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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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7
src/backend/commands/event_trigger.c
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@@ -388,6 +388,7 @@ SetDatabaseHasLoginEventTriggers(void)
/* Set dathasloginevt flag in pg_database */
Form_pg_database db;
Relation pg_db = table_open(DatabaseRelationId, RowExclusiveLock);
ItemPointerData otid;
HeapTuple tuple;
/*
@@ -399,16 +400,18 @@ SetDatabaseHasLoginEventTriggers(void)
*/
LockSharedObject(DatabaseRelationId, MyDatabaseId, 0, AccessExclusiveLock);
tuple = SearchSysCacheCopy1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
tuple = SearchSysCacheLockedCopy1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
if (!HeapTupleIsValid(tuple))
elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
otid = tuple->t_self;
db = (Form_pg_database) GETSTRUCT(tuple);
if (!db->dathasloginevt)
{
db->dathasloginevt = true;
CatalogTupleUpdate(pg_db, &tuple->t_self, tuple);
CatalogTupleUpdate(pg_db, &otid, tuple);
CommandCounterIncrement();
}
UnlockTuple(pg_db, &otid, InplaceUpdateTupleLock);
table_close(pg_db, RowExclusiveLock);
heap_freetuple(tuple);
}