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For inplace update durability, make heap_update() callers wait.

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The previous commit fixed some ways of losing an inplace update.  It
remained possible to lose one when a backend working toward a
heap_update() copied a tuple into memory just before inplace update of
that tuple.  In catalogs eligible for inplace update, use LOCKTAG_TUPLE
to govern admission to the steps of copying an old tuple, modifying it,
and issuing heap_update().  This includes MERGE commands.  To avoid
changing most of the pg_class DDL, don't require LOCKTAG_TUPLE when
holding a relation lock sufficient to exclude inplace updaters.
Back-patch to v12 (all supported versions).  In v13 and v12, "UPDATE
pg_class" or "UPDATE pg_database" can still lose an inplace update.  The
v14+ UPDATE fix needs commit 86dc90056d,
and it wasn't worth reimplementing that fix without such infrastructure.

Reviewed by Nitin Motiani and (in earlier versions) Heikki Linnakangas.

Discussion: https://postgr.es/m/20231027214946.79.nmisch@google.com
This commit is contained in:
Noah Misch
2024-09-24 15:25:18 -07:00
parent a07e03fd8f
commit aac2c9b4fd
20 changed files with 498 additions and 57 deletions
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9
src/backend/utils/cache/relcache.c vendored
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@@ -3768,6 +3768,7 @@ RelationSetNewRelfilenumber(Relation relation, char persistence)
{
RelFileNumber newrelfilenumber;
Relation pg_class;
ItemPointerData otid;
HeapTuple tuple;
Form_pg_class classform;
MultiXactId minmulti = InvalidMultiXactId;
@@ -3810,11 +3811,12 @@ RelationSetNewRelfilenumber(Relation relation, char persistence)
*/
pg_class = table_open(RelationRelationId, RowExclusiveLock);
tuple = SearchSysCacheCopy1(RELOID,
ObjectIdGetDatum(RelationGetRelid(relation)));
tuple = SearchSysCacheLockedCopy1(RELOID,
ObjectIdGetDatum(RelationGetRelid(relation)));
if (!HeapTupleIsValid(tuple))
elog(ERROR, "could not find tuple for relation %u",
RelationGetRelid(relation));
otid = tuple->t_self;
classform = (Form_pg_class) GETSTRUCT(tuple);
/*
@@ -3934,9 +3936,10 @@ RelationSetNewRelfilenumber(Relation relation, char persistence)
classform->relminmxid = minmulti;
classform->relpersistence = persistence;
CatalogTupleUpdate(pg_class, &tuple->t_self, tuple);
CatalogTupleUpdate(pg_class, &otid, tuple);
}
UnlockTuple(pg_class, &otid, InplaceUpdateTupleLock);
heap_freetuple(tuple);
table_close(pg_class, RowExclusiveLock);