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Commit72b6098

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Avoid using tuple from syscache for update of pg_database.datfrozenxid
pg_database.datfrozenxid gets updated using an in-place update at theend of vacuum or autovacuum. Since96cdeae, as pg_database has a toastrelation, it is possible for a pg_database tuple to have toast valuesif there is a large set of ACLs in place. In such a case, the in-placeupdate would fail because of the flattening of the toast values done forthe catcache entry fetched. Instead of using a copy from the catcache,this changes the logic to fetch the copy of the tuple by directlyscanning pg_database.Note that before96cdeae, attempting to insert such a tuple topg_database would cause a "row is too big" error, so the end-of-vacuumproblem was not reachable.This issue has been originally fixed in947789f on v14~, and there havebeen reports about this problem on v12 and v13, causing failures at theend of VACUUM. This completes the fix on all the stable branches wherepg_database can use a toast table, down to 12.Author: Ashwin Agrawal, Junfeng YangDiscussion:https://postgr.es/m/DM5PR0501MB38800D9E4605BCA72DD35557CCE10@DM5PR0501MB3880.namprd05.prod.outlook.comDiscussion:https://postgr.es/m/Y70XNVbUWQsR2Car@paquier.xyzBackpatch-through: 12
1 parent2ad4abe commit72b6098

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2 files changed

+23
-2
lines changed

2 files changed

+23
-2
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5806,6 +5806,10 @@ heap_abort_speculative(Relation relation, ItemPointer tid)
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*
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* tuple is an in-memory tuple structure containing the data to be written
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* over the target tuple. Also, tuple->t_self identifies the target tuple.
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*
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* Note that the tuple updated here had better not come directly from the
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* syscache if the relation has a toast relation as this tuple could
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* include toast values that have been expanded, causing a failure here.
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*/
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void
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heap_inplace_update(Relationrelation,HeapTupletuple)

‎src/backend/commands/vacuum.c

Lines changed: 19 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -31,6 +31,7 @@
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#include"access/tableam.h"
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#include"access/transam.h"
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#include"access/xact.h"
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#include"catalog/indexing.h"
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#include"catalog/namespace.h"
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#include"catalog/pg_database.h"
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#include"catalog/pg_inherits.h"
@@ -1343,6 +1344,7 @@ vac_update_datfrozenxid(void)
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MultiXactIdlastSaneMinMulti;
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boolbogus= false;
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booldirty= false;
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ScanKeyDatakey[1];
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/*
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* Restrict this task to one backend per database. This avoids race
@@ -1460,10 +1462,25 @@ vac_update_datfrozenxid(void)
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/* Now fetch the pg_database tuple we need to update. */
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relation=table_open(DatabaseRelationId,RowExclusiveLock);
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/* Fetch a copy of the tuple to scribble on */
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tuple=SearchSysCacheCopy1(DATABASEOID,ObjectIdGetDatum(MyDatabaseId));
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/*
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* Get the pg_database tuple to scribble on. Note that this does not
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* directly rely on the syscache to avoid issues with flattened toast
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* values for the in-place update.
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*/
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ScanKeyInit(&key[0],
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Anum_pg_database_oid,
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BTEqualStrategyNumber,F_OIDEQ,
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ObjectIdGetDatum(MyDatabaseId));
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scan=systable_beginscan(relation,DatabaseOidIndexId, true,
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NULL,1,key);
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tuple=systable_getnext(scan);
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tuple=heap_copytuple(tuple);
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systable_endscan(scan);
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if (!HeapTupleIsValid(tuple))
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elog(ERROR,"could not find tuple for database %u",MyDatabaseId);
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dbform= (Form_pg_database)GETSTRUCT(tuple);
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/*

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