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Commite4afd71

Browse files
committed
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 parentfc8c258 commite4afd71

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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
@@ -137,6 +137,27 @@ IsCatalogRelationOid(Oid relid)
137137
return (relid< (Oid)FirstUnpinnedObjectId);
138138
}
139139

140+
/*
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* IsInplaceUpdateRelation
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*True iff core code performs inplace updates on the relation.
143+
*/
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bool
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IsInplaceUpdateRelation(Relationrelation)
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{
147+
returnIsInplaceUpdateOid(RelationGetRelid(relation));
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}
149+
150+
/*
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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)
156+
{
157+
return (relid==RelationRelationId||
158+
relid==DatabaseRelationId);
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}
160+
140161
/*
141162
* IsToastRelation
142163
*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
@@ -20,6 +20,7 @@
2020
#include"access/sysattr.h"
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#include"access/table.h"
2222
#include"access/xact.h"
23+
#include"catalog/catalog.h"
2324
#include"catalog/pg_collation.h"
2425
#include"catalog/pg_operator.h"
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#include"catalog/pg_type.h"
@@ -1938,6 +1939,23 @@ ReleaseCatCacheList(CatCList *list)
19381939
}
19391940

19401941

1942+
/*
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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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{
1949+
uint32alen;
1950+
uint32blen;
1951+
1952+
alen=a->t_len;
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blen=b->t_len;
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return (alen==blen&&
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memcmp((char*)a->t_data,
1956+
(char*)b->t_data,blen)==0);
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}
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19411959
/*
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* CatalogCacheCreateEntry
19431961
*Create a new CatCTup entry, copying the given HeapTuple and other
@@ -1988,14 +2006,34 @@ CatalogCacheCreateEntry(CatCache *cache, HeapTuple ntp, SysScanDesc scandesc,
19882006
*/
19892007
if (HeapTupleHasExternal(ntp))
19902008
{
2009+
boolneed_cmp=IsInplaceUpdateOid(cache->cc_reloid);
2010+
HeapTuplebefore=NULL;
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boolmatches= true;
2012+
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if (need_cmp)
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before=heap_copytuple(ntp);
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dtp=toast_flatten_tuple(ntp,cache->cc_tupdesc);
19922016

19932017
/*
19942018
* The tuple could become stale while we are doing toast table
1995-
* access (since AcceptInvalidationMessages can run then), so we
1996-
* must recheck its visibility afterwards.
2019+
* access (since AcceptInvalidationMessages can run then).
2020+
* equalTuple() detects staleness from inplace updates, while
2021+
* 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
2024+
* a pin and no buffer lock, it warrants suspicion since an
2025+
* inplace update could appear at any moment. It's safe because
2026+
* the inplace update sends an invalidation that can't reorder
2027+
* before the inplace heap change. If the heap change reaches
2028+
* this process just after equalTuple() looks, we've not missed
2029+
* its inval.
19972030
*/
1998-
if (!systable_recheck_tuple(scandesc,ntp))
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if (need_cmp)
2032+
{
2033+
matches=equalTuple(before,ntp);
2034+
heap_freetuple(before);
2035+
}
2036+
if (!matches|| !systable_recheck_tuple(scandesc,ntp))
19992037
{
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heap_freetuple(dtp);
20012039
returnNULL;

‎src/include/catalog/catalog.h‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,11 +21,13 @@
2121
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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