Revert "Don't lock partitions pruned by initial pruning"

As pointed out by Tom Lane, the patch introduced fragile and invasive
design around plan invalidation handling when locking of prunable
partitions was deferred from plancache.c to the executor. In
particular, it violated assumptions about CachedPlan immutability and
altered executor APIs in ways that are difficult to justify given the
added complexity and overhead.

This also removes the firstResultRels field added to PlannedStmt in
commit 28317de72, which was intended to support deferred locking of
certain ModifyTable result relations.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/605328.1747710381@sss.pgh.pa.us

1 files changed, 2 insertions, 64 deletions

diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index 3f8a4cb5244..514eae1037d 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -26,7 +26,6 @@
 #include "partitioning/partdesc.h"
 #include "partitioning/partprune.h"
 #include "rewrite/rewriteManip.h"
-#include "storage/lmgr.h"
 #include "utils/acl.h"
 #include "utils/lsyscache.h"
 #include "utils/partcache.h"
@@ -1771,8 +1770,7 @@ adjust_partition_colnos_using_map(List *colnos, AttrMap *attrMap)
  * ExecDoInitialPruning:
  *		Perform runtime "initial" pruning, if necessary, to determine the set
  *		of child subnodes that need to be initialized during ExecInitNode() for
- *		all plan nodes that contain a PartitionPruneInfo.  This also locks the
- *		leaf partitions whose subnodes will be initialized if needed.
+ *		all plan nodes that contain a PartitionPruneInfo.
  *
  * ExecInitPartitionExecPruning:
  *		Updates the PartitionPruneState found at given part_prune_index in
@@ -1798,8 +1796,7 @@ adjust_partition_colnos_using_map(List *colnos, AttrMap *attrMap)
  * ExecDoInitialPruning
  *		Perform runtime "initial" pruning, if necessary, to determine the set
  *		of child subnodes that need to be initialized during ExecInitNode() for
- *		plan nodes that support partition pruning.  This also locks the leaf
- *		partitions whose subnodes will be initialized if needed.
+ *		plan nodes that support partition pruning.
  *
  * This function iterates over each PartitionPruneInfo entry in
  * estate->es_part_prune_infos. For each entry, it creates a PartitionPruneState
@@ -1821,9 +1818,7 @@ adjust_partition_colnos_using_map(List *colnos, AttrMap *attrMap)
 void
 ExecDoInitialPruning(EState *estate)
 {
-	PlannedStmt *stmt = estate->es_plannedstmt;
 	ListCell   *lc;
-	List	   *locked_relids = NIL;
 
 	foreach(lc, estate->es_part_prune_infos)
 	{
@@ -1849,68 +1844,11 @@ ExecDoInitialPruning(EState *estate)
 		else
 			validsubplan_rtis = all_leafpart_rtis;
 
-		if (ExecShouldLockRelations(estate))
-		{
-			int			rtindex = -1;
-
-			while ((rtindex = bms_next_member(validsubplan_rtis,
-											  rtindex)) >= 0)
-			{
-				RangeTblEntry *rte = exec_rt_fetch(rtindex, estate);
-
-				Assert(rte->rtekind == RTE_RELATION &&
-					   rte->rellockmode != NoLock);
-				LockRelationOid(rte->relid, rte->rellockmode);
-				locked_relids = lappend_int(locked_relids, rtindex);
-			}
-		}
 		estate->es_unpruned_relids = bms_add_members(estate->es_unpruned_relids,
 													 validsubplan_rtis);
 		estate->es_part_prune_results = lappend(estate->es_part_prune_results,
 												validsubplans);
 	}
-
-	/*
-	 * Lock the first result relation of each ModifyTable node, even if it was
-	 * pruned.  This is required for ExecInitModifyTable(), which keeps its
-	 * first result relation if all other result relations have been pruned,
-	 * because some executor paths (e.g., in nodeModifyTable.c and
-	 * execPartition.c) rely on there being at least one result relation.
-	 *
-	 * There's room for improvement here --- we actually only need to do this
-	 * if all other result relations of the ModifyTable node were pruned, but
-	 * we don't have an easy way to tell that here.
-	 */
-	if (stmt->resultRelations && ExecShouldLockRelations(estate))
-	{
-		foreach(lc, stmt->firstResultRels)
-		{
-			Index		firstResultRel = lfirst_int(lc);
-
-			if (!bms_is_member(firstResultRel, estate->es_unpruned_relids))
-			{
-				RangeTblEntry *rte = exec_rt_fetch(firstResultRel, estate);
-
-				Assert(rte->rtekind == RTE_RELATION && rte->rellockmode != NoLock);
-				LockRelationOid(rte->relid, rte->rellockmode);
-				locked_relids = lappend_int(locked_relids, firstResultRel);
-			}
-		}
-	}
-
-	/*
-	 * Release the useless locks if the plan won't be executed.  This is the
-	 * same as what CheckCachedPlan() in plancache.c does.
-	 */
-	if (!ExecPlanStillValid(estate))
-	{
-		foreach(lc, locked_relids)
-		{
-			RangeTblEntry *rte = exec_rt_fetch(lfirst_int(lc), estate);
-
-			UnlockRelationOid(rte->relid, rte->rellockmode);
-		}
-	}
 }
 
 /*