recheck_tuple(scandesc,ntp))
2100+
if (need_cmp)
2101+
{
2102+
matches=equalTuple(before,ntp);
2103+
heap_freetuple(before);
2104+
}
2105+
if (!matches|| !systable_recheck_tuple(scandesc,ntp))
20682106
{
20692107
heap_freetuple(dtp);
20702108
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);
2323
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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