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Commit 33c66eb7 authored by unknown's avatar unknown
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MDEV-4120: UNIQUE indexes should not be considered for loose index scan 

  
Currently the loose scan code in opt_range.cc considers all indexes as
possible for the access method. Due to inexact statistics it may happen
that a loose scan is selected over a unique index.
  
This is clearly wrong since a "loose scan" over a unique index will read
the same keys as a direct index scan, but the loose scan has more overhead.
  
This task adds a rule to skip unique indexes for loose scan.
parent 3c751460
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Showing with 59 additions and 18 deletions
mysql-test/r/distinct.result
View file @ 33c66eb7
......@@ -756,7 +756,7 @@ INSERT INTO t1(a, b, c) VALUES (1, 1, 1),
(1, 2, 3);
EXPLAIN SELECT DISTINCT a, b, d, c FROM t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL PRIMARY 16 NULL 7 Using index for group-by; Using temporary
1 SIMPLE t1 range NULL a 16 NULL 7 Using index for group-by
SELECT DISTINCT a, b, d, c FROM t1;
a b d c
1 1 0 1
......
mysql-test/r/group_by.result
View file @ 33c66eb7
......@@ -2080,7 +2080,7 @@ f1 f2
explain
select col1 f1, col1 f2 from t1 group by f2 order by f2, f1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL idx 5 NULL 7 Using index for group-by; Using temporary; Using filesort
1 SIMPLE t1 index NULL idx 5 NULL 20 Using index; Using temporary; Using filesort
select col1 f1, col1 f2 from t1 group by f2 order by f2, f1;
f1 f2
1 1
......
mysql-test/r/group_min_max.result
View file @ 33c66eb7
......@@ -2126,6 +2126,31 @@ id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 index idx_t1_0,idx_t1_1,idx_t1_2 idx_t1_2 147 NULL 128 75.00 Using where; Using index
Warnings:
Note 1003 select sum(ord(`test`.`t1`.`a1`)) AS `sum(ord(a1))` from `test`.`t1` where (`test`.`t1`.`a1` > 'a') group by `test`.`t1`.`a1`,`test`.`t1`.`a2`,`test`.`t1`.`b`
create table t4 as select distinct a1, a2, b, c from t1;
alter table t4 add unique index idxt4 (a1, a2, b, c);
explain
select a1, a2, b, min(c) from t4 group by a1, a2, b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t4 index NULL idxt4 163 NULL 64 Using index
select a1, a2, b, min(c) from t4 group by a1, a2, b;
a1 a2 b min(c)
a a a a111
a a b e112
a b a i121
a b b m122
b a a a211
b a b e212
b b a i221
b b b m222
c a a a311
c a b e312
c b a i321
c b b m322
d a a a411
d a b e412
d b a i421
d b b m422
drop table t4;
explain select distinct(a1) from t1 where ord(a2) = 98;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL idx_t1_2 147 NULL 128 Using where; Using index
......@@ -2249,14 +2274,14 @@ COUNT(DISTINCT a)
1
DROP TABLE t1;
DROP PROCEDURE a;
CREATE TABLE t1 (a varchar(64) NOT NULL default '', PRIMARY KEY(a));
CREATE TABLE t1 (a varchar(64) NOT NULL default '', KEY(a));
INSERT INTO t1 (a) VALUES
(''), ('CENTRAL'), ('EASTERN'), ('GREATER LONDON'),
('NORTH CENTRAL'), ('NORTH EAST'), ('NORTH WEST'), ('SCOTLAND'),
('SOUTH EAST'), ('SOUTH WEST'), ('WESTERN');
