Push tuple limits through Gather and Gather Merge.
Robert Haas <rhaas@postgresql.org>
Push tuple limits through Gather and Gather Merge. 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
Files
| Path | Change | +/− |
|---|---|---|
| src/backend/executor/execParallel.c | modified | +44 −10 |
| src/backend/executor/execProcnode.c | modified | +121 −0 |
| src/backend/executor/nodeGather.c | modified | +3 −1 |
| src/backend/executor/nodeGatherMerge.c | modified | +3 −1 |
| src/backend/executor/nodeLimit.c | modified | +16 −82 |
| src/include/executor/execParallel.h | modified | +1 −1 |
| src/include/executor/executor.h | modified | +1 −0 |
| src/include/nodes/execnodes.h | modified | +2 −0 |
| src/test/regress/expected/select_parallel.out | modified | +23 −1 |
| src/test/regress/sql/select_parallel.sql | modified | +8 −1 |
Discussion
- [PATCH] Push limit to sort through a subquery 50 messages · 2017-04-19 → 2017-08-25