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MDEV-17761: Odd optimizer choice with ORDER BY LIMIT and condition selectivity

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Make the "ORDER BY ... LIMIT n" optimizer take into account condition
selectivity data from EITS (not just from potential range accesses).
This commit is contained in:
Sergei Petrunia
2019-01-23 15:49:49 +03:00
parent 36a2a185fe
commit b7a784ae25
5 changed files with 145 additions and 0 deletions
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37
mysql-test/main/order_by.result
View File

@ -3253,3 +3253,40 @@ Warnings:
Note 1003 select `test`.`wings`.`id` AS `wing_id`,`test`.`wings`.`department_id` AS `department_id` from `test`.`wings` semi join (`test`.`books`) where `test`.`books`.`library_id` = 8663 and `test`.`books`.`scheduled_for_removal` = 0 and `test`.`wings`.`id` = `test`.`books`.`wings_id` order by `test`.`wings`.`id`
set optimizer_switch= @save_optimizer_switch;
DROP TABLE books, wings;
#
# MDEV-17761: Odd optimizer choice with ORDER BY LIMIT and condition selectivity
#
create table t1(a int);
insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t2(a int);
insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
create table t3(a int);
insert into t3 select A.a + 1000 *B.a from t2 A, t1 B;
create table t4 (
a int,
b int,
c int,
filler1 char(255),
filler2 char(255),
key(a)
);
insert into t4 select a,a,a, a,a from t3;
set @tmp_h=@@histogram_size, @tmp_u=@@use_stat_tables,
@tmp_o=@@optimizer_use_condition_selectivity;
set histogram_size=100;
set use_stat_tables=preferably;
set optimizer_use_condition_selectivity=4;
analyze table t4 persistent for columns(b) indexes ();
Table Op Msg_type Msg_text
test.t4 analyze status Engine-independent statistics collected
test.t4 analyze status Table is already up to date
# rows must be around 1200, not 600:
explain extended
select * from t4 where b < 5000 order by a limit 600;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t4 index NULL a 5 NULL 1188 100.00 Using where
Warnings:
Note 1003 select `test`.`t4`.`a` AS `a`,`test`.`t4`.`b` AS `b`,`test`.`t4`.`c` AS `c`,`test`.`t4`.`filler1` AS `filler1`,`test`.`t4`.`filler2` AS `filler2` from `test`.`t4` where `test`.`t4`.`b` < 5000 order by `test`.`t4`.`a` limit 600
set histogram_size=@tmp_h, use_stat_tables=@tmp_u,
optimizer_use_condition_selectivity=@tmp_o;
drop table t1,t2,t3,t4;

37
mysql-test/main/order_by.test
View File

@ -2187,3 +2187,40 @@ eval explain extended $q;
set optimizer_switch= @save_optimizer_switch;
DROP TABLE books, wings;
--echo #
--echo # MDEV-17761: Odd optimizer choice with ORDER BY LIMIT and condition selectivity
--echo #
create table t1(a int);
insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t2(a int);
insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
create table t3(a int);
insert into t3 select A.a + 1000 *B.a from t2 A, t1 B;
create table t4 (
a int,
b int,
c int,
filler1 char(255),
filler2 char(255),
key(a)
);
insert into t4 select a,a,a, a,a from t3;
set @tmp_h=@@histogram_size, @tmp_u=@@use_stat_tables,
@tmp_o=@@optimizer_use_condition_selectivity;
set histogram_size=100;
set use_stat_tables=preferably;
set optimizer_use_condition_selectivity=4;
analyze table t4 persistent for columns(b) indexes ();
--echo # rows must be around 1200, not 600:
explain extended
select * from t4 where b < 5000 order by a limit 600;
set histogram_size=@tmp_h, use_stat_tables=@tmp_u,
optimizer_use_condition_selectivity=@tmp_o;
drop table t1,t2,t3,t4;

