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Use MinimalTuple for tuple queues.

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This representation saves 8 bytes per tuple compared to HeapTuple, and
avoids the need to allocate, copy and free on the receiving side.

Gather can emit the returned MinimalTuple directly, but GatherMerge now
needs to make an explicit copy because it buffers multiple tuples at a
time.  That should be no worse than before.

Reviewed-by: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKG%2B8T_ggoUTAE-U%3DA%2BOcPc4%3DB0nPPHcSfffuQhvXXjML6w%40mail.gmail.com
This commit is contained in:
Thomas Munro
2020-07-17 14:57:50 +12:00
parent d2bddc2500
commit cdc7169509
5 changed files with 51 additions and 47 deletions
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8
src/backend/optimizer/plan/createplan.c
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@ -1730,8 +1730,10 @@ create_gather_plan(PlannerInfo *root, GatherPath *best_path)
List *tlist;
/*
* Although the Gather node can project, we prefer to push down such work
* to its child node, so demand an exact tlist from the child.
* Push projection down to the child node. That way, the projection work
* is parallelized, and there can be no system columns in the result (they
* can't travel through a tuple queue because it uses MinimalTuple
* representation).
*/
subplan = create_plan_recurse(root, best_path->subpath, CP_EXACT_TLIST);
@ -1766,7 +1768,7 @@ create_gather_merge_plan(PlannerInfo *root, GatherMergePath *best_path)
List *pathkeys = best_path->path.pathkeys;
List *tlist = build_path_tlist(root, &best_path->path);
/* As with Gather, it's best to project away columns in the workers. */
/* As with Gather, project away columns in the workers. */
subplan = create_plan_recurse(root, best_path->subpath, CP_EXACT_TLIST);
/* Create a shell for a GatherMerge plan. */