Mysql入门MySQL 分表优化试验代码

发布时间：2020-12-12 02:33:21 所属栏目：MySql教程来源：网络整理

导读：《Mysql入门MySQL 分表优化试验代码》要点：本文介绍了Mysql入门MySQL 分表优化试验代码，希望对您有用。如果有疑问，可以联系我们。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

《Mysql入门MySQL 分表优化试验代码》要点：
本文介绍了Mysql入门MySQL 分表优化试验代码，希望对您有用。如果有疑问，可以联系我们。

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 ',' 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.

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