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Rewrite the planner's handling of materialized plan types so that there is

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an explicit model of rescan costs being different from first-time costs.
The costing of Material nodes in particular now has some visible relationship
to the actual runtime behavior, where before it was essentially fantasy.
This also fixes up a couple of places where different materialized plan types
were treated differently for no very good reason (probably just oversights).

A couple of the regression tests are affected, because the planner now chooses
to put the other relation on the inside of a nestloop-with-materialize.
So far as I can see both changes are sane, and the planner is now more
consistently following the expectation that it should prefer to materialize
the smaller of two relations.

Per a recent discussion with Robert Haas.
This commit is contained in:
Tom Lane
2009-09-12 22:12:09 +00:00
parent 5f1b32ddf8
commit 9bb342811b
12 changed files with 1029 additions and 916 deletions
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6
src/backend/optimizer/util/pathnode.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.152 2009/06/11 14:48:59 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.153 2009/09/12 22:12:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -711,6 +711,7 @@ create_material_path(RelOptInfo *rel, Path *subpath)
pathnode->subpath = subpath;
cost_material(&pathnode->path,
subpath->startup_cost,
subpath->total_cost,
rel->rows,
rel->width);
@ -1424,7 +1425,8 @@ create_mergejoin_path(PlannerInfo *root,
* cost_mergejoin will avoid choosing anyway). Therefore
* cost_material's cost estimate is bogus and we should charge just
* cpu_tuple_cost per tuple. (Keep this estimate in sync with similar
* ones in cost_mergejoin and create_mergejoin_plan.)
* ones in cost_mergejoin and create_mergejoin_plan; also see
* cost_rescan.)
*/
mpath->startup_cost = inner_path->startup_cost;
mpath->total_cost = inner_path->total_cost;