[Commits] 3032cd8e91f: step #1: if a derived table has SELECT DISTINCT, provide index statistics for it so that the join optimizer in the

Sergey Petrunia sergey at mariadb.com
Fri Apr 26 19:17:00 EEST 2019


Hi Varun,

Please mention the MDEV# in the commit comment.

Otherwise, the patch is ok to push.

On Mon, Apr 22, 2019 at 07:09:45PM +0530, Varun wrote:
> revision-id: 3032cd8e91f1e1ead8b6f941e75cd29e473e7eaa (mariadb-10.3.10-283-g3032cd8e91f)
> parent(s): f4019f5b3544a18f3ddf32df2c5214c3f8dabdce
> author: Varun Gupta
> committer: Varun Gupta
> timestamp: 2019-04-22 18:19:25 +0530
> message:
> 
> step #1: 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.
> 
> ---
>  mysql-test/main/cte_nonrecursive.result            |  8 ++--
>  mysql-test/main/derived.result                     | 54 ++++++++++++++++++++++
>  mysql-test/main/derived.test                       | 30 ++++++++++++
>  mysql-test/main/derived_view.result                |  2 +-
>  mysql-test/main/subselect_extra.result             |  2 +-
>  mysql-test/main/subselect_extra_no_semijoin.result |  2 +-
>  sql/sql_lex.h                                      |  1 +
>  sql/sql_union.cc                                   | 40 ++++++++++++++++
>  sql/table.cc                                       | 20 ++++++++
>  9 files changed, 152 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	
> diff --git a/sql/sql_lex.h b/sql/sql_lex.h
> index 72ca4ac0b43..4eaec7d062b 100644
> --- a/sql/sql_lex.h
> +++ b/sql/sql_lex.h
> @@ -896,6 +896,7 @@ class st_select_lex_unit: public st_select_lex_node {
>    bool union_needs_tmp_table();
>  
>    void set_unique_exclude();
> +  bool check_distinct_in_union();
>  
>    friend struct LEX;
>    friend int subselect_union_engine::exec();
> diff --git a/sql/sql_union.cc b/sql/sql_union.cc
> index 87fbbebe4ba..3fb5552c77a 100644
> --- a/sql/sql_union.cc
> +++ b/sql/sql_union.cc
> @@ -2049,3 +2049,43 @@ void st_select_lex_unit::set_unique_exclude()
>      }
>    }
>  }
> +
> +/**
> +  @brief
> +  Check if the derived table is guaranteed to have distinct rows because of
> +  UNION operations used to populate it.
> +
> +  @detail
> +    UNION operation removes duplicate rows from its output. That is, a query like
> +
> +      select * from t1 UNION select * from t2
> +
> +    will not produce duplicate rows in its output, even if table t1 (and/or t2)
> +    contain duplicate rows. EXCEPT and INTERSECT operations also have this
> +    property.
> +
> +    On the other hand, UNION ALL operation doesn't remove duplicates. (The SQL
> +    standard also defines EXCEPT ALL and INTERSECT ALL, but we don't support
> +    them).
> +
> +    st_select_lex_unit computes its value left to right. That is, if there is
> +     a st_select_lex_unit object describing
> +
> +      (select #1) OP1 (select #2) OP2 (select #3)
> +
> +    then ((select #1) OP1 (select #2)) is computed first, and OP2 is computed
> +    second.
> +
> +    How can one tell if st_select_lex_unit is guaranteed to have distinct
> +    output rows? This depends on whether the last operation was duplicate-
> +    removing or not:
> +    - UNION ALL is not duplicate-removing
> +    - all other operations are duplicate-removing
> +*/
> +
> +bool st_select_lex_unit::check_distinct_in_union()
> +{
> +  if (union_distinct && !union_distinct->next_select())
> +    return true;
> +  return false;
> +}
> diff --git a/sql/table.cc b/sql/table.cc
> index 80995abc1f9..c4494c9ae4b 100644
> --- a/sql/table.cc
> +++ b/sql/table.cc
> @@ -7269,6 +7269,26 @@ bool TABLE::add_tmp_key(uint key, uint key_parts,
>      key_part_info++;
>    }
>  
> +  /*
> +    For the case when there is a derived table that would give distinct rows,
> +    the index statistics are passed to the join optimizer to tell that a ref
> +    access to all the fields of the derived table will produce only one row.
> +  */
> +
> +  st_select_lex_unit* derived= pos_in_table_list ?
> +                               pos_in_table_list->derived: NULL;
> +  if (derived)
> +  {
> +    st_select_lex* first= derived->first_select();
> +    uint select_list_items= first->get_item_list()->elements;
> +    if (key_parts == select_list_items)
> +    {
> +      if ((!first->is_part_of_union() && (first->options & SELECT_DISTINCT)) ||
> +          derived->check_distinct_in_union())
> +        keyinfo->rec_per_key[key_parts - 1]= 1;
> +    }
> +  }
> +
>    set_if_bigger(s->max_key_length, keyinfo->key_length);
>    s->keys++;
>    return FALSE;
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-- 
BR
 Sergei
-- 
Sergei Petrunia, Software Developer
MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog




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