From a87c729153e372f3731689a7be007bc2b53f1410 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 28 Mar 2014 11:50:01 -0400
Subject: [PATCH] Fix EquivalenceClass processing for nested append relations.
The original coding of EquivalenceClasses didn't foresee that appendrel
child relations might themselves be appendrels; but this is possible for
example when a UNION ALL subquery scans a table with inheritance children.
The oversight led to failure to optimize ordering-related issues very well
for the grandchild tables. After some false starts involving explicitly
flattening the appendrel representation, we found that this could be fixed
easily by removing a few implicit assumptions about appendrel parent rels
not being children themselves.
Kyotaro Horiguchi and Tom Lane, reviewed by Noah Misch
---
src/backend/optimizer/path/allpaths.c | 20 ++++++++---
src/backend/optimizer/path/equivclass.c | 12 ++++---
src/backend/optimizer/plan/createplan.c | 2 +-
src/test/regress/expected/union.out | 47 +++++++++++++++++++++++++
src/test/regress/sql/union.sql | 29 +++++++++++++++
5 files changed, 101 insertions(+), 9 deletions(-)
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 03be7b1fe88..5777cb2ff0c 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -1021,10 +1021,15 @@ get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
* accumulate_append_subpath
* Add a subpath to the list being built for an Append or MergeAppend
*
- * It's possible that the child is itself an Append path, in which case
- * we can "cut out the middleman" and just add its child paths to our
- * own list. (We don't try to do this earlier because we need to
- * apply both levels of transformation to the quals.)
+ * It's possible that the child is itself an Append or MergeAppend path, in
+ * which case we can "cut out the middleman" and just add its child paths to
+ * our own list. (We don't try to do this earlier because we need to apply
+ * both levels of transformation to the quals.)
+ *
+ * Note that if we omit a child MergeAppend in this way, we are effectively
+ * omitting a sort step, which seems fine: if the parent is to be an Append,
+ * its result would be unsorted anyway, while if the parent is to be a
+ * MergeAppend, there's no point in a separate sort on a child.
*/
static List *
accumulate_append_subpath(List *subpaths, Path *path)
@@ -1036,6 +1041,13 @@ accumulate_append_subpath(List *subpaths, Path *path)
/* list_copy is important here to avoid sharing list substructure */
return list_concat(subpaths, list_copy(apath->subpaths));
}
+ else if (IsA(path, MergeAppendPath))
+ {
+ MergeAppendPath *mpath = (MergeAppendPath *) path;
+
+ /* list_copy is important here to avoid sharing list substructure */
+ return list_concat(subpaths, list_copy(mpath->subpaths));
+ }
else
return lappend(subpaths, path);
}
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 35d2a83599d..ac12f84fd5e 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -1937,16 +1937,20 @@ add_child_rel_equivalences(PlannerInfo *root,
if (cur_ec->ec_has_volatile)
continue;
- /* No point in searching if parent rel not mentioned in eclass */
- if (!bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
+ /*
+ * No point in searching if parent rel not mentioned in eclass; but
+ * we can't tell that for sure if parent rel is itself a child.
+ */
+ if (parent_rel->reloptkind == RELOPT_BASEREL &&
+ !bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
continue;
foreach(lc2, cur_ec->ec_members)
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
- if (cur_em->em_is_const || cur_em->em_is_child)
- continue; /* ignore consts and children here */
+ if (cur_em->em_is_const)
+ continue; /* ignore consts here */
/* Does it reference parent_rel? */
if (bms_overlap(cur_em->em_relids, parent_rel->relids))
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 184d37a8818..784805fbf43 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -751,7 +751,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path)
/* Compute sort column info, and adjust MergeAppend's tlist as needed */
(void) prepare_sort_from_pathkeys(root, plan, pathkeys,
- NULL,
+ best_path->path.parent->relids,
NULL,
true,
&node->numCols,
diff --git a/src/test/regress/expected/union.out b/src/test/regress/expected/union.out
index 6f9ee5eb471..6a7d0f2a889 100644
--- a/src/test/regress/expected/union.out
+++ b/src/test/regress/expected/union.out
@@ -502,9 +502,56 @@ explain (costs off)
Index Cond: (ab = 'ab'::text)
(7 rows)
+--
+-- Test that ORDER BY for UNION ALL can be pushed down to inheritance
+-- children.