32
mysql-test/main/range_vs_index_merge.result
View File

@ -1320,6 +1320,37 @@ WHERE ((Name > 'Ca' AND Name < 'Cf') OR (Country > 'E' AND Country < 'H'))
AND (Population >= 100000 AND Population < 120000)
ORDER BY Population LIMIT 5;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE City index_merge Country,Name,Population Name,Country 35,3 NULL # Using sort_union(Name,Country); Using where; Using filesort
FLUSH STATUS;
SELECT * FROM City
WHERE ((Name > 'Ca' AND Name < 'Cf') OR (Country > 'E' AND Country < 'H'))
AND (Population >= 100000 AND Population < 120000)
ORDER BY Population LIMIT 5;
ID Name Country Population
519 Worthing GBR 100000
638 al-Arish EGY 100447
518 Basildon GBR 100924
707 Marbella ESP 101144
3792 Tartu EST 101246
SHOW STATUS LIKE 'Handler_read_%';
Variable_name Value
Handler_read_first 0
Handler_read_key 2
Handler_read_last 0
Handler_read_next 385
Handler_read_prev 0
Handler_read_retry 0
Handler_read_rnd 377
Handler_read_rnd_deleted 0
Handler_read_rnd_next 0
set @tmp_mdev585=@@optimizer_use_condition_selectivity;
set optimizer_use_condition_selectivity=1;
EXPLAIN
SELECT * FROM City
WHERE ((Name > 'Ca' AND Name < 'Cf') OR (Country > 'E' AND Country < 'H'))
AND (Population >= 100000 AND Population < 120000)
ORDER BY Population LIMIT 5;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE City range Country,Name,Population Population 4 NULL # Using where
FLUSH STATUS;
SELECT * FROM City
@ -1343,6 +1374,7 @@ Handler_read_retry 0
Handler_read_rnd 0
Handler_read_rnd_deleted 0
Handler_read_rnd_next 0
set optimizer_use_condition_selectivity=@tmp_mdev585;
set optimizer_switch='index_merge=off';
EXPLAIN
SELECT * FROM City

17
mysql-test/main/range_vs_index_merge.test
View File

@ -718,6 +718,23 @@ SELECT * FROM City
ORDER BY Population LIMIT 5;
SHOW STATUS LIKE 'Handler_read_%';
set @tmp_mdev585=@@optimizer_use_condition_selectivity;
set optimizer_use_condition_selectivity=1;
--replace_column 9 #
EXPLAIN
SELECT * FROM City
WHERE ((Name > 'Ca' AND Name < 'Cf') OR (Country > 'E' AND Country < 'H'))
AND (Population >= 100000 AND Population < 120000)
ORDER BY Population LIMIT 5;
FLUSH STATUS;
SELECT * FROM City
WHERE ((Name > 'Ca' AND Name < 'Cf') OR (Country > 'E' AND Country < 'H'))
AND (Population >= 100000 AND Population < 120000)
ORDER BY Population LIMIT 5;
SHOW STATUS LIKE 'Handler_read_%';
set optimizer_use_condition_selectivity=@tmp_mdev585;
set optimizer_switch='index_merge=off';

22
sql/sql_select.cc
View File

@ -26884,7 +26884,11 @@ test_if_cheaper_ordering(const JOIN_TAB *tab, ORDER *order, TABLE *table,
uint tablenr= (uint)(tab - join->join_tab);
read_time= join->best_positions[tablenr].read_time;
for (uint i= tablenr+1; i < join->table_count; i++)
{
fanout*= join->best_positions[i].records_read; // fanout is always >= 1
// But selectivity is =< 1 :
fanout*= join->best_positions[i].cond_selectivity;
}
}
else
read_time= table->file->scan_time();
@ -27022,6 +27026,23 @@ test_if_cheaper_ordering(const JOIN_TAB *tab, ORDER *order, TABLE *table,
*/
select_limit= (ha_rows) (select_limit < fanout ?
1 : select_limit/fanout);
/*
refkey_rows_estimate is E(#rows) produced by the table access
strategy that was picked without regard to ORDER BY ... LIMIT.
It will be used as the source of selectivity data.
Use table->cond_selectivity as a better estimate which includes
condition selectivity too.
*/
{
// we use MIN(...), because "Using LooseScan" queries have
// cond_selectivity=1 while refkey_rows_estimate has a better
// estimate.
refkey_rows_estimate= MY_MIN(refkey_rows_estimate,
table_records * table->cond_selectivity);
}
/*
We assume that each of the tested indexes is not correlated
with ref_key. Thus, to select first N records we have to scan
@ -27032,6 +27053,7 @@ test_if_cheaper_ordering(const JOIN_TAB *tab, ORDER *order, TABLE *table,
N/(refkey_rows_estimate/table_records) > table_records
<=> N > refkey_rows_estimate.
*/
if (select_limit > refkey_rows_estimate)
select_limit= table_records;
else