From 3104a928663d5dc3ff159cb59636845131f1da08 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 2 Mar 2005 04:10:53 +0000
Subject: [PATCH] Another go at making pred_test() handle all reasonable
combinations of AND and OR clauses. The key point here is that an OR on the
predicate side has to be treated gingerly: we may be able to prove that the
OR is implied even when no one of its components is implied. For example (x
OR y) implies (x OR y OR z) even though no one of x, y, or z can be
individually proven. This code handles both the example shown recently by
Sergey Koshcheyev and the one shown last October by Dawid Kuroczko.
---
src/backend/optimizer/path/indxpath.c | 275 +++++++++++++++-----------
1 file changed, 158 insertions(+), 117 deletions(-)
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index ec28bf0408d..f86206304c1 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.168 2005/03/01 00:24:52 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.169 2005/03/02 04:10:53 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -64,9 +64,7 @@ static bool match_join_clause_to_indexcol(RelOptInfo *rel, IndexOptInfo *index,
RestrictInfo *rinfo);
static Oid indexable_operator(Expr *clause, Oid opclass,
bool indexkey_on_left);
-static bool pred_test_restrict_list(Expr *predicate, List *restrictinfo_list);
-static bool pred_test_recurse_restrict(Expr *predicate, Node *clause);
-static bool pred_test_recurse_pred(Expr *predicate, Node *clause);
+static bool pred_test_recurse(Node *clause, Node *predicate);
static bool pred_test_simple_clause(Expr *predicate, Node *clause);
static Relids indexable_outerrelids(RelOptInfo *rel, IndexOptInfo *index);
static Path *make_innerjoin_index_path(Query *root,
@@ -749,30 +747,17 @@ check_partial_indexes(Query *root, RelOptInfo *rel)
* Recursively checks whether the clauses in restrictinfo_list imply
* that the given predicate is true.
*
- * This routine (together with the routines it calls) iterates over
- * ANDs in the predicate first, then breaks down the restriction list
- * to its constituent AND/OR elements, and iterates over ORs
- * in the predicate last. This order is important to make the test
- * succeed whenever possible. --Nels, Jan '93
- *
- * For example, a restriction (a OR b) certainly implies a predicate
- * (a OR b OR c), but no one element of the predicate is individually
- * implied by the restriction. By expanding the predicate ORs last
- * we are able to prove that the whole predicate is implied by each arm
- * of the restriction. Conversely consider predicate (a AND b) with
- * restriction (a AND b AND c). This should be implied but we will
- * fail to prove it if we dissect the restriction first.
- *
* The top-level List structure of each list corresponds to an AND list.
- * We assume that canonicalize_qual() has been applied and so there
- * are no explicit ANDs immediately below the top-level List structure.
- * (If this is not true we might fail to prove an implication that is
- * valid, but no worse consequences will ensue.)
+ * We assume that canonicalize_qual() has been applied and so there are
+ * no un-flattened ANDs or ORs (e.g., no AND immediately within an AND,
+ * including AND just below the top-level List structure).
+ * If this is not true we might fail to prove an implication that is
+ * valid, but no worse consequences will ensue.
*/
bool
pred_test(List *predicate_list, List *restrictinfo_list)
{
- ListCell *pred;
+ ListCell *item;
/*
* Note: if Postgres tried to optimize queries by forming equivalence
@@ -793,133 +778,189 @@ pred_test(List *predicate_list, List *restrictinfo_list)
return false; /* no restriction clauses: the test must
* fail */
- /* Take care of the AND semantics of the top-level predicate list */
- foreach(pred, predicate_list)
+ /*
+ * In all cases where the predicate is an AND-clause, pred_test_recurse()
+ * will prefer to iterate over the predicate's components. So we can
+ * just do that to start with here, and eliminate the need for
+ * pred_test_recurse() to handle a bare List on the predicate side.
+ *
+ * Logic is: restriction must imply each of the AND'ed predicate items.
+ */
+ foreach(item, predicate_list)
{
- /*
- * if any clause is not implied, the whole predicate is not
- * implied.
