首页 > 数据库 >重复索引检查mysql pt-duplicate-key-checker

重复索引检查mysql pt-duplicate-key-checker

时间：2023-09-02 22:02:35浏览次数：42  
标签：pt col2 duplicate col1 checker sbtest KEY TABLE sbtest1

索引对于优化数据库中的查询执行时间至关重要，但是索引数量过多或冗余会对性能产生负面影响。虽然pt-duplicate-key-checker是识别MySQL中重复或冗余索引的首选工具，但它可能无法捕获所有重复。

测试环境，mysql5.7.27

建表结

mysql [localhost:5727] {root} (sbtest) > CREATE TABLE `sbtest1` (
    -> `id` int NOT NULL,
    -> `col1` varchar(1) DEFAULT NULL,
    -> `col2` varchar(2) DEFAULT NULL,
    -> `col3` varchar(3) DEFAULT NULL,
    -> `col4` varchar(4) DEFAULT NULL,
    -> PRIMARY KEY (`id`),
    -> UNIQUE KEY `id` (`id`),
    -> UNIQUE KEY `col1` (`col1`,`col2`),
    -> UNIQUE KEY `col2` (`col2`,`col1`),
    -> UNIQUE KEY `col1_2` (`col1`,`col2`),
    -> UNIQUE KEY `col1_3` (`col1`,`col2`,`col3`),
    -> UNIQUE KEY `col1_4` (`col1`),
    -> UNIQUE KEY `col1_5` (`col1`),
    -> KEY `idx1` (`col1`,`id`),
    -> KEY `idx2` (`col1`,`col2`),
    -> KEY `idx3` (`col2`,`col1`),
    -> KEY `idx4` (`col1`,`col2`,`col3`),
    -> KEY `idx5` (`col1`,`col2`)
    -> ) ENGINE=InnoDB;
Query OK, 0 rows affected, 3 warnings (0.02 sec)

运行pt-duplicate-key-checker工具，多余的索引会给出相应的解决方案

[root@testdb ~]# pt-duplicate-key-checker --user=root --password=msandbox  --port=5727 --socket=/tmp/mysql_sandbox5727.sock --databases sbtest --tables sbtest1
# ########################################################################
# sbtest.sbtest1
# ########################################################################
 
# Uniqueness of id ignored because PRIMARY is a duplicate constraint
# id is a duplicate of PRIMARY
# Key definitions:
#   UNIQUE KEY `id` (`id`),
#   PRIMARY KEY (`id`),
# Column types:
#         `id` int(11) not null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `id`;
 
# Uniqueness of col1_4 ignored because col1_5 is a duplicate constraint
# col1_4 is a duplicate of col1_5
# Key definitions:
#   UNIQUE KEY `col1_4` (`col1`),
#   UNIQUE KEY `col1_5` (`col1`),
# Column types:
#         `col1` varchar(1) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `col1_4`;
 
# idx3 is a duplicate of col2
# Key definitions:
#   KEY `idx3` (`col2`,`col1`),
#   UNIQUE KEY `col2` (`col2`,`col1`),
# Column types:
#         `col2` varchar(2) default null
#         `col1` varchar(1) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx3`;
 
# idx4 is a duplicate of col1_3
# Key definitions:
#   KEY `idx4` (`col1`,`col2`,`col3`),
#   UNIQUE KEY `col1_3` (`col1`,`col2`,`col3`),
# Column types:
#         `col1` varchar(1) default null
#         `col2` varchar(2) default null
#         `col3` varchar(3) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx4`;
 
# Uniqueness of col1 ignored because col1_5 is a stronger constraint
# col1 is a left-prefix of col1_3
# Key definitions:
#   UNIQUE KEY `col1` (`col1`,`col2`),
#   UNIQUE KEY `col1_3` (`col1`,`col2`,`col3`),
# Column types:
#         `col1` varchar(1) default null
#         `col2` varchar(2) default null
#         `col3` varchar(3) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `col1`;
 
# Uniqueness of col1_2 ignored because col1_5 is a stronger constraint
# col1_2 is a left-prefix of col1_3
# Key definitions:
#   UNIQUE KEY `col1_2` (`col1`,`col2`),
#   UNIQUE KEY `col1_3` (`col1`,`col2`,`col3`),
# Column types:
#         `col1` varchar(1) default null
#         `col2` varchar(2) default null
#         `col3` varchar(3) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `col1_2`;
 
# idx2 is a left-prefix of col1_3
# Key definitions:
#   KEY `idx2` (`col1`,`col2`),
#   UNIQUE KEY `col1_3` (`col1`,`col2`,`col3`),
# Column types:
#         `col1` varchar(1) default null
#         `col2` varchar(2) default null
#         `col3` varchar(3) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx2`;
 
# idx5 is a left-prefix of col1_3
# Key definitions:
#   KEY `idx5` (`col1`,`col2`)
#   UNIQUE KEY `col1_3` (`col1`,`col2`,`col3`),
# Column types:
#         `col1` varchar(1) default null
#         `col2` varchar(2) default null
#         `col3` varchar(3) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx5`;
 
