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Improve cost estimation for aggregates and window functions.

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The previous coding failed to account properly for the costs of evaluating
the input expressions of aggregates and window functions, as seen in a
recent gripe from Claudio Freire.  (I said at the time that it wasn't
counting these costs at all; but on closer inspection, it was effectively
charging these costs once per output tuple.  That is completely wrong for
aggregates, and not exactly right for window functions either.)

There was also a hard-wired assumption that aggregates and window functions
had procost 1.0, which is now fixed to respect the actual cataloged costs.

The costing of WindowAgg is still pretty bogus, since it doesn't try to
estimate the effects of spilling data to disk, but that seems like a
separate issue.
This commit is contained in:
Tom Lane
2011-04-24 16:55:20 -04:00
parent f6322b3191
commit e6a30a8c3c
11 changed files with 198 additions and 106 deletions
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4
src/include/optimizer/cost.h
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@@ -94,12 +94,12 @@ extern void cost_material(Path *path,
Cost input_startup_cost, Cost input_total_cost,
double tuples, int width);
extern void cost_agg(Path *path, PlannerInfo *root,
AggStrategy aggstrategy, int numAggs,
AggStrategy aggstrategy, const AggClauseCosts *aggcosts,
int numGroupCols, double numGroups,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples);
extern void cost_windowagg(Path *path, PlannerInfo *root,
int numWindowFuncs, int numPartCols, int numOrderCols,
List *windowFuncs, int numPartCols, int numOrderCols,
Cost input_startup_cost, Cost input_total_cost,
double input_tuples);
extern void cost_group(Path *path, PlannerInfo *root,