Hi Varun, As far as I understand, the intent of the patch is that this check: + for (uint i=0; i < n; i++) + { + if (item1->element_index(i)->cmp_type() != + item2->element_index(i)->cmp_type()) matches this check in subquery_types_allow_materialization() if (!inner->type_handler()->subquery_type_allows_materialization(inner, outer)) which has implementations like so: bool Type_handler_real_result:: subquery_type_allows_materialization(const Item *inner, const Item *outer) const { DBUG_ASSERT(inner->cmp_type() == REAL_RESULT); return outer->cmp_type() == REAL_RESULT; } // .. and the same for other datatypes ... I would like to see comments in both places (cmp_row_types and subquery_types_allow_materialization()) explaining that. Note that some Type_handler::subquery_types_allow_materialization() have a more complex implementation, for example Type_handler_string_result::subquery_types_allow_materialization() compares collations. Is there any reasons why cmp_row_types() doesn't use the same call as subquery_types_allow_materialization does: if (!inner->type_handler()->subquery_type_allows_materialization(inner, outer)) ? On Mon, Nov 04, 2019 at 04:38:02PM +0530, Varun wrote:
revision-id: 3a11b49bb5b716538f98c6a212bbbfa6fc9b7a88 (mariadb-10.3.17-145-g3a11b49bb5b) parent(s): 162f475c4be81dfbceed093ad03d114b4c69a3c0 author: Varun Gupta committer: Varun Gupta timestamp: 2019-11-04 16:28:25 +0530 message:
MDEV-20900: IN predicate to IN subquery conversion causes performance regression
Disable the IN predicate to IN subquery conversion when the types on the left and right hand side of the IN predicate are not of comparable type.
--- mysql-test/main/opt_tvc.result | 53 ++++++++++++++++++++++++++++++++++++++---- mysql-test/main/opt_tvc.test | 31 ++++++++++++++++++++++++ sql/sql_tvc.cc | 27 ++++++++++++++++++++- 3 files changed, 106 insertions(+), 5 deletions(-)
diff --git a/mysql-test/main/opt_tvc.result b/mysql-test/main/opt_tvc.result index 5329a9f64be..a68e70e8a25 100644 --- a/mysql-test/main/opt_tvc.result +++ b/mysql-test/main/opt_tvc.result @@ -629,11 +629,9 @@ SELECT * FROM t1 WHERE i IN (NULL, NULL, NULL, NULL, NULL); i EXPLAIN EXTENDED SELECT * FROM t1 WHERE i IN (NULL, NULL, NULL, NULL, NULL); id select_type table type possible_keys key key_len ref rows filtered Extra -1 PRIMARY t1 ALL NULL NULL NULL NULL 3 100.00 -1 PRIMARY <derived3> ALL NULL NULL NULL NULL 5 100.00 Using where; FirstMatch(t1); Using join buffer (flat, BNL join) -3 DERIVED NULL NULL NULL NULL NULL NULL NULL NULL No tables used +1 SIMPLE t1 ALL NULL NULL NULL NULL 3 100.00 Using where Warnings: -Note 1003 /* select#1 */ select `test`.`t1`.`i` AS `i` from `test`.`t1` semi join ((values (NULL),(NULL),(NULL),(NULL),(NULL)) `tvc_0`) where `test`.`t1`.`i` = `tvc_0`.`_col_1` +Note 1003 select `test`.`t1`.`i` AS `i` from `test`.`t1` where `test`.`t1`.