# Key idx1 ends with a prefix of the clustered index
# Key definitions:
#   KEY `idx1` (`col1`,`id`),
#   PRIMARY KEY (`id`),
# Column types:
#         `col1` varchar(1) default null
#         `id` int(11) not null
# To shorten this duplicate clustered index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx1`, ADD INDEX `idx1` (`col1`);
 
# ########################################################################
# Summary of indexes
# ########################################################################
 
# Size Duplicate Indexes   76
# Total Duplicate Indexes  9
# Total Indexes            13

再执行pt-duplicate-key-checker给出的解决方案

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `id`;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `col1_4`;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx3`;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx4`;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `col1`;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `col1_2`;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx2`;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx5`;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql [localhost:5727] {root} (sbtest) > ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx1`, ADD INDEX `idx1` (`col1`);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

检查表结构：

mysql [localhost:5727] {root} (sbtest) > show create table `sbtest`.`sbtest1`\G
*************************** 1. row ***************************
       Table: sbtest1
Create Table: CREATE TABLE `sbtest1` (
  `id` int(11) NOT NULL,
  `col1` varchar(1) DEFAULT NULL,
  `col2` varchar(2) DEFAULT NULL,
  `col3` varchar(3) DEFAULT NULL,
  `col4` varchar(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `col2` (`col2`,`col1`),
  UNIQUE KEY `col1_3` (`col1`,`col2`,`col3`),
  UNIQUE KEY `col1_5` (`col1`),
  KEY `idx1` (`col1`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

 检查发现没有多余的索引。 

再对表加一个唯一索引

mysql [localhost:5727] {root} (sbtest) > alter table sbtest1 add UNIQUE KEY col2_1(col1,col2);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql [localhost:5727] {root} (sbtest) > alter table sbtest1 drop index col1_3;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql [localhost:5727] {root} (sbtest) > show create table `sbtest`.`sbtest1`\G
*************************** 1. row ***************************
       Table: sbtest1
Create Table: CREATE TABLE `sbtest1` (
  `id` int(11) NOT NULL,
  `col1` varchar(1) DEFAULT NULL,
  `col2` varchar(2) DEFAULT NULL,
  `col3` varchar(3) DEFAULT NULL,
  `col4` varchar(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `col2` (`col2`,`col1`),
  UNIQUE KEY `col1_5` (`col1`),
  UNIQUE KEY `col2_1` (`col1`,`col2`),
  KEY `idx1` (`col1`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

这里人为可以看出索引col2和 col2_1是重复的，再用 pt-duplicate-key-checker工具检查看看看能不能查出来

[root@testdb ~]# pt-duplicate-key-checker --user=root --password=msandbox  --port=5727 --socket=/tmp/mysql_sandbox5727.sock --databases sbtest --tables sbtest1
# ########################################################################
# sbtest.sbtest1
# ########################################################################
 
# idx1 is a duplicate of col1_5
# Key definitions:
#   KEY `idx1` (`col1`)
#   UNIQUE KEY `col1_5` (`col1`),
# Column types:
#         `col1` varchar(1) default null
# To remove this duplicate index, execute:
ALTER TABLE `sbtest`.`sbtest1` DROP INDEX `idx1`;
 
# ########################################################################
# Summary of indexes
# ########################################################################
 
# Size Duplicate Indexes   4
# Total Duplicate Indexes  1
# Total Indexes            5

检查发出是索引IDX1有重复，并没有检查出col2和col2_1重复。当这种重复索引检查不出时，只能通过自定义SQL来检查。

mysql [localhost:5727] {root} (sbtest) > SELECT DISTINCT TABLE_SCHEMA, TABLE_NAME, group_concat(INDEX_NAME) duplic8_UK, COLUMN_NAMES FROM
    ->  (SELECT DISTINCT TABLE_SCHEMA, TABLE_NAME, INDEX_NAME, GROUP_CONCAT(COLUMN_NAME ORDER BY COLUMN_NAME SEPARATOR ',') AS COLUMN_NAMES
    ->  FROM information_schema.STATISTICS WHERE NON_UNIQUE = 0 AND INDEX_NAME!='PRIMARY' AND INDEX_TYPE = 'BTREE'
    ->  GROUP BY TABLE_SCHEMA, TABLE_NAME, INDEX_NAME) X group by TABLE_SCHEMA, TABLE_NAME, COLUMN_NAMES having count(*)> 1;
+--------------+------------+-------------+--------------+
| TABLE_SCHEMA | TABLE_NAME | duplic8_UK  | COLUMN_NAMES |
+--------------+------------+-------------+--------------+
| sbtest       | sbtest1    | col2,col2_1 | col1,col2    |
+--------------+------------+-------------+--------------+
1 row in set (0.09 sec)

 从自定义的SQL脚本可以看到，索引col2和col2_1是重复的。

 当pt工具检查索引不全时，可以用自定义SQL脚本检查。

标签：pt,col2,duplicate,col1,checker,sbtest,KEY,TABLE,sbtest1
From： https://blog.51cto.com/u_13482808/7335026

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