+--
+CREATE TEMP TABLE t1c (b text, a text);
+ALTER TABLE t1c INHERIT t1;
+CREATE TEMP TABLE t2c (primary key (ab)) INHERITS (t2);
+INSERT INTO t1c VALUES ('v', 'w'), ('c', 'd'), ('m', 'n'), ('e', 'f');
+INSERT INTO t2c VALUES ('vw'), ('cd'), ('mn'), ('ef');
+CREATE INDEX t1c_ab_idx on t1c ((a || b));
+set enable_seqscan = on;
+set enable_indexonlyscan = off;
+explain (costs off)
+ SELECT * FROM
+ (SELECT a || b AS ab FROM t1
+ UNION ALL
+ SELECT ab FROM t2) t
+ ORDER BY 1 LIMIT 8;
+ QUERY PLAN
+------------------------------------------------
+ Limit
+ -> Merge Append
+ Sort Key: ((t1.a || t1.b))
+ -> Index Scan using t1_ab_idx on t1
+ -> Index Scan using t1c_ab_idx on t1c
+ -> Index Scan using t2_pkey on t2
+ -> Index Scan using t2c_pkey on t2c
+(7 rows)
+
+ SELECT * FROM
+ (SELECT a || b AS ab FROM t1
+ UNION ALL
+ SELECT ab FROM t2) t
+ ORDER BY 1 LIMIT 8;
+ ab
+----
+ ab
+ ab
+ cd
+ dc
+ ef
+ fe
+ mn
+ nm
+(8 rows)
+
reset enable_seqscan;
reset enable_indexscan;
reset enable_bitmapscan;
+reset enable_indexonlyscan;
-- Test constraint exclusion of UNION ALL subqueries
explain (costs off)
SELECT * FROM
diff --git a/src/test/regress/sql/union.sql b/src/test/regress/sql/union.sql
index d567cf14819..5205435e2fd 100644
--- a/src/test/regress/sql/union.sql
+++ b/src/test/regress/sql/union.sql
@@ -198,9 +198,38 @@ explain (costs off)
SELECT * FROM t2) t
WHERE ab = 'ab';
+--
+-- Test that ORDER BY for UNION ALL can be pushed down to inheritance
+-- children.
+--
+
+CREATE TEMP TABLE t1c (b text, a text);
+ALTER TABLE t1c INHERIT t1;
+CREATE TEMP TABLE t2c (primary key (ab)) INHERITS (t2);
+INSERT INTO t1c VALUES ('v', 'w'), ('c', 'd'), ('m', 'n'), ('e', 'f');
+INSERT INTO t2c VALUES ('vw'), ('cd'), ('mn'), ('ef');
+CREATE INDEX t1c_ab_idx on t1c ((a || b));
+
+set enable_seqscan = on;
+set enable_indexonlyscan = off;
+
+explain (costs off)
+ SELECT * FROM
+ (SELECT a || b AS ab FROM t1
+ UNION ALL
+ SELECT ab FROM t2) t
+ ORDER BY 1 LIMIT 8;
+
+ SELECT * FROM
+ (SELECT a || b AS ab FROM t1
+ UNION ALL
+ SELECT ab FROM t2) t
+ ORDER BY 1 LIMIT 8;
+
reset enable_seqscan;
reset enable_indexscan;
reset enable_bitmapscan;
+reset enable_indexonlyscan;
-- Test constraint exclusion of UNION ALL subqueries
explain (costs off)
--
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