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Avoid redundant relation lock grabs during planning, and make sure

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that we acquire a lock on relations added to the query due to inheritance.
Formerly, no such lock was held throughout planning, which meant that
a schema change could occur to invalidate the plan before it's even
been completed.
This commit is contained in:
Tom Lane
2005-05-23 03:01:14 +00:00
parent 353f111f98
commit c1393173aa
3 changed files with 40 additions and 21 deletions
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31
src/backend/optimizer/util/plancat.c
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@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.107 2005/05/22 22:30:20 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.108 2005/05/23 03:01:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -67,7 +67,25 @@ get_relation_info(Oid relationObjectId, RelOptInfo *rel)
bool hasindex;
List *indexinfos = NIL;
relation = heap_open(relationObjectId, AccessShareLock);
/*
* Normally, we can assume the rewriter already acquired at least
* AccessShareLock on each relation used in the query. However this
* will not be the case for relations added to the query because they
* are inheritance children of some relation mentioned explicitly.
* For them, this is the first access during the parse/rewrite/plan
* pipeline, and so we need to obtain and keep a suitable lock.
*
* XXX really, a suitable lock is RowShareLock if the relation is
* an UPDATE/DELETE target, and AccessShareLock otherwise. However
* we cannot easily tell here which to get, so for the moment just
* get AccessShareLock always. The executor will get the right lock
* when it runs, which means there is a very small chance of deadlock
* trying to upgrade our lock.
*/
if (rel->reloptkind == RELOPT_BASEREL)
relation = heap_open(relationObjectId, NoLock);
else
relation = heap_open(relationObjectId, AccessShareLock);
rel->min_attr = FirstLowInvalidHeapAttributeNumber + 1;
rel->max_attr = RelationGetNumberOfAttributes(relation);
@@ -205,8 +223,8 @@ get_relation_info(Oid relationObjectId, RelOptInfo *rel)
rel->indexlist = indexinfos;
/* XXX keep the lock here? */
heap_close(relation, AccessShareLock);
/* close rel, but keep lock if any */
heap_close(relation, NoLock);
}
/*
@@ -374,7 +392,8 @@ build_physical_tlist(Query *root, RelOptInfo *rel)
switch (rte->rtekind)
{
case RTE_RELATION:
relation = heap_open(rte->relid, AccessShareLock);
/* Assume we already have adequate lock */
relation = heap_open(rte->relid, NoLock);
numattrs = RelationGetNumberOfAttributes(relation);
for (attrno = 1; attrno <= numattrs; attrno++)
@@ -401,7 +420,7 @@ build_physical_tlist(Query *root, RelOptInfo *rel)
false));
}
heap_close(relation, AccessShareLock);
heap_close(relation, NoLock);
break;
case RTE_SUBQUERY: