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Commit947789f

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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.Per the lack of complaints on the matter, no backpatch is done. Notethat before96cdeae, attempting to insert such a tuple to pg_databasewould cause a "row is too big" error, so the end-of-vacuum problem wasnot reachable.Author: Ashwin Agrawal, Junfeng YangDiscussion:https://postgr.es/m/DM5PR0501MB38800D9E4605BCA72DD35557CCE10@DM5PR0501MB3880.namprd05.prod.outlook.com
1 parent0a665bb commit947789f

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2 files changed

+22
-2
lines changed

2 files changed

+22
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lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5710,6 +5710,10 @@ 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: 18 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1361,6 +1361,7 @@ 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
@@ -1479,10 +1480,25 @@ 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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1482-
/* 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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