From 2cd0acfdade82f3cab362fd9129d453f81cc2745 Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Mon, 13 Aug 2018 08:22:18 +0530 Subject: [PATCH] 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 b797d064b7..c583e020a0 100644 --- a/src/backend/executor/execMain.c +++ b/src/backend/executor/execMain.c @@ -1726,8 +1726,12 @@ 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; } @@ -1773,8 +1777,12 @@ 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 66ea6aa3c3..bb28cf7d1d 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; } -- 2.40.0