MySQL一次大量内存消耗的跟踪

GreatSQL是MySQL的国产分支版本,使用上与MySQL一致.

MySQL视图访问原理

使用sysbench 构造4张1000000的表

 mysql> select count(*) from sbtest1;

+----------+
| count(*) |
+----------+
|  1000000 |
+----------+

1 row in set (1.44 sec)
mysql> show create table sbtest1;

| Table   | Create Table  | sbtest1 | 
CREATE TABLE +sbtest1+ (

  +id+ int NOT NULL AUTO_INCREMENT,

  +k+ int NOT NULL DEFAULT '0',

  +c+ char(120) COLLATE utf8mb4_0900_bin NOT NULL DEFAULT '',

  +pad+ char(60) COLLATE utf8mb4_0900_bin NOT NULL DEFAULT '',

  PRIMARY KEY (+id+)

) ENGINE=InnoDB AUTO_INCREMENT=2000000 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_bin |

+---------+-----------------------------------------------------------------------------------
1 row in set (0.00 sec)

手工收集表统计信息

mysql> analyze table sbtest1,sbtest2 ,sbtest3,sbtest4;

+----------------+---------+----------+----------+
| Table          | Op      | Msg_type | Msg_text |
+----------------+---------+----------+----------+
| sbtest.sbtest1 | analyze | status   | OK       |
| sbtest.sbtest2 | analyze | status   | OK       |
| sbtest.sbtest3 | analyze | status   | OK       |
| sbtest.sbtest4 | analyze | status   | OK       |
+----------------+---------+----------+----------+

4 rows in set (0.17 sec)

创建视图

drop view view_sbtest1 ;

Create view view_sbtest1  as 

select * from sbtest1 
union all 
select * from sbtest2 
union all 
select * from sbtest3 
union all 
select * from sbtest4;

查询视图

Select * from view_sbtest1 where id=1;

 mysql> Select id ,k,left(c,20) from view_sbtest1 where id=1;
+----+--------+----------------------+
| id | k      | left(c,20)           |
+----+--------+----------------------+
|  1 | 434041 | 61753673565-14739672 |
|  1 | 501130 | 64733237507-56788752 |
|  1 | 501462 | 68487932199-96439406 |
|  1 | 503019 | 18034632456-32298647 |
+----+--------+----------------------+
4 rows in set (1 min ⑧96 sec)

通过主键查询数据, 查询返回4条数据,耗时1分⑧96秒

查看执行计划

从执行计划上看,先对视图内的表进行全表扫描,最后在视图上过滤数据.

mysql> explain Select id ,k,left(c,20) from view_sbtest1 where id=1;
+----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+-------+
| id | select_type | table      | partitions | type | possible_keys | key         | key_len | ref   | rows   | filtered | Extra |
+----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+-------+
|  1 | PRIMARY     |  | NULL       | ref  |    |  | 4       | const |     10 |   100.00 | NULL  |
|  2 | DERIVED     | sbtest1    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
|  3 | UNION       | sbtest2    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
|  4 | UNION       | sbtest3    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
|  5 | UNION       | sbtest4    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
+----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+-------+
5 rows in set, 1 warning (0.07 sec)  

添加hint后的执行计划

添加官方的 merge hint 进行视图合并(期望视图不作为一个整体,让where上的过滤条件能下推到视图中的表),不能改变sql执行计划,优化器需要先进行全表扫描在对结果集进行过滤.sql语句的执行时间基本不变

mysql> explain Select /*+  merge(t1) */ id ,k,left(c,20) from view_sbtest1 t1 where id=1;
+----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+-------+
| id | select_type | table      | partitions | type | possible_keys | key         | key_len | ref   | rows   | filtered | Extra |
+----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+-------+
|  1 | PRIMARY     |  | NULL       | ref  |    |  | 4       | const |     10 |   100.00 | NULL  |
|  2 | DERIVED     | sbtest1    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
|  3 | UNION       | sbtest2    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
|  4 | UNION       | sbtest3    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
|  5 | UNION       | sbtest4    | NULL       | ALL  | NULL          | NULL        | NULL    | NULL  | 986400 |   100.00 | NULL  |
+----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+-------+
5 rows in set, 1 warning (0.00 sec)

创建视图(过滤条件在视图内)

mysql> drop view view_sbtest3;
ERROR 1051 (42S02): Unknown table 'sbtest.view_sbtest3'
mysql> Create view view_sbtest3 as 
select * from sbtest4 where id=1;
Query OK, 0 rows affected (0.02 sec)

查询视图(过滤条件在视图上)

Select id ,k,left(c,20) from view_sbtest3 where id=1;

mysql>  Select id ,k,left(c,20) from view_sbtest3 where id=1;
+----+--------+----------------------+
| id | k      | left(c,20)           |
+----+--------+----------------------+
|  1 | 501462 | 68487932199-96439406 |
|  1 | 434041 | 61753673565-14739672 |
|  1 | 501130 | 64733237507-56788752 |
|  1 | 503019 | 18034632456-32298647 |
+----+--------+----------------------+
4 rows in set (0.01 sec)

直接运行sql语句

 mysql> select id ,k,left(c,20) from sbtest1 where id=1  
->  select id ,k,left(c,20) from sbtest4 where id=1;
+----+--------+----------------------+
| id | k      | left(c,20)           |
+----+--------+----------------------+
|  1 | 501462 | 68487932199-96439406 |
|  1 | 434041 | 61753673565-14739672 |
|  1 | 501130 | 64733237507-56788752 |
|  1 | 503019 | 18034632456-32298647 |
+----+--------+----------------------+
4 rows in set (0.01 sec)

直接运行sql语句或者把过滤条件放到视图内均能很快得到数据.

⑧0.32

 Server version: ⑧0.32 MySQL Community Server - GPL

Copyright (c) 2000, 2023, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use sbtest;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> Select id ,k,left(c,20) from view_sbtest1 where id=1;
+----+--------+----------------------+
| id | k      | left(c,20)           |
+----+--------+----------------------+
|  1 | 501462 | 68487932199-96439406 |
|  1 | 434041 | 61753673565-14739672 |
|  1 | 501130 | 64733237507-56788752 |
|  1 | 503019 | 18034632456-32298647 |
+----+--------+----------------------+
4 rows in set (0.01 sec)

mysql> Select id ,k,left(c,20) from view_sbtest3 where id=1;
+----+--------+----------------------+
| id | k      | left(c,20)           |
+----+--------+----------------------+
|  1 | 501462 | 68487932199-96439406 |
|  1 | 434041 | 61753673565-14739672 |
|  1 | 501130 | 64733237507-56788752 |
|  1 | 503019 | 18034632456-32298647 |
+----+--------+----------------------+
4 rows in set (0.00 sec)

Enjoy GreatSQL ?

关于 GreatSQL

GreatSQL是由万里数据库维护的MySQL分支,专注于提升MGR可靠性及性能,支持InnoDB并行查询特性,是适用于金融级应用的MySQL分支版本.

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