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Teach the planner to treat a partial unique index as proving a variable is

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unique for a particular query, if the index predicate is satisfied.  This
requires a bit of reordering of operations so that we check the predicates
before doing any selectivity estimates, but shouldn't really cause any
noticeable slowdown.  Per a comment from Michal Politowski.
This commit is contained in:
Tom Lane
2009-02-15 20:16:21 +00:00
parent 57b5984d24
commit ce6e31de9c
5 changed files with 70 additions and 39 deletions
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63
src/backend/utils/adt/selfuncs.c
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@ -15,7 +15,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.258 2009/01/01 17:23:50 momjian Exp $
* $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.259 2009/02/15 20:16:21 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -234,6 +234,15 @@ var_eq_const(VariableStatData *vardata, Oid operator,
if (constisnull)
return 0.0;
/*
* If we matched the var to a unique index, assume there is exactly one
* match regardless of anything else. (This is slightly bogus, since
* the index's equality operator might be different from ours, but it's
* more likely to be right than ignoring the information.)
*/
if (vardata->isunique && vardata->rel && vardata->rel->tuples >= 1.0)
return 1.0 / vardata->rel->tuples;
if (HeapTupleIsValid(vardata->statsTuple))
{
Form_pg_statistic stats;
@ -357,6 +366,15 @@ var_eq_non_const(VariableStatData *vardata, Oid operator,
{
double selec;
/*
* If we matched the var to a unique index, assume there is exactly one
* match regardless of anything else. (This is slightly bogus, since
* the index's equality operator might be different from ours, but it's
* more likely to be right than ignoring the information.)
*/
if (vardata->isunique && vardata->rel && vardata->rel->tuples >= 1.0)
return 1.0 / vardata->rel->tuples;
if (HeapTupleIsValid(vardata->statsTuple))
{
Form_pg_statistic stats;
@ -3969,6 +3987,8 @@ get_join_variables(PlannerInfo *root, List *args, SpecialJoinInfo *sjinfo,
* atttype, atttypmod: type data to pass to get_attstatsslot(). This is
* commonly the same as the exposed type of the variable argument,
* but can be different in binary-compatible-type cases.
* isunique: TRUE if we were able to match the var to a unique index,
* implying its values are unique for this query.
*
* Caller is responsible for doing ReleaseVariableStats() before exiting.
*/
@ -4005,6 +4025,7 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
vardata->rel = find_base_rel(root, var->varno);
vardata->atttype = var->vartype;
vardata->atttypmod = var->vartypmod;
vardata->isunique = has_unique_index(vardata->rel, var->varattno);
rte = root->simple_rte_array[var->varno];
@ -4121,13 +4142,6 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
if (indexpr_item == NULL)
continue; /* no expressions here... */
/*
* Ignore partial indexes since they probably don't reflect
* whole-relation statistics. Possibly reconsider this later.
*/
if (index->indpred)
continue;
for (pos = 0; pos < index->ncolumns; pos++)
{
if (index->indexkeys[pos] == 0)
@ -4147,9 +4161,19 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
*/
if (index->unique &&
index->ncolumns == 1 &&
index->indpred == NIL)
(index->indpred == NIL || index->predOK))
vardata->isunique = true;
/* Has it got stats? */
/*
* Has it got stats? We only consider stats for
* non-partial indexes, since partial indexes
* probably don't reflect whole-relation statistics;
* the above check for uniqueness is the only info
* we take from a partial index.
*
* An index stats hook, however, must make its own
* decisions about what to do with partial indexes.
*/
if (get_index_stats_hook &&
(*get_index_stats_hook) (root, index->indexoid,
pos + 1, vardata))
@ -4163,7 +4187,7 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
!vardata->freefunc)
elog(ERROR, "no function provided to release variable stats with");
}
else
else if (index->indpred == NIL)
{
vardata->statsTuple =
SearchSysCache(STATRELATT,
@ -4254,19 +4278,12 @@ get_variable_numdistinct(VariableStatData *vardata)
/*
* If there is a unique index for the variable, assume it is unique no
* matter what pg_statistic says (the statistics could be out of date).
* Can skip search if we already think it's unique.
* matter what pg_statistic says; the statistics could be out of date,
* or we might have found a partial unique index that proves the var
* is unique for this query.
*/
if (stadistinct != -1.0)
{
if (vardata->isunique)
stadistinct = -1.0;
else if (vardata->var && IsA(vardata->var, Var) &&
vardata->rel &&
has_unique_index(vardata->rel,
((Var *) vardata->var)->varattno))
stadistinct = -1.0;
}
if (vardata->isunique)
stadistinct = -1.0;
/*
* If we had an absolute estimate, use that.