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MDEV-4120: UNIQUE indexes should not be considered for loose index scan

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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.
This commit is contained in:
unknown
2013-08-21 10:51:08 +03:00
parent 3c75146052
commit 33c66eb7fb
5 changed files with 59 additions and 18 deletions
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2
mysql-test/r/distinct.result
View File

@ -756,7 +756,7 @@ INSERT INTO t1(a, b, c) VALUES (1, 1, 1),
(1, 2, 3); (1, 2, 3);
EXPLAIN SELECT DISTINCT a, b, d, c FROM t1; EXPLAIN SELECT DISTINCT a, b, d, c FROM t1;
id select_type table type possible_keys key key_len ref rows Extra 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; SELECT DISTINCT a, b, d, c FROM t1;
a b d c a b d c
1 1 0 1 1 1 0 1

2
mysql-test/r/group_by.result
View File

@ -2080,7 +2080,7 @@ f1 f2
explain explain
select col1 f1, col1 f2 from t1 group by f2 order by f2, f1; 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 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; select col1 f1, col1 f2 from t1 group by f2 order by f2, f1;
f1 f2 f1 f2
1 1 1 1

45
mysql-test/r/group_min_max.result
View File

@ -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 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: 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` 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; explain select distinct(a1) from t1 where ord(a2) = 98;
id select_type table type possible_keys key key_len ref rows Extra 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 1 SIMPLE t1 index NULL idx_t1_2 147 NULL 128 Using where; Using index
@ -2249,14 +2274,14 @@ COUNT(DISTINCT a)
1 1
DROP TABLE t1; DROP TABLE t1;
DROP PROCEDURE a; 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 INSERT INTO t1 (a) VALUES
(''), ('CENTRAL'), ('EASTERN'), ('GREATER LONDON'), (''), ('CENTRAL'), ('EASTERN'), ('GREATER LONDON'),
('NORTH CENTRAL'), ('NORTH EAST'), ('NORTH WEST'), ('SCOTLAND'), ('NORTH CENTRAL'), ('NORTH EAST'), ('NORTH WEST'), ('SCOTLAND'),
('SOUTH EAST'), ('SOUTH WEST'), ('WESTERN'); ('SOUTH EAST'), ('SOUTH WEST'), ('WESTERN');
EXPLAIN SELECT DISTINCT a,a FROM t1 ORDER BY a; EXPLAIN SELECT DISTINCT a,a FROM t1 ORDER BY a;
id select_type table type possible_keys key key_len ref rows Extra 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; SELECT DISTINCT a,a FROM t1 ORDER BY a;
a a a a
@ -2314,11 +2339,11 @@ t1;
id2 id3 id5 id4 id3 id6 id5 id1 id2 id3 id5 id4 id3 id6 id5 id1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
DROP TABLE t1,t2,t3,t4,t5,t6; 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); 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; 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 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; SELECT MAX(b), a FROM t1 WHERE b < 2 AND a = 1 GROUP BY a;
MAX(b) a MAX(b) a
1 1 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; 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; 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 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; SELECT MIN(c) FROM t2 WHERE b = 2 and a = 1 and c > 1 GROUP BY a;
MIN(c) MIN(c)
2 2
@ -2525,7 +2550,7 @@ a MIN(b) MAX(b) AVG(b)
2 1 3 2.0000 2 1 3 2.0000
1 1 3 2.0000 1 1 3 2.0000
DROP TABLE t1; 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 insert into t1 (a,b) values
(0,0),(0,1),(0,2),(0,3),(0,4),(0,5),(0,6), (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), (0,7),(0,8),(0,9),(0,10),(0,11),(0,12),(0,13),
@ -2597,7 +2622,7 @@ a b
3 13 3 13
explain extended select sql_buffer_result a, max(b)+1 from t1 where a = 0 group by a; 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 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: 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` 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; drop table t1;
@ -3547,7 +3572,7 @@ DROP TABLE t1,t2;
CREATE TABLE t1 ( CREATE TABLE t1 (
f1 int(11) NOT NULL DEFAULT '0', f1 int(11) NOT NULL DEFAULT '0',
f2 char(1) NOT NULL DEFAULT '', 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'), insert into t1 values(1,'A'),(1 , 'B'), (1, 'C'), (2, 'A'),
(3, 'A'), (3, 'B'), (3, 'C'), (3, 'D'); (3, 'A'), (3, 'B'), (3, 'C'), (3, 'D');
@ -3558,7 +3583,7 @@ f1 COUNT(DISTINCT f2)
3 4 3 4
explain SELECT f1, COUNT(DISTINCT f2) FROM t1 GROUP BY f1; explain SELECT f1, COUNT(DISTINCT f2) FROM t1 GROUP BY f1;
id select_type table type possible_keys key key_len ref rows Extra 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; drop table t1;
# End of test#50539. # End of test#50539.
# #
@ -3582,7 +3607,7 @@ INSERT INTO faulty (b, c) VALUES
EXPLAIN EXPLAIN
SELECT DISTINCT b, c FROM faulty WHERE b='1802' ORDER BY c; 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 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; SELECT DISTINCT b, c FROM faulty WHERE b='1802' ORDER BY c;
b c b c
1802 2013-02-28 09:00:00 1802 2013-02-28 09:00:00

20
mysql-test/t/group_min_max.test
View File

@ -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 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; 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 # Bug #16710: select distinct doesn't return all it should
@ -816,7 +828,7 @@ DROP PROCEDURE a;
# Bug #18068: SELECT DISTINCT # 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 INSERT INTO t1 (a) VALUES
(''), ('CENTRAL'), ('EASTERN'), ('GREATER LONDON'), (''), ('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 # 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); 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; 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 # Bug#38195: Incorrect handling of aggregate functions when loose index scan is
# used causes server crash. # 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 insert into t1 (a,b) values
(0,0),(0,1),(0,2),(0,3),(0,4),(0,5),(0,6), (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), (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 ( CREATE TABLE t1 (
f1 int(11) NOT NULL DEFAULT '0', f1 int(11) NOT NULL DEFAULT '0',
f2 char(1) NOT NULL DEFAULT '', 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'), insert into t1 values(1,'A'),(1 , 'B'), (1, 'C'), (2, 'A'),
(3, 'A'), (3, 'B'), (3, 'C'), (3, 'D'); (3, 'A'), (3, 'B'), (3, 'C'), (3, 'D');

8
sql/opt_range.cc
View File

@ -12411,8 +12411,12 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree, double read_time)
uchar cur_key_infix[MAX_KEY_LENGTH]; uchar cur_key_infix[MAX_KEY_LENGTH];
uint cur_used_key_parts; 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; goto next_index;
/* /*