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Revise parameterized-path mechanism to fix assorted issues.

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This patch adjusts the treatment of parameterized paths so that all paths
with the same parameterization (same set of required outer rels) for the
same relation will have the same rowcount estimate.  We cache the rowcount
estimates to ensure that property, and hopefully save a few cycles too.
Doing this makes it practical for add_path_precheck to operate without
a rowcount estimate: it need only assume that paths with different
parameterizations never dominate each other, which is close enough to
true anyway for coarse filtering, because normally a more-parameterized
path should yield fewer rows thanks to having more join clauses to apply.

In add_path, we do the full nine yards of comparing rowcount estimates
along with everything else, so that we can discard parameterized paths that
don't actually have an advantage.  This fixes some issues I'd found with
add_path rejecting parameterized paths on the grounds that they were more
expensive than not-parameterized ones, even though they yielded many fewer
rows and hence would be cheaper once subsequent joining was considered.

To make the same-rowcounts assumption valid, we have to require that any
parameterized path enforce *all* join clauses that could be obtained from
the particular set of outer rels, even if not all of them are useful for
indexing.  This is required at both base scans and joins.  It's a good
thing anyway since the net impact is that join quals are checked at the
lowest practical level in the join tree.  Hence, discard the original
rather ad-hoc mechanism for choosing parameterization joinquals, and build
a better one that has a more principled rule for when clauses can be moved.
The original rule was actually buggy anyway for lack of knowledge about
which relations are part of an outer join's outer side; getting this right
requires adding an outer_relids field to RestrictInfo.
This commit is contained in:
Tom Lane
2012-04-19 15:52:46 -04:00
parent cd1f4db4ae
commit 5b7b5518d0
30 changed files with 1793 additions and 782 deletions
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16
src/include/optimizer/cost.h
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@@ -66,17 +66,20 @@ extern int constraint_exclusion;
extern double clamp_row_est(double nrows);
extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
double index_pages, PlannerInfo *root);
extern void cost_seqscan(Path *path, PlannerInfo *root, RelOptInfo *baserel);
extern void cost_seqscan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info);
extern void cost_index(IndexPath *path, PlannerInfo *root,
double loop_count);
extern void cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *param_info,
Path *bitmapqual, double loop_count);
extern void cost_bitmap_and_node(BitmapAndPath *path, PlannerInfo *root);
extern void cost_bitmap_or_node(BitmapOrPath *path, PlannerInfo *root);
extern void cost_bitmap_tree_node(Path *path, Cost *cost, Selectivity *selec);
extern void cost_tidscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, List *tidquals);
extern void cost_subqueryscan(Path *path, RelOptInfo *baserel);
extern void cost_subqueryscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel, ParamPathInfo *param_info);
extern void cost_functionscan(Path *path, PlannerInfo *root,
RelOptInfo *baserel);
extern void cost_valuesscan(Path *path, PlannerInfo *root,
@@ -149,6 +152,15 @@ extern void compute_semi_anti_join_factors(PlannerInfo *root,
List *restrictlist,
SemiAntiJoinFactors *semifactors);
extern void set_baserel_size_estimates(PlannerInfo *root, RelOptInfo *rel);
extern double get_parameterized_baserel_size(PlannerInfo *root,
RelOptInfo *rel,
List *param_clauses);
extern double get_parameterized_joinrel_size(PlannerInfo *root,
RelOptInfo *rel,
double outer_rows,
double inner_rows,
SpecialJoinInfo *sjinfo,
List *restrict_clauses);
extern void set_joinrel_size_estimates(PlannerInfo *root, RelOptInfo *rel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,