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Recognize self-contradictory restriction clauses for non-table relations.

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The constraint exclusion feature checks for contradictions among scan
restriction clauses, as well as contradictions between those clauses and a
table's CHECK constraints.  The first aspect of this testing can be useful
for non-table relations (such as subqueries or functions-in-FROM), but the
feature was coded with only the CHECK case in mind so we were applying it
only to plain-table RTEs.  Move the relation_excluded_by_constraints call
so that it is applied to all RTEs not just plain tables.  With the default
setting of constraint_exclusion this results in no extra work, but with
constraint_exclusion = ON we will detect optimizations that we missed
before (at the cost of more planner cycles than we expended before).

Per a gripe from Gunnlaugur Þór Briem.  Experimentation with
his example also showed we were not being very bright about the case where
constraint exclusion is proven within a subquery within UNION ALL, so tweak
the code to allow set_append_rel_pathlist to recognize such cases.
This commit is contained in:
Tom Lane
2011-09-24 19:33:16 -04:00
parent 337c0b0361
commit 7741dd6590
3 changed files with 45 additions and 22 deletions
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7
src/backend/optimizer/plan/planner.c
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@ -60,7 +60,6 @@ static Node *preprocess_expression(PlannerInfo *root, Node *expr, int kind);
static void preprocess_qual_conditions(PlannerInfo *root, Node *jtnode);
static Plan *inheritance_planner(PlannerInfo *root);
static Plan *grouping_planner(PlannerInfo *root, double tuple_fraction);
static bool is_dummy_plan(Plan *plan);
static void preprocess_rowmarks(PlannerInfo *root);
static double preprocess_limit(PlannerInfo *root,
double tuple_fraction,
@ -1841,9 +1840,11 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
* is deemed not to need scanning due to constraint exclusion.
*
* Currently, such dummy plans are Result nodes with constant FALSE
* filter quals.
* filter quals (see set_dummy_rel_pathlist and create_append_plan).
*
* XXX this probably ought to be somewhere else, but not clear where.
*/
static bool
bool
is_dummy_plan(Plan *plan)
{
if (IsA(plan, Result))