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MDEV-19834 Selectivity of an equality condition discounted twice

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When discounting selectivity of ref access, don't discount the
selectivity we've already discounted for range access.

The 10.1 version of the fix. Will need to adjust condition filtering
test results in 10.4
This commit is contained in:
Sergei Petrunia
2019-08-15 12:57:21 +03:00
parent 588e67956a
commit 1c75ad6eed
3 changed files with 67 additions and 6 deletions
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34
mysql-test/r/selectivity.result
View File

@ -1635,3 +1635,37 @@ set @@use_stat_tables= @save_use_stat_tables;
set @@optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
drop table t1;
drop function f1;
#
# MDEV-19834 Selectivity of an equality condition discounted twice
#
set @@optimizer_use_condition_selectivity=4;
set @@use_stat_tables='preferably';
create table t1 (a int, b int, key (b), key (a));
insert into t1
select (rand(1)*1000)/10, (rand(1001)*1000)/50 from seq_1_to_1000;
analyze table t1 ;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status Table is already up to date
# Check what info the optimizer has about selectivities
explain extended select * from t1 use index () where a in (17,51,5);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 1000 2.97 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` USE INDEX () where (`test`.`t1`.`a` in (17,51,5))
explain extended select * from t1 use index () where b=2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 1000 4.76 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` USE INDEX () where (`test`.`t1`.`b` = 2)
# Now, the equality is used for ref access, while the range condition
# gives selectivity data
explain extended select * from t1 where a in (17,51,5) and b=2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ref b,a b 5 const 58 2.90 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where ((`test`.`t1`.`b` = 2) and (`test`.`t1`.`a` in (17,51,5)))
drop table t1;
set use_stat_tables= @save_use_stat_tables;
set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
# End of 10.1 tests

24
mysql-test/t/selectivity.test
View File

@ -1,4 +1,5 @@
--source include/have_stat_tables.inc
--source include/have_sequence.inc
--disable_warnings
drop table if exists t0,t1,t2,t3;
@ -1102,3 +1103,26 @@ set @@optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectiv
drop table t1;
drop function f1;
--echo #
--echo # MDEV-19834 Selectivity of an equality condition discounted twice
--echo #
set @@optimizer_use_condition_selectivity=4;
set @@use_stat_tables='preferably';
create table t1 (a int, b int, key (b), key (a));
insert into t1
select (rand(1)*1000)/10, (rand(1001)*1000)/50 from seq_1_to_1000;
analyze table t1 ;
--echo # Check what info the optimizer has about selectivities
explain extended select * from t1 use index () where a in (17,51,5);
explain extended select * from t1 use index () where b=2;
--echo # Now, the equality is used for ref access, while the range condition
--echo # gives selectivity data
explain extended select * from t1 where a in (17,51,5) and b=2;
drop table t1;
set use_stat_tables= @save_use_stat_tables;
set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
--echo # End of 10.1 tests

15
sql/sql_select.cc
View File

@ -7618,6 +7618,7 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
KEYUSE *keyuse= pos->key;
KEYUSE *prev_ref_keyuse= keyuse;
uint key= keyuse->key;
bool used_range_selectivity= false;
/*
Check if we have a prefix of key=const that matches a quick select.
@ -7643,6 +7644,7 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
keyparts++;
}
sel /= (double)table->quick_rows[key] / (double) table->stat_records();
used_range_selectivity= true;
}
}
@ -7678,13 +7680,14 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
if (keyparts > keyuse->keypart)
{
/* Ok this is the keyuse that will be used for ref access */
uint fldno;
if (is_hash_join_key_no(key))
fldno= keyuse->keypart;
else
fldno= table->key_info[key].key_part[keyparts-1].fieldnr - 1;
if (keyuse->val->const_item())
if (!used_range_selectivity && keyuse->val->const_item())
{
uint fldno;
if (is_hash_join_key_no(key))
fldno= keyuse->keypart;
else
fldno= table->key_info[key].key_part[keyparts-1].fieldnr - 1;
if (table->field[fldno]->cond_selectivity > 0)
{
sel /= table->field[fldno]->cond_selectivity;