Change rewriter/planner/executor/plancache to depend on RTE rellockmode.

Instead of recomputing the required lock levels in all these places,
just use what commit fdba460a2 made the parser store in the RTE fields.
This already simplifies the code measurably in these places, and
follow-on changes will remove a bunch of no-longer-needed infrastructure.

In a few cases, this change causes us to acquire a higher lock level
than we did before.  This is OK primarily because said higher lock level
should've been acquired already at query parse time; thus, we're saving
a useless extra trip through the shared lock manager to acquire a lesser
lock alongside the original lock.  The only known exception to this is
that re-execution of a previously planned SELECT FOR UPDATE/SHARE query,
for a table that uses ROW_MARK_REFERENCE or ROW_MARK_COPY methods, might
have gotten only AccessShareLock before.  Now it will get RowShareLock
like the first execution did, which seems fine.

While there's more to do, push it in this state anyway, to let the
buildfarm help verify that nothing bad happened.

Amit Langote, reviewed by David Rowley and Jesper Pedersen,
and whacked around a bit more by me

Discussion: https://postgr.es/m/468c85d9-540e-66a2-1dde-fec2b741e688@lab.ntt.co.jp

1 files changed, 3 insertions, 15 deletions

diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 690b6bbab7f..d5720518a81 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -1515,7 +1515,6 @@ expand_inherited_tables(PlannerInfo *root)
 static void
 expand_inherited_rtentry(PlannerInfo *root, RangeTblEntry *rte, Index rti)
 {
-	Query	   *parse = root->parse;
 	Oid			parentOID;
 	PlanRowMark *oldrc;
 	Relation	oldrelation;
@@ -1546,21 +1545,9 @@ expand_inherited_rtentry(PlannerInfo *root, RangeTblEntry *rte, Index rti)
 	 * relation named in the query.  However, for each child relation we add
 	 * to the query, we must obtain an appropriate lock, because this will be
 	 * the first use of those relations in the parse/rewrite/plan pipeline.
-	 *
-	 * If the parent relation is the query's result relation, then we need
-	 * RowExclusiveLock.  Otherwise, if it's accessed FOR UPDATE/SHARE, we
-	 * need RowShareLock; otherwise AccessShareLock.  We can't just grab
-	 * AccessShareLock because then the executor would be trying to upgrade
-	 * the lock, leading to possible deadlocks.  (This code should match the
-	 * parser and rewriter.)
+	 * Child rels should use the same lockmode as their parent.
 	 */
-	oldrc = get_plan_rowmark(root->rowMarks, rti);
-	if (rti == parse->resultRelation)
-		lockmode = RowExclusiveLock;
-	else if (oldrc && RowMarkRequiresRowShareLock(oldrc->markType))
-		lockmode = RowShareLock;
-	else
-		lockmode = AccessShareLock;
+	lockmode = rte->rellockmode;
 
 	/* Scan for all members of inheritance set, acquire needed locks */
 	inhOIDs = find_all_inheritors(parentOID, lockmode, NULL);
@@ -1582,6 +1569,7 @@ expand_inherited_rtentry(PlannerInfo *root, RangeTblEntry *rte, Index rti)
 	 * PlanRowMark as isParent = true, and generate a new PlanRowMark for each
 	 * child.
 	 */
+	oldrc = get_plan_rowmark(root->rowMarks, rti);
 	if (oldrc)
 		oldrc->isParent = true;