MySQL分表优化

 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




[本日志由 admin 于 2012-02-25 01:13 PM 编辑]

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