EXPLAIN SELECT DISTINCT a,a FROM t1 ORDER BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL PRIMARY 66 NULL 12 Using index for group-by
1 SIMPLE t1 range NULL a 66 NULL 6 Using index for group-by
SELECT DISTINCT a,a FROM t1 ORDER BY a;
a a
......@@ -2314,11 +2339,11 @@ t1;
id2 id3 id5 id4 id3 id6 id5 id1
1 1 1 1 1 1 1 1
DROP TABLE t1,t2,t3,t4,t5,t6;
CREATE TABLE t1 (a int, b int, PRIMARY KEY (a,b), KEY b (b));
CREATE TABLE t1 (a int, b int, KEY (a,b), KEY b (b));
INSERT INTO t1 VALUES (1,1),(1,2),(1,0),(1,3);
explain SELECT MAX(b), a FROM t1 WHERE b < 2 AND a = 1 GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range PRIMARY,b PRIMARY 8 NULL 1 Using where; Using index for group-by
1 SIMPLE t1 range a,b a 10 NULL 1 Using where; Using index for group-by
SELECT MAX(b), a FROM t1 WHERE b < 2 AND a = 1 GROUP BY a;
MAX(b) a
1 1
......@@ -2329,7 +2354,7 @@ CREATE TABLE t2 (a int, b int, c int, PRIMARY KEY (a,b,c));
INSERT INTO t2 SELECT a,b,b FROM t1;
explain SELECT MIN(c) FROM t2 WHERE b = 2 and a = 1 and c > 1 GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 range PRIMARY PRIMARY 12 NULL 1 Using where; Using index for group-by
1 SIMPLE t2 ref PRIMARY PRIMARY 8 const,const 1 Using where; Using index
SELECT MIN(c) FROM t2 WHERE b = 2 and a = 1 and c > 1 GROUP BY a;
MIN(c)
2
......@@ -2525,7 +2550,7 @@ a MIN(b) MAX(b) AVG(b)
2 1 3 2.0000
1 1 3 2.0000
DROP TABLE t1;
create table t1 (a int, b int, primary key (a,b), key `index` (a,b)) engine=MyISAM;
create table t1 (a int, b int, key (a,b), key `index` (a,b)) engine=MyISAM;
insert into t1 (a,b) values
(0,0),(0,1),(0,2),(0,3),(0,4),(0,5),(0,6),
(0,7),(0,8),(0,9),(0,10),(0,11),(0,12),(0,13),
......@@ -2597,7 +2622,7 @@ a b
3 13
explain extended select sql_buffer_result a, max(b)+1 from t1 where a = 0 group by a;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ref PRIMARY,index PRIMARY 4 const 15 100.00 Using index; Using temporary
1 SIMPLE t1 ref a,index a 5 const 15 100.00 Using index; Using temporary
Warnings:
Note 1003 select sql_buffer_result `test`.`t1`.`a` AS `a`,(max(`test`.`t1`.`b`) + 1) AS `max(b)+1` from `test`.`t1` where (`test`.`t1`.`a` = 0) group by `test`.`t1`.`a`
drop table t1;
......@@ -3547,7 +3572,7 @@ DROP TABLE t1,t2;
CREATE TABLE t1 (
f1 int(11) NOT NULL DEFAULT '0',
f2 char(1) NOT NULL DEFAULT '',
PRIMARY KEY (f1,f2)
KEY (f1,f2)
) ;
insert into t1 values(1,'A'),(1 , 'B'), (1, 'C'), (2, 'A'),
(3, 'A'), (3, 'B'), (3, 'C'), (3, 'D');
......@@ -3558,7 +3583,7 @@ f1 COUNT(DISTINCT f2)
3 4
explain SELECT f1, COUNT(DISTINCT f2) FROM t1 GROUP BY f1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL PRIMARY 5 NULL 9 Using index for group-by (scanning)
1 SIMPLE t1 range NULL f1 5 NULL 9 Using index for group-by (scanning)
drop table t1;
# End of test#50539.
#
......@@ -3582,7 +3607,7 @@ INSERT INTO faulty (b, c) VALUES
EXPLAIN
SELECT DISTINCT b, c FROM faulty WHERE b='1802' ORDER BY c;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE faulty range b_and_c b_and_c 12 NULL 2 Using where; Using index for group-by; Using filesort
1 SIMPLE faulty ref b_and_c b_and_c 4 const 2 Using where; Using index
SELECT DISTINCT b, c FROM faulty WHERE b='1802' ORDER BY c;
b c
1802 2013-02-28 09:00:00
......
