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Commitb805b63

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author
Amit Kapila
committed
Fix buffer usage stats for parallel nodes.
The buffer usage stats is accounted only for the execution phase of thenode. For Gather and Gather Merge nodes, such stats are accumulated atthe time of shutdown of workers which is done after execution of node dueto which we missed to account them for such nodes. Fix it by treatingnodes as running while we shut down them.We can also miss accounting for a Limit node when Gather or Gather Mergeis beneath it, because it can finish the execution before shutting downsuch nodes. So we allow a Limit node to shut down the resources before itcompletes the execution.In the passing fix the gather node code to allow workers to shut down assoon as we find that all the tuples from the workers have been retrieved.The original code use to do that, but is accidently removed by commit01edb5c.Reported-by: Adrien NayratAuthor: Amit Kapila and Robert HaasReviewed-by: Robert Haas and Andres FreundBackpatch-through: 9.6 where this code was introducedDiscussion:https://postgr.es/m/86137f17-1dfb-42f9-7421-82fd786b04a1@anayrat.info
1 parent3f02b51 commitb805b63

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3 files changed

+22
-0
lines changed

3 files changed

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lines changed

‎src/backend/executor/execProcnode.c

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Original file line numberDiff line numberDiff line change
@@ -737,6 +737,19 @@ ExecShutdownNode(PlanState *node)
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planstate_tree_walker(node,ExecShutdownNode,NULL);
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/*
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* Treat the node as running while we shut it down, but only if it's run
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* at least once already. We don't expect much CPU consumption during
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* node shutdown, but in the case of Gather or Gather Merge, we may shut
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* down workers at this stage. If so, their buffer usage will get
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* propagated into pgBufferUsage at this point, and we want to make sure
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* that it gets associated with the Gather node. We skip this if the node
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* has never been executed, so as to avoid incorrectly making it appear
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* that it has.
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*/
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if (node->instrument&&node->instrument->running)
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InstrStartNode(node->instrument);
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switch (nodeTag(node))
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{
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caseT_GatherState:
@@ -755,5 +768,9 @@ ExecShutdownNode(PlanState *node)
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break;
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}
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/* Stop the node if we started it above, reporting 0 tuples. */
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if (node->instrument&&node->instrument->running)
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InstrStopNode(node->instrument,0);
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return false;
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}

‎src/backend/executor/nodeGather.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -327,7 +327,10 @@ gather_readnext(GatherState *gatherstate)
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Assert(!tup);
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--gatherstate->nreaders;
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if (gatherstate->nreaders==0)
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{
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ExecShutdownGatherWorkers(gatherstate);
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returnNULL;
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}
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memmove(&gatherstate->reader[gatherstate->nextreader],
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&gatherstate->reader[gatherstate->nextreader+1],
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sizeof(TupleQueueReader*)

‎src/backend/executor/nodeLimit.c

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Original file line numberDiff line numberDiff line change
@@ -134,6 +134,8 @@ ExecLimit(PlanState *pstate)
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node->position-node->offset >=node->count)
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{
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node->lstate=LIMIT_WINDOWEND;
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/* Allow nodes to release or shut down resources. */
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(void)ExecShutdownNode(outerPlan);
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returnNULL;
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}
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