MDEV-9959: A serious MariaDB server performance bug

If a derived table has SELECT DISTINCT, provide index statistics for it so that the join optimizer in the
upper select knows that ref access to the table will produce one row.

6 files changed, 91 insertions, 7 deletions

diff --git a/mysql-test/main/cte_nonrecursive.result b/mysql-test/main/cte_nonrecursive.result
index b846ec2d8ac..d80d34ecc7f 100644
--- a/mysql-test/main/cte_nonrecursive.result
+++ b/mysql-test/main/cte_nonrecursive.result
@@ -244,7 +244,7 @@ with t as (select distinct a from t1 where b >= 'c')
 select * from t as r1, t as r2 where r1.a=r2.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	8	Using where
-1	PRIMARY	<derived3>	ref	key0	key0	5	r1.a	2	
+1	PRIMARY	<derived3>	ref	key0	key0	5	r1.a	1	
 3	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	8	Using where; Using temporary
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	8	Using where; Using temporary
 explain
@@ -253,7 +253,7 @@ select * from (select distinct a from t1 where b >= 'c') as r1,
 where r1.a=r2.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	8	Using where
-1	PRIMARY	<derived3>	ref	key0	key0	5	r1.a	2	
+1	PRIMARY	<derived3>	ref	key0	key0	5	r1.a	1	
 3	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	8	Using where; Using temporary
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	8	Using where; Using temporary
 # two references to t specified by a query
@@ -369,7 +369,7 @@ select c as a from t2 where c < 4)
 select * from t2,t where t2.c=t.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	4	Using where
-1	PRIMARY	<derived2>	ref	key0	key0	5	test.t2.c	2	
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t2.c	1	
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
 3	UNION	t2	ALL	NULL	NULL	NULL	NULL	4	Using where
 NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
@@ -381,7 +381,7 @@ select c as a from t2 where c < 4) as t
 where t2.c=t.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	4	Using where
-1	PRIMARY	<derived2>	ref	key0	key0	5	test.t2.c	2	
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t2.c	1	
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
 3	UNION	t2	ALL	NULL	NULL	NULL	NULL	4	Using where
 NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
diff --git a/mysql-test/main/derived.result b/mysql-test/main/derived.result
index f0d0289c1ce..857246d68b4 100644
--- a/mysql-test/main/derived.result
+++ b/mysql-test/main/derived.result
@@ -1195,3 +1195,57 @@ drop table t1,t2,t3;
 #
 # End of 10.2 tests
 #
+#
+# MDEV-9959: A serious MariaDB server performance bug
+#
+create table t1(a int);
+insert into t1 values (1),(2),(3),(4),(5),(6);
+create table t2(a int, b int,c int);
+insert into t2(a,b,c) values (1,1,2),(2,2,3),(3,1,4),(4,2,2),(5,1,1),(6,2,5);
+create table t3(a int, b int);
+insert into t3(a,b) values (1,1),(2,2),(2,1),(1,2),(5,1),(9,2);
+table "<derived2>" should have type=ref and rows=1
+one select in derived table
+with distinct
+analyze select * from t1 , ((select distinct t2.a from t2 order by c))q  where t1.a=q.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	Using where
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t1.a	1	1.00	100.00	100.00	
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	Using temporary; Using filesort
+analyze select * from t1 , ((select distinct t2.a, t2.b from t2 order by c))q  where t1.a=q.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	Using where
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t1.a	2	1.00	100.00	100.00	
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	Using temporary; Using filesort
+# multiple selects in derived table
+# NO UNION ALL
+analyze select * from t1 , ( (select t2.a from t2 order by c) union  (select t2.a from t2 order by c))q  where t1.a=q.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	Using where
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t1.a	1	1.00	100.00	100.00	
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	
+3	UNION	t2	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	6.00	NULL	NULL	
+select * from t1 , ( (select t2.a from t2 order by c) union  (select t2.a from t2 order by c))q  where t1.a=q.a;
+a	a
+1	1
+2	2
+3	3
+4	4
+5	5
+6	6
+# UNION ALL and EXCEPT