- */
- if (!pred_test_restrict_list(lfirst(pred), restrictinfo_list))
+ if (!pred_test_recurse((Node *) restrictinfo_list, lfirst(item)))
return false;
}
return true;
}
-/*
- * pred_test_restrict_list
- * Does the "predicate inclusion test" for one AND clause of a predicate
- * expression. Here we take care of the AND semantics of the top-level
- * restrictinfo list.
- */
-static bool
-pred_test_restrict_list(Expr *predicate, List *restrictinfo_list)
-{
- ListCell *item;
-
- foreach(item, restrictinfo_list)
- {
- /* if any clause implies the predicate, return true */
- if (pred_test_recurse_restrict(predicate,
- (Node *) lfirst(item)))
- return true;
- }
- return false;
-}
-
-
-/*
- * pred_test_recurse_restrict
- * Does the "predicate inclusion test" for one AND clause of a predicate
- * expression. Here we recursively deal with the possibility that the
- * restriction-list element is itself an AND or OR structure; also,
- * we strip off RestrictInfo nodes to find bare qualifier expressions.
+/*----------
+ * pred_test_recurse
+ * Does the "predicate inclusion test" for non-NULL restriction and
+ * predicate clauses.
+ *
+ * The logic followed here is ("=>" means "implies"):
+ * atom A => atom B iff: pred_test_simple_clause says so
+ * atom A => AND-expr B iff: A => each of B's components
+ * atom A => OR-expr B iff: A => any of B's components
+ * AND-expr A => atom B iff: any of A's components => B
+ * AND-expr A => AND-expr B iff: A => each of B's components
+ * AND-expr A => OR-expr B iff: A => any of B's components,
+ * *or* any of A's components => B
+ * OR-expr A => atom B iff: each of A's components => B
+ * OR-expr A => AND-expr B iff: A => each of B's components
+ * OR-expr A => OR-expr B iff: each of A's components => any of B's
+ *
+ * An "atom" is anything other than an AND or OR node. Notice that we don't
+ * have any special logic to handle NOT nodes; these should have been pushed
+ * down or eliminated where feasible by prepqual.c.
+ *
+ * We can't recursively expand either side first, but have to interleave
+ * the expansions per the above rules, to be sure we handle all of these
+ * examples:
+ * (x OR y) => (x OR y OR z)
+ * (x AND y AND z) => (x AND y)
+ * (x AND y) => ((x AND y) OR z)
+ * ((x OR y) AND z) => (x OR y)
+ * This is still not an exhaustive test, but it handles most normal cases
+ * under the assumption that both inputs have been AND/OR flattened.
+ *
+ * A bare List node on the restriction side is interpreted as an AND clause,
+ * in order to handle the top-level restriction List properly. However we
+ * need not consider a List on the predicate side since pred_test() already
+ * expanded it.
+ *
+ * We have to be prepared to handle RestrictInfo nodes in the restrictinfo
+ * tree, though not in the predicate tree.
+ *----------
*/
static bool
-pred_test_recurse_restrict(Expr *predicate, Node *clause)
+pred_test_recurse(Node *clause, Node *predicate)
{
- List *items;
ListCell *item;
Assert(clause != NULL);
+ /* skip through RestrictInfo */
if (IsA(clause, RestrictInfo))
{
- RestrictInfo *restrictinfo = (RestrictInfo *) clause;
-
- return pred_test_recurse_restrict(predicate,
- (Node *) restrictinfo->clause);
+ clause = (Node *) ((RestrictInfo *) clause)->clause;
+ Assert(clause != NULL);
+ Assert(!IsA(clause, RestrictInfo));
}
- else if (or_clause(clause))
+ Assert(predicate != NULL);
+
+ /*
+ * Since a restriction List clause is handled the same as an AND clause,
+ * we can avoid duplicate code like this:
+ */
+ if (and_clause(clause))
+ clause = (Node *) ((BoolExpr *) clause)->args;
+
+ if (IsA(clause, List))
{
- items = ((BoolExpr *) clause)->args;
- foreach(item, items)
+ if (and_clause(predicate))
{
