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Push tuple limits through Gather and Gather Merge.

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If we only need, say, 10 tuples in total, then we certainly don't need
more than 10 tuples from any single process.  Pushing down the limit
lets workers exit early when possible.  For Gather Merge, there is
an additional benefit: a Sort immediately below the Gather Merge can
be done as a bounded sort if there is an applicable limit.

Robert Haas and Tom Lane

Discussion: http://postgr.es/m/CA+TgmoYa3QKKrLj5rX7UvGqhH73G1Li4B-EKxrmASaca2tFu9Q@mail.gmail.com
This commit is contained in:
Robert Haas
2017-08-29 13:12:23 -04:00
parent ce5dcf54b9
commit 3452dc5240
10 changed files with 222 additions and 97 deletions
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src/include/executor/executor.h
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@ -232,6 +232,7 @@ extern PlanState *ExecInitNode(Plan *node, EState *estate, int eflags);
extern Node *MultiExecProcNode(PlanState *node);
extern void ExecEndNode(PlanState *node);
extern bool ExecShutdownNode(PlanState *node);
extern void ExecSetTupleBound(int64 tuples_needed, PlanState *child_node);
/* ----------------------------------------------------------------