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Fix problems with cached tuple descriptors disappearing while still in use

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by creating a reference-count mechanism, similar to what we did a long time
ago for catcache entries.  The back branches have an ugly solution involving
lots of extra copies, but this way is more efficient.  Reference counting is
only applied to tupdescs that are actually in caches --- there seems no need
to use it for tupdescs that are generated in the executor, since they'll go
away during plan shutdown by virtue of being in the per-query memory context.
Neil Conway and Tom Lane
This commit is contained in:
Tom Lane
2006-06-16 18:42:24 +00:00
parent b49ce32da1
commit 06e10abc0b
36 changed files with 581 additions and 246 deletions
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31
src/backend/utils/cache/relcache.c vendored
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.241 2006/05/06 15:51:07 tgl Exp $
* $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.242 2006/06/16 18:42:22 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -313,6 +313,8 @@ AllocateRelationDesc(Relation relation, Form_pg_class relp)
/* and allocate attribute tuple form storage */
relation->rd_att = CreateTemplateTupleDesc(relationForm->relnatts,
relationForm->relhasoids);
/* which we mark as a reference-counted tupdesc */
relation->rd_att->tdrefcount = 1;
MemoryContextSwitchTo(oldcxt);
@ -1234,6 +1236,8 @@ formrdesc(const char *relationName, Oid relationReltype,
* defined by macros in src/include/catalog/ headers.
*/
relation->rd_att = CreateTemplateTupleDesc(natts, hasoids);
relation->rd_att->tdrefcount = 1; /* mark as refcounted */
relation->rd_att->tdtypeid = relationReltype;
relation->rd_att->tdtypmod = -1; /* unnecessary, but... */
@ -1591,7 +1595,10 @@ RelationClearRelation(Relation relation, bool rebuild)
{
/* ok to zap remaining substructure */
flush_rowtype_cache(old_reltype);
FreeTupleDesc(relation->rd_att);
/* can't use DecrTupleDescRefCount here */
Assert(relation->rd_att->tdrefcount > 0);
if (--relation->rd_att->tdrefcount == 0)
FreeTupleDesc(relation->rd_att);
if (relation->rd_rulescxt)
MemoryContextDelete(relation->rd_rulescxt);
pfree(relation);
@ -1601,7 +1608,10 @@ RelationClearRelation(Relation relation, bool rebuild)
/*
* When rebuilding an open relcache entry, must preserve ref count and
* rd_createSubid state. Also attempt to preserve the tupledesc and
* rewrite-rule substructures in place.
* rewrite-rule substructures in place. (Note: the refcount mechanism
* for tupledescs may eventually ensure that we don't really need to
* preserve the tupledesc in-place, but for now there are still a lot
* of places that assume an open rel's tupledesc won't move.)
*
* Note that this process does not touch CurrentResourceOwner; which
* is good because whatever ref counts the entry may have do not
@ -1618,7 +1628,9 @@ RelationClearRelation(Relation relation, bool rebuild)
{
/* Should only get here if relation was deleted */
flush_rowtype_cache(old_reltype);
FreeTupleDesc(old_att);
Assert(old_att->tdrefcount > 0);
if (--old_att->tdrefcount == 0)
FreeTupleDesc(old_att);
if (old_rulescxt)
MemoryContextDelete(old_rulescxt);
pfree(relation);
@ -1629,13 +1641,17 @@ RelationClearRelation(Relation relation, bool rebuild)
if (equalTupleDescs(old_att, relation->rd_att))
{
/* needn't flush typcache here */
FreeTupleDesc(relation->rd_att);
Assert(relation->rd_att->tdrefcount == 1);
if (--relation->rd_att->tdrefcount == 0)
FreeTupleDesc(relation->rd_att);
relation->rd_att = old_att;
}
else
{
flush_rowtype_cache(old_reltype);
FreeTupleDesc(old_att);
Assert(old_att->tdrefcount > 0);
if (--old_att->tdrefcount == 0)
FreeTupleDesc(old_att);
}
if (equalRuleLocks(old_rules, relation->rd_rules))
{
@ -2075,6 +2091,7 @@ RelationBuildLocalRelation(const char *relname,
* catalogs. We can copy attnotnull constraints here, however.
*/
rel->rd_att = CreateTupleDescCopy(tupDesc);
rel->rd_att->tdrefcount = 1; /* mark as refcounted */
has_not_null = false;
for (i = 0; i < natts; i++)
{
@ -2996,6 +3013,8 @@ load_relcache_init_file(void)
/* initialize attribute tuple forms */
rel->rd_att = CreateTemplateTupleDesc(relform->relnatts,
relform->relhasoids);
rel->rd_att->tdrefcount = 1; /* mark as refcounted */
rel->rd_att->tdtypeid = relform->reltype;
rel->rd_att->tdtypmod = -1; /* unnecessary, but... */