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Improve create_unique_path to not be fooled by unrelated clauses that happen

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to be syntactically part of a semijoin clause.  For example given
WHERE EXISTS(SELECT ... WHERE upper.var = lower.var AND some-condition)
where some-condition is just a restriction on the lower relation, we can
use unique-ification on lower.var after having applied some-condition within
the scan on lower.
This commit is contained in:
Tom Lane 2009-02-27 00:06:27 +00:00
parent f4fea44ce1
commit f01313bc0d
1 changed files with 60 additions and 8 deletions
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68
src/backend/optimizer/util/pathnode.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.149 2009/01/01 17:23:44 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.150 2009/02/27 00:06:27 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -765,12 +765,26 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
*/
oldcontext = MemoryContextSwitchTo(root->planner_cxt);
/*
/*----------
* Look to see whether the semijoin's join quals consist of AND'ed
* equality operators, with (only) RHS variables on only one side of
* each one. If so, we can figure out how to enforce uniqueness for
* the RHS.
*
* Note that the input join_quals list is the list of quals that are
* *syntactically* associated with the semijoin, which in practice means
* the synthesized comparison list for an IN or the WHERE of an EXISTS.
* Particularly in the latter case, it might contain clauses that aren't
* *semantically* associated with the join, but refer to just one side or
* the other. We can ignore such clauses here, as they will just drop
* down to be processed within one side or the other. (It is okay to
* consider only the syntactically-associated clauses here because for a
* semijoin, no higher-level quals could refer to the RHS, and so there
* can be no other quals that are semantically associated with this join.
* We do things this way because it is useful to be able to run this test
* before we have extracted the list of quals that are actually
* semantically associated with the particular join.)
*
* Note that the in_operators list consists of the joinqual operators
* themselves (but commuted if needed to put the RHS value on the right).
* These could be cross-type operators, in which case the operator
@ -778,6 +792,7 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
* We assume here that that operator will be available from the btree
* or hash opclass when the time comes ... if not, create_unique_plan()
* will fail.
*----------
*/
in_operators = NIL;
uniq_exprs = NIL;
@ -791,19 +806,52 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
Node *right_expr;
Relids left_varnos;
Relids right_varnos;
Relids all_varnos;
/* must be binary opclause... */
if (!IsA(op, OpExpr))
goto no_unique_path;
if (list_length(op->args) != 2)
/* Is it a binary opclause? */
if (!IsA(op, OpExpr) ||
list_length(op->args) != 2)
{
/* No, but does it reference both sides? */
all_varnos = pull_varnos((Node *) op);
if (!bms_overlap(all_varnos, sjinfo->syn_righthand) ||
bms_is_subset(all_varnos, sjinfo->syn_righthand))
{
/*
* Clause refers to only one rel, so ignore it --- unless it
* contains volatile functions, in which case we'd better
* punt.
*/
if (contain_volatile_functions((Node *) op))
goto no_unique_path;
continue;
}
/* Non-operator clause referencing both sides, must punt */
goto no_unique_path;
}
/* Extract data from binary opclause */
opno = op->opno;
left_expr = linitial(op->args);
right_expr = lsecond(op->args);
/* check rel membership of arguments */
left_varnos = pull_varnos(left_expr);
right_varnos = pull_varnos(right_expr);
all_varnos = bms_union(left_varnos, right_varnos);
/* Does it reference both sides? */
if (!bms_overlap(all_varnos, sjinfo->syn_righthand) ||
bms_is_subset(all_varnos, sjinfo->syn_righthand))
{
/*
* Clause refers to only one rel, so ignore it --- unless it
* contains volatile functions, in which case we'd better punt.
*/
if (contain_volatile_functions((Node *) op))
goto no_unique_path;
continue;
}
/* check rel membership of arguments */
if (!bms_is_empty(right_varnos) &&
bms_is_subset(right_varnos, sjinfo->syn_righthand) &&
!bms_overlap(left_varnos, sjinfo->syn_righthand))
@ -845,6 +893,10 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
uniq_exprs = lappend(uniq_exprs, copyObject(right_expr));
}
/* Punt if we didn't find at least one column to unique-ify */
if (uniq_exprs == NIL)
goto no_unique_path;
/*
* The expressions we'd need to unique-ify mustn't be volatile.
*/