MySQL分表优化试验

我们的项目中有好多不等于的情况。今天写这篇文章简单的分析一下怎么个优化法。这里的分表逻辑是根据t_group表的user_name组的个数来分的。因为这种情况单独user_name字段上的索引就属于烂索引。起不了啥名明显的效果。

1、试验PROCEDURE.DELIMITER $$DROP PROCEDURE `t_girl`.`sp_split_table`$$CREATE; PROCEDURE `t_girl`.`sp_split_table`()BEGIN declare done int default 0; declare v_user_name varchar(20) default ''; declare v_table_name varchar(64) default ''; -- Get all users' name. declare cur1 cursor for select user_name from t_group group by user_name; -- Deal with error or warnings. declare continue handler for 1329 set done = 1; -- Open cursor. open cur1; while done <> 1 do fetch cur1 into v_user_name; if not done then -- Get table name. set v_table_name = concat('t_group_',v_user_name); -- Create new extra table. set @stmt = concat('create table ',v_table_name,' like t_group'); prepare s1 from @stmt; execute s1; drop prepare s1; -- Load data into it. set @stmt = concat('insert into ',v_table_name,' select * from t_group where user_name = ''',v_user_name,''''); prepare s1 from @stmt; execute s1; drop prepare s1; end if; end while; -- Close cursor. close cur1; -- Free variable from memory. set @stmt = NULL;END$$

DELIMITER ;

2、试验表。我们用一个有一千万条记录的表来做测试。

mysql> select count(*) from t_group;+----------+| count(*) |+----------+| 10388608 |+----------+1 row in set (0.00 sec)

表结构。mysql> desc t_group;+-------------+------------------+------+-----+-------------------+----------------+| Field;;;;| Type;;| Null | Key | Default| Extra; |+-------------+------------------+------+-----+-------------------+----------------+| id; | int(10) unsigned | NO| PRI | NULL;;;| auto_increment || money;;;;| decimal(10,2);| NO|;;||;;;;;|| user_name| varchar(20);;;| NO| MUL ||;;;;;|| create_time | timestamp;;;;;| NO|;;| CURRENT_TIMESTAMP |;;;;;|+-------------+------------------+------+-----+-------------------+----------------+4 rows in set (0.00 sec)

索引情况。

mysql> show index from t_group;+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+|Table| Non_unique | Key_name | Seq_in_index | Column_name |Collation | Cardinality | Sub_part | Packed | Null | Index_type |Comment |+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+|t_group |; 0 | PRIMARY; |;1 | id; |A |;10388608 |;;NULL | NULL|;;;| BTREE;;| || t_group |; 1 | idx_user_name;|1 | user_name| A |8 |;;NULL | NULL|;;;|BTREE;;;| || t_group |; 1 | idx_combination1|;1 | user_name| A |8 |;;NULL |NULL|;;;| BTREE;;;| || t_group |; 1 |idx_combination1 |;2 | money;;;;| A |;;;;;3776|;;NULL | NULL|;;;| BTREE;;;| |+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+4 rows in set (0.00 sec)

PS:idx_combination1 这个索引是必须的，因为要对user_name来GROUP BY。此时属于松散索引扫描！当然完了后你可以干掉她。idx_user_name 这个索引是为了加快单独执行constant这种类型的查询。我们要根据用户名来分表。

mysql> select user_name from t_group where 1 group by user_name;+-----------+| user_name |+-----------+| david;;|| leo;;;;|| livia;;|| lucy;;;|| sarah;;|| simon;;|| sony;;;|| sunny;;|+-----------+8 rows in set (0.00 sec)

所以结果表应该是这样的。mysql> show tables like 't_group_%';+------------------------------+| Tables_in_t_girl (t_group_%) |+------------------------------+| t_group_david;;;;;|| t_group_leo; || t_group_livia;;;;;|| t_group_lucy || t_group_sarah;;;;;|| t_group_simon;;;;;|| t_group_sony || t_group_sunny;;;;;|+------------------------------+8 rows in set (0.00 sec)

3、对比结果。

mysql> select count(*) from t_group where user_name = 'david';+----------+| count(*) |+----------+|; 1298576 |+----------+1 row in set (1.71 sec)

执行了将近2秒。

mysql> select count(*) from t_group_david;+----------+| count(*) |+----------+|; 1298576 |+----------+1 row in set (0.00 sec)几乎是瞬间的。

mysql> select count(*) from t_group where user_name <> 'david';+----------+| count(*) |+----------+|; 9090032 |+----------+1 row in set (9.26 sec)执行了将近10秒，可以想象，这个是实际的项目中是不能忍受的。mysql> select (select count(*) from t_group) - (select count(*) from t_group_david) as total;+---------+| total|+---------+| 9090032 |+---------+1 row in set (0.00 sec)几乎是瞬间的。

我们来看看聚集函数。对于原表的操作。

mysql> select min(money),max(money) from t_group where user_name = 'david';+------------+------------+| min(money) | max(money) |+------------+------------+|;;;-6.41 |;;500.59 |+------------+------------+1 row in set (0.00 sec)最小，最大值都是FULL INDEX SCAN。所以是瞬间的。mysql> select sum(money),avg(money) from t_group where user_name = 'david';+--------------+------------+| sum(money)| avg(money) |+--------------+------------+| 319992383.84 | 246.417910 |+--------------+------------+1 row in set (2.15 sec)其他聚集函数的结果就不是FULL INDEX SCAN了。耗时2.15秒。

对于小表的操作。mysql> select min(money),max(money) from t_group_david;+------------+------------+| min(money) | max(money) |+------------+------------+|;;;-6.41 |;;500.59 |+------------+------------+1 row in set (1.50 sec)最大最小值完全是FULL TABLE SCAN,耗时1.50秒，不划算。以此看来。mysql> select sum(money),avg(money) from t_group_david;+--------------+------------+| sum(money)| avg(money) |+--------------+------------+| 319992383.84 | 246.417910 |+--------------+------------+1 row in set (1.68 sec)

取得这两个结果也是花了快2秒，快了一点。

我们来看看这个小表的结构。mysql> desc t_group_david;+-------------+------------------+------+-----+-------------------+----------------+| Field;;;;| Type;;| Null | Key | Default| Extra; |+-------------+------------------+------+-----+-------------------+----------------+| id; | int(10) unsigned | NO| PRI | NULL;;;| auto_increment || money;;;;| decimal(10,2);| NO|;;||;;;;;|| user_name| varchar(20);;;| NO| MUL ||;;;;;|| create_time | timestamp;;;;;| NO|;;| CURRENT_TIMESTAMP |;;;;;|+-------------+------------------+------+-----+-------------------+----------------+4 rows in set (0.00 sec)

明显的user_name属性是多余的。那么就干掉它。mysql> alter table t_group_david drop user_name;Query OK, 1298576 rows affected (7.58 sec)Records: 1298576; Duplicates: 0; Warnings: 0

现在来重新对小表运行查询

mysql> select min(money),max(money) from t_group_david;+------------+------------+| min(money) | max(money) |+------------+------------+|;;;-6.41 |;;500.59 |+------------+------------+1 row in set (0.00 sec)

此时是瞬间的。mysql> select sum(money),avg(money) from t_group_david;+--------------+------------+| sum(money)| avg(money) |+--------------+------------+| 319992383.84 | 246.417910 |+--------------+------------+1 row in set (0.94 sec)

这次算是控制在一秒以内了。

mysql> Aborted

小总结一下：分出的小表的属性尽量越少越好。大胆的去干吧。