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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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32
mysql-test/main/range_vs_index_merge.result
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@ -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