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If we expect a hash join to be performed in multiple batches, suppress

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"physical tlist" optimization on the outer relation (ie, force a projection
step to occur in its scan).  This avoids storing useless column values when
the outer relation's tuples are written to temporary batch files.

Modified version of a patch by Michael Henderson and Ramon Lawrence.
This commit is contained in:
Tom Lane
2009-03-26 17:15:35 +00:00
parent ee4c187f64
commit f38fbf31f5
5 changed files with 25 additions and 6 deletions
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15
src/backend/optimizer/util/pathnode.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.150 2009/02/27 00:06:27 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.151 2009/03/26 17:15:35 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1480,9 +1480,20 @@ create_hashjoin_path(PlannerInfo *root,
pathnode->jpath.outerjoinpath = outer_path;
pathnode->jpath.innerjoinpath = inner_path;
pathnode->jpath.joinrestrictinfo = restrict_clauses;
/* A hashjoin never has pathkeys, since its ordering is unpredictable */
/*
* A hashjoin never has pathkeys, since its output ordering is
* unpredictable due to possible batching. XXX If the inner relation is
* small enough, we could instruct the executor that it must not batch,
* and then we could assume that the output inherits the outer relation's
* ordering, which might save a sort step. However there is considerable
* downside if our estimate of the inner relation size is badly off.
* For the moment we don't risk it. (Note also that if we wanted to take
* this seriously, joinpath.c would have to consider many more paths for
* the outer rel than it does now.)
*/
pathnode->jpath.path.pathkeys = NIL;
pathnode->path_hashclauses = hashclauses;
/* cost_hashjoin will fill in pathnode->num_batches */
cost_hashjoin(pathnode, root, sjinfo);