`i` in (NULL,NULL,NULL,NULL,NULL) SET in_predicate_conversion_threshold= default; DROP TABLE t1; # @@ -687,3 +685,50 @@ f1 f2 1 1 DROP TABLE t1,t2,t3; SET @@in_predicate_conversion_threshold= default; +# +# MDEV-20900: IN predicate to IN subquery conversion causes performance regression +# +create table t1(a int, b int); +insert into t1 select seq-1, seq-1 from seq_1_to_10; +set in_predicate_conversion_threshold=2; +explain select * from t1 where t1.a IN ("1","2","3","4"); +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 10 Using where +select * from t1 where t1.a IN ("1","2","3","4"); +a b +1 1 +2 2 +3 3 +4 4 +set in_predicate_conversion_threshold=0; +explain select * from t1 where t1.a IN ("1","2","3","4"); +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 10 Using where +select * from t1 where t1.a IN ("1","2","3","4"); +a b +1 1 +2 2 +3 3 +4 4 +set in_predicate_conversion_threshold=2; +explain select * from t1 where (t1.a,t1.b) in (("1","1"),(2,2),(3,3),(4,4)); +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 10 Using where +select * from t1 where (t1.a,t1.b) in (("1","1"),(2,2),(3,3),(4,4)); +a b +1 1 +2 2 +3 3 +4 4 +set in_predicate_conversion_threshold=0; +explain select * from t1 where (t1.a,t1.b) in (("1","1"),(2,2),(3,3),(4,4)); +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 10 Using where +select * from t1 where (t1.a,t1.b) in (("1","1"),(2,2),(3,3),(4,4)); +a b +1 1 +2 2 +3 3 +4 4 +drop table t1; +SET @@in_predicate_conversion_threshold= default; diff --git a/mysql-test/main/opt_tvc.test b/mysql-test/main/opt_tvc.test index 7319dbdc9e8..e4e8c6d7919 100644 --- a/mysql-test/main/opt_tvc.test +++ b/mysql-test/main/opt_tvc.test @@ -3,6 +3,7 @@ # source include/have_debug.inc; source include/default_optimizer_switch.inc; +source include/have_sequence.inc;
create table t1 (a int, b int);
@@ -397,3 +398,33 @@ SELECT * FROM t3 WHERE (f1,f2) IN ((2, 2), (1, 2), (3, 5), (1, 1)); DROP TABLE t1,t2,t3;
SET @@in_predicate_conversion_threshold= default; + +--echo # +--echo # MDEV-20900: IN predicate to IN subquery conversion causes performance regression +--echo # + +create table t1(a int, b int); +insert into t1 select seq-1, seq-1 from seq_1_to_10; + +set in_predicate_conversion_threshold=2; + +let $query= select * from t1 where t1.a IN ("1","2","3","4"); +eval explain $query; +eval $query; + +set in_predicate_conversion_threshold=0; +eval explain $query; +eval $query; + +set in_predicate_conversion_threshold=2; +let $query= select * from t1 where (t1.a,t1.b) in (("1","1"),(2,2),(3,3),(4,4)); +eval explain $query; +eval $query; + +set in_predicate_conversion_threshold=0; +eval explain $query; +eval $query; + +drop table t1; +SET @@in_predicate_conversion_threshold= default; + diff --git a/sql/sql_tvc.cc b/sql/sql_tvc.cc index 816c6fe1089..78c7c34a81a 100644 --- a/sql/sql_tvc.cc +++ b/sql/sql_tvc.cc @@ -796,6 +796,31 @@ bool Item_subselect::wrap_tvc_into_select(THD *thd, st_select_lex *tvc_sl) }
+/* + @brief + Check whether the items are of comparable type or not + + @retval + 0 comparable + 1 not comparable +*/ + +static bool cmp_row_types(Item* item1, Item* item2) +{ + uint n= item1->cols(); + if (item2->check_cols(n)) + return true; + + for (uint i=0; i < n; i++) + { + if (item1->element_index(i)->cmp_type() != + item2->element_index(i)->cmp_type()) + return true; + } + return false; +} + + /** @brief Transform IN predicate into IN subquery @@ -843,7 +868,7 @@ Item *Item_func_in::in_predicate_to_in_subs_transformer(THD *thd,
for (uint i=1; i < arg_count; i++) { - if (!args[i]->const_item()) + if (!args[i]->const_item() || cmp_row_types(args[0], args[i])) return this; }
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