- /* if any OR item doesn't imply the predicate, clause doesn't */
- if (!pred_test_recurse_restrict(predicate, lfirst(item)))
- return false;
+ /* AND-clause => AND-clause if A implies each of B's items */
+ foreach(item, ((BoolExpr *) predicate)->args)
+ {
+ if (!pred_test_recurse(clause, lfirst(item)))
+ return false;
+ }
+ return true;
+ }
+ else if (or_clause(predicate))
+ {
+ /* AND-clause => OR-clause if A implies any of B's items */
+ /* Needed to handle (x AND y) => ((x AND y) OR z) */
+ foreach(item, ((BoolExpr *) predicate)->args)
+ {
+ if (pred_test_recurse(clause, lfirst(item)))
+ return true;
+ }
+ /* Also check if any of A's items implies B */
+ /* Needed to handle ((x OR y) AND z) => (x OR y) */
+ foreach(item, (List *) clause)
+ {
+ if (pred_test_recurse(lfirst(item), predicate))
+ return true;
+ }
+ return false;
+ }
+ else
+ {
+ /* AND-clause => atom if any of A's items implies B */
+ foreach(item, (List *) clause)
+ {
+ if (pred_test_recurse(lfirst(item), predicate))
+ return true;
+ }
+ return false;
}
- return true;
}
- else if (and_clause(clause))
+ else if (or_clause(clause))
{
- items = ((BoolExpr *) clause)->args;
- foreach(item, items)
+ if (or_clause(predicate))
{
/*
- * if any AND item implies the predicate, the whole clause
- * does
+ * OR-clause => OR-clause if each of A's items implies any of
+ * B's items. Messy but can't do it any more simply.
*/
- if (pred_test_recurse_restrict(predicate, lfirst(item)))
- return true;
+ foreach(item, ((BoolExpr *) clause)->args)
+ {
+ Node *citem = lfirst(item);
+ ListCell *item2;
+
+ foreach(item2, ((BoolExpr *) predicate)->args)
+ {
+ if (pred_test_recurse(citem, lfirst(item2)))
+ break;
+ }
+ if (item2 == NULL)
+ return false; /* doesn't imply any of B's */
+ }
+ return true;
+ }
+ else
+ {
+ /* OR-clause => AND-clause if each of A's items implies B */
+ /* OR-clause => atom if each of A's items implies B */
+ foreach(item, ((BoolExpr *) clause)->args)
+ {
+ if (!pred_test_recurse(lfirst(item), predicate))
+ return false;
+ }
+ return true;
}
- return false;
}
else
- return pred_test_recurse_pred(predicate, clause);
-}
-
-
-/*
- * pred_test_recurse_pred
- * Does the "predicate inclusion test" for one conjunct of a predicate
- * expression. Here we recursively deal with the possibility that the
- * predicate conjunct is itself an AND or OR structure.
- */
-static bool
-pred_test_recurse_pred(Expr *predicate, Node *clause)
-{
- List *items;
- ListCell *item;
-
- Assert(predicate != NULL);
- if (or_clause((Node *) predicate))
{
- items = ((BoolExpr *) predicate)->args;
- foreach(item, items)
+ if (and_clause(predicate))
{
- /* if any item is implied, the whole predicate is implied */
- if (pred_test_recurse_pred(lfirst(item), clause))
- return true;
+ /* atom => AND-clause if A implies each of B's items */
+ foreach(item, ((BoolExpr *) predicate)->args)
+ {
+ if (!pred_test_recurse(clause, lfirst(item)))
+ return false;
+ }
+ return true;
}
- return false;
- }
- else if (and_clause((Node *) predicate))
- {
- items = ((BoolExpr *) predicate)->args;
- foreach(item, items)
+ else if (or_clause(predicate))
{
- /*
- * if any item is not implied, the whole predicate is not
- * implied
- */
- if (!pred_test_recurse_pred(lfirst(item), clause))
- return false;
+ /* atom => OR-clause if A implies any of B's items */
+ foreach(item, ((BoolExpr *) predicate)->args)
+ {
+ if (pred_test_recurse(clause, lfirst(item)))
+ return true;
+ }
+ return false;
+ }
+ else
+ {
+ /* atom => atom is the base case */
+ return pred_test_simple_clause((Expr *) predicate, clause);
}
- return true;
}
- else
- return pred_test_simple_clause(predicate, clause);
}
--
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