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Teach tuplestore.c to throw away data before the "mark" point when the caller

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is using mark/restore but not rewind or backward-scan capability.  Insert a
materialize plan node between a mergejoin and its inner child if the inner
child is a sort that is expected to spill to disk.  The materialize shields
the sort from the need to do mark/restore and thereby allows it to perform
its final merge pass on-the-fly; while the materialize itself is normally
cheap since it won't spill to disk unless the number of tuples with equal
key values exceeds work_mem.

Greg Stark, with some kibitzing from Tom Lane.
This commit is contained in:
Tom Lane
2007-05-21 17:57:35 +00:00
parent 3963574d13
commit 2415ad9831
8 changed files with 236 additions and 40 deletions
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26
src/backend/optimizer/plan/createplan.c
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@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.230 2007/05/04 01:13:44 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.231 2007/05/21 17:57:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1600,6 +1600,30 @@ create_mergejoin_plan(PlannerInfo *root,
else
innerpathkeys = best_path->jpath.innerjoinpath->pathkeys;
/*
* If inner plan is a sort that is expected to spill to disk, add a
* materialize node to shield it from the need to handle mark/restore.
* This will allow it to perform the last merge pass on-the-fly, while
* in most cases not requiring the materialize to spill to disk.
*
* XXX really, Sort oughta do this for itself, probably, to avoid the
* overhead of a separate plan node.
*/
if (IsA(inner_plan, Sort) &&
sort_exceeds_work_mem((Sort *) inner_plan))
{
Plan *matplan = (Plan *) make_material(inner_plan);
/*
* We assume the materialize will not spill to disk, and therefore
* charge just cpu_tuple_cost per tuple.
*/
copy_plan_costsize(matplan, inner_plan);
matplan->total_cost += cpu_tuple_cost * matplan->plan_rows;
inner_plan = matplan;
}
/*
* Compute the opfamily/strategy/nullsfirst arrays needed by the executor.
* The information is in the pathkeys for the two inputs, but we need to