postgres.git / summary / log / commit / refs

commit    ba10eaef509bf47de743589a232e83f071acf8dc
Author:   Amit Kapila <akapila@postgresql.org>
Date:     Mon Aug 13 03:13:33 2018 +0000

    Prohibit shutting down resources if there is a possibility of back up.
    
    Currently, we release the asynchronous resources as soon as it is evident
    that no more rows will be needed e.g. when a Limit is filled.  This can be
    problematic especially for custom and foreign scans where we can scan
    backward.  Fix that by disallowing the shutting down of resources in such
    cases.
    
    Reported-by: Robert Haas
    Analysed-by: Robert Haas and Amit Kapila
    Author: Amit Kapila
    Reviewed-by: Robert Haas
    Backpatch-through: 9.6 where this code was introduced
    Discussion: https://postgr.es/m/86137f17-1dfb-42f9-7421-82fd786b04a1@anayrat.info


 src/backend/executor/execMain.c  | 16 ++++++++++++----
 src/backend/executor/nodeLimit.c | 10 ++++++++--
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 878e8e9ea13..6f467c65c10 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -1727,8 +1727,12 @@ ExecutePlan(EState *estate,
 		 */
 		if (TupIsNull(slot))
 		{
-			/* Allow nodes to release or shut down resources. */
-			(void) ExecShutdownNode(planstate);
+			/*
+			 * If we know we won't need to back up, we can release
+			 * resources at this point.
+			 */
+			if (!(estate->es_top_eflags & EXEC_FLAG_BACKWARD))
+				(void) ExecShutdownNode(planstate);
 			break;
 		}
 
@@ -1774,8 +1778,12 @@ ExecutePlan(EState *estate,
 		current_tuple_count++;
 		if (numberTuples && numberTuples == current_tuple_count)
 		{
-			/* Allow nodes to release or shut down resources. */
-			(void) ExecShutdownNode(planstate);
+			/*
+			 * If we know we won't need to back up, we can release
+			 * resources at this point.
+			 */
+			if (!(estate->es_top_eflags & EXEC_FLAG_BACKWARD))
+				(void) ExecShutdownNode(planstate);
 			break;
 		}
 	}
diff --git a/src/backend/executor/nodeLimit.c b/src/backend/executor/nodeLimit.c
index cf1851e235f..6e74bb23d06 100644
--- a/src/backend/executor/nodeLimit.c
+++ b/src/backend/executor/nodeLimit.c
@@ -134,8 +134,14 @@ ExecLimit(PlanState *pstate)
 					node->position - node->offset >= node->count)
 				{
 					node->lstate = LIMIT_WINDOWEND;
-					/* Allow nodes to release or shut down resources. */
-					(void) ExecShutdownNode(outerPlan);
+
+					/*
+					 * If we know we won't need to back up, we can release
+					 * resources at this point.
+					 */
+					if (!(node->ps.state->es_top_eflags & EXEC_FLAG_BACKWARD))
+						(void) ExecShutdownNode(outerPlan);
+
 					return NULL;
 				}
 


[parent: 556140424c4b]