mysql-test/t/group_min_max.test
View file @ 33c66eb7
......@@ -697,6 +697,18 @@ explain select a1,a2,count(a2) from t1 group by a1,a2,b;
explain extended select a1,a2,count(a2) from t1 where (a1 > 'a') group by a1,a2,b;
explain extended select sum(ord(a1)) from t1 where (a1 > 'a') group by a1,a2,b;
#
# MDEV-4120 UNIQUE indexes should not be considered for loose index scan
#
create table t4 as select distinct a1, a2, b, c from t1;
alter table t4 add unique index idxt4 (a1, a2, b, c);
explain
select a1, a2, b, min(c) from t4 group by a1, a2, b;
select a1, a2, b, min(c) from t4 group by a1, a2, b;
drop table t4;
#
# Bug #16710: select distinct doesn't return all it should
......@@ -816,7 +828,7 @@ DROP PROCEDURE a;
# Bug #18068: SELECT DISTINCT
#
CREATE TABLE t1 (a varchar(64) NOT NULL default '', PRIMARY KEY(a));
CREATE TABLE t1 (a varchar(64) NOT NULL default '', KEY(a));
INSERT INTO t1 (a) VALUES
(''), ('CENTRAL'), ('EASTERN'), ('GREATER LONDON'),
......@@ -879,7 +891,7 @@ DROP TABLE t1,t2,t3,t4,t5,t6;
#
# Bug#22342: No results returned for query using max and group by
#
CREATE TABLE t1 (a int, b int, PRIMARY KEY (a,b), KEY b (b));
CREATE TABLE t1 (a int, b int, KEY (a,b), KEY b (b));
INSERT INTO t1 VALUES (1,1),(1,2),(1,0),(1,3);
explain SELECT MAX(b), a FROM t1 WHERE b < 2 AND a = 1 GROUP BY a;
......@@ -1003,7 +1015,7 @@ DROP TABLE t1;
# Bug#38195: Incorrect handling of aggregate functions when loose index scan is
# used causes server crash.
#
create table t1 (a int, b int, primary key (a,b), key `index` (a,b)) engine=MyISAM;
create table t1 (a int, b int, key (a,b), key `index` (a,b)) engine=MyISAM;
insert into t1 (a,b) values
(0,0),(0,1),(0,2),(0,3),(0,4),(0,5),(0,6),
(0,7),(0,8),(0,9),(0,10),(0,11),(0,12),(0,13),
......@@ -1390,7 +1402,7 @@ DROP TABLE t1,t2;
CREATE TABLE t1 (
f1 int(11) NOT NULL DEFAULT '0',
f2 char(1) NOT NULL DEFAULT '',
PRIMARY KEY (f1,f2)
KEY (f1,f2)
) ;
insert into t1 values(1,'A'),(1 , 'B'), (1, 'C'), (2, 'A'),
(3, 'A'), (3, 'B'), (3, 'C'), (3, 'D');
......
sql/opt_range.cc
View file @ 33c66eb7
......@@ -12411,8 +12411,12 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree, double read_time)
uchar cur_key_infix[MAX_KEY_LENGTH];
uint cur_used_key_parts;
/* Check (B1) - if current index is covering. */
if (!table->covering_keys.is_set(cur_index))
/*
Check (B1) - if current index is covering. Exclude UNIQUE indexes, because
loose scan may still be chosen for them due to imperfect cost calculations.
*/
if (!table->covering_keys.is_set(cur_index) ||
cur_index_info->flags & HA_NOSAME)
goto next_index;
/*
......
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