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; _______________________________________________ commits mailing list commits@mariadb.org https://lists.askmonty.org/cgi-bin/mailman/listinfo/commits

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