From ceba1dacea54779c397bfcb68a48f7e7defe0ce6 Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Sun, 5 Aug 2018 11:33:51 +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 01e1a46..0a58688 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 66ea6aa..bb28cf7 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; } -- 1.8.3.1