+analyze select * from t1 , ( (select t2.a from t2 order by c) union all (select  t2.a from t2 order by c) except(select t3.a from t3 order by b))q  where t1.a=q.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	Using where
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t1.a	1	0.50	100.00	100.00	
+2	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	
+3	UNION	t2	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	
+4	EXCEPT	t3	ALL	NULL	NULL	NULL	NULL	6	6.00	100.00	100.00	
+NULL	UNIT RESULT	<unit2,3,4>	ALL	NULL	NULL	NULL	NULL	NULL	3.00	NULL	NULL	
+select * from t1 , ( (select t2.a from t2 order by c) union all (select  t2.a from t2 order by c) except(select t3.a from t3 order by b))q  where t1.a=q.a;
+a	a
+3	3
+4	4
+6	6
+drop table t1,t2,t3;
diff --git a/mysql-test/main/derived.test b/mysql-test/main/derived.test
index 6c51f23c51e..990f955450a 100644
--- a/mysql-test/main/derived.test
+++ b/mysql-test/main/derived.test
@@ -1032,3 +1032,33 @@ drop table t1,t2,t3;
 --echo #
 --echo # End of 10.2 tests
 --echo #
+
+--echo #
+--echo # MDEV-9959: A serious MariaDB server performance bug
+--echo #
+
+create table t1(a int);
+insert into t1 values (1),(2),(3),(4),(5),(6);
+create table t2(a int, b int,c int);
+insert into t2(a,b,c) values (1,1,2),(2,2,3),(3,1,4),(4,2,2),(5,1,1),(6,2,5);
+create table t3(a int, b int);
+insert into t3(a,b) values (1,1),(2,2),(2,1),(1,2),(5,1),(9,2);
+
+--echo table "<derived2>" should have type=ref and rows=1
+--echo one select in derived table
+
+--echo with distinct
+analyze select * from t1 , ((select distinct t2.a from t2 order by c))q  where t1.a=q.a; 
+analyze select * from t1 , ((select distinct t2.a, t2.b from t2 order by c))q  where t1.a=q.a;
+
+--echo # multiple selects in derived table
+--echo # NO UNION ALL
+analyze select * from t1 , ( (select t2.a from t2 order by c) union  (select t2.a from t2 order by c))q  where t1.a=q.a;
+select * from t1 , ( (select t2.a from t2 order by c) union  (select t2.a from t2 order by c))q  where t1.a=q.a;
+
+--echo # UNION ALL and EXCEPT
+analyze select * from t1 , ( (select t2.a from t2 order by c) union all (select  t2.a from t2 order by c) except(select t3.a from t3 order by b))q  where t1.a=q.a;
+
+select * from t1 , ( (select t2.a from t2 order by c) union all (select  t2.a from t2 order by c) except(select t3.a from t3 order by b))q  where t1.a=q.a;
+
+drop table t1,t2,t3;
diff --git a/mysql-test/main/derived_view.result b/mysql-test/main/derived_view.result
index 86dd73f5733..30831e75341 100644
--- a/mysql-test/main/derived_view.result
+++ b/mysql-test/main/derived_view.result
@@ -1525,7 +1525,7 @@ EXPLAIN
 SELECT a FROM t1 WHERE (a,b) IN (SELECT * FROM v2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
-1	PRIMARY	<derived3>	ref	key0	key0	10	test.t1.a,test.t1.b	2	FirstMatch(t1)
+1	PRIMARY	<derived3>	ref	key0	key0	10	test.t1.a,test.t1.b	1	FirstMatch(t1)
 3	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	6	
 4	UNION	t3	ALL	NULL	NULL	NULL	NULL	4	
 NULL	UNION RESULT	<union3,4>	ALL	NULL	NULL	NULL	NULL	NULL	
diff --git a/mysql-test/main/subselect_extra.result b/mysql-test/main/subselect_extra.result
index a3a0f1f9a15..dbcf00268c2 100644
--- a/mysql-test/main/subselect_extra.result
+++ b/mysql-test/main/subselect_extra.result
@@ -409,7 +409,7 @@ EXPLAIN
 SELECT a FROM t1 WHERE (a,b) IN (SELECT * FROM v2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
-1	PRIMARY	<derived3>	ref	key0	key0	10	test.t1.a,test.t1.b	2	FirstMatch(t1)
+1	PRIMARY	<derived3>	ref	key0	key0	10	test.t1.a,test.t1.b	1	FirstMatch(t1)
 3	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	6	
 4	UNION	t3	ALL	NULL	NULL	NULL	NULL	4	
 NULL	UNION RESULT	<union3,4>	ALL	NULL	NULL	NULL	NULL	NULL	
diff --git a/mysql-test/main/subselect_extra_no_semijoin.result b/mysql-test/main/subselect_extra_no_semijoin.result
index ec9ddb0452e..49a1431eb9b 100644
--- a/mysql-test/main/subselect_extra_no_semijoin.result
+++ b/mysql-test/main/subselect_extra_no_semijoin.result
@@ -411,7 +411,7 @@ EXPLAIN
 SELECT a FROM t1 WHERE (a,b) IN (SELECT * FROM v2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
-2	DEPENDENT SUBQUERY	<derived3>	index_subquery	key0	key0	10	func,func	2	Using where
+2	DEPENDENT SUBQUERY	<derived3>	index_subquery	key0	key0	10	func,func	1	Using where
 3	DERIVED	t2	ALL	NULL	NULL	NULL	NULL	6	
 4	UNION	t3	ALL	NULL	NULL	NULL	NULL	4	
 NULL	UNION RESULT	<union3,4>	ALL	NULL	NULL	NULL	NULL	NULL