关于数据库:MySQL一次大量内存消耗的跟踪

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线上应用MySQL8.0.25的数据库，通过监控发现数据库在查问一个视图(80张表的union all)时内存和cpu均显著回升。

在8.0.25 MySQL Community Server官网版本测试发现：只能在视图上进行数据过滤，不能将视图上的过滤条件下推到视图内的表上进行数据过滤。8.0.29当前的版本已解决该问题。

MySQL视图拜访原理

上面是在8.0.25 MySQL Community Server上做的测试

应用sysbench 结构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)

创立视图

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;

查问视图

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 8.96 sec)

通过主键查问数据，查问返回4条数据，耗时1分8.96秒

查看执行打算

从执行打算上看，先对视图内的表进行全表扫描，最初在视图上过滤数据。

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     | <derived2> | NULL       | ref  | <auto_key0>   | <auto_key0> | 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)

增加hint后的执行打算

增加官网的 merge hint 进行视图合并(冀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)，不能扭转sql执行打算，优化器须要先进行全表扫描在对后果集进行过滤。sql语句的执行工夫根本不变

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     | <derived2> | NULL       | ref  | <auto_key0>   | <auto_key0> | 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)

创立视图(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 sbtest1 where id=1
      union all 
      select * from sbtest2 where id=1
     union all 
    select * from sbtest3  where id=1
     union all 
    select * from sbtest4 where id=1;
Query OK, 0 rows affected (0.02 sec)

查问视图(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)

间接运行sql语句

 mysql> select id ,k,left(c,20) from sbtest1 where id=1  
    ->  union all 
    ->  select id ,k,left(c,20) from sbtest2 where id=1  
    ->  union all 
    ->  select id ,k,left(c,20) from sbtest3 where id=1 
    ->  union all 
    ->  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)

间接运行sql语句或者把过滤条件放到视图内均能很快失去数据。

8.0.32

新的MySQL8.0.32版本已解决掉该问题，视图上的过滤条件能下推到表上。

 Server version: 8.0.32 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 🙂

## 对于 GreatSQL

GreatSQL是由万里数据库保护的MySQL分支，专一于晋升MGR可靠性及性能，反对InnoDB并行查问个性，是实用于金融级利用的MySQL分支版本。

相干链接： GreatSQL社区 Gitee GitHub Bilibili

GreatSQL社区：

社区博客有奖征稿详情：https://greatsql.cn/thread-100-1-1.html

技术交换群：

微信：扫码增加GreatSQL社区助手微信好友，发送验证信息加群。

关于数据库:MySQL一次大量内存消耗的跟踪

MySQL视图拜访原理

应用sysbench 结构4张1000000的表

手工收集表统计信息

创立视图

查问视图

通过主键查问数据，查问返回4条数据，耗时1分8.96秒

查看执行打算

增加hint后的执行打算

创立视图(过滤条件在视图内)

8.0.32

GreatSQL社区：

技术交换群：

评论

发表回复取消回复

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关于数据库:MySQL一次大量内存消耗的跟踪

MySQL视图拜访原理

应用sysbench 结构4张1000000的表

手工收集表统计信息

创立视图

查问视图

通过主键查问数据， 查问返回4条数据，耗时1分8.96秒

查看执行打算

增加hint后的执行打算

创立视图(过滤条件在视图内)

8.0.32

GreatSQL社区：

技术交换群：

评论

发表回复 取消回复

更多文章

苹果iOS打包的ipa应用无法安装？一篇文章带你了解可能的原因及排查方法

图解Golang：从零开始实现简易版过期LRU缓存

深入解析：基于Delta的线性数据结构模型，打造高效富文本编辑器

轻松管理社交媒体：使用Automa插件实现一键拉黑功能

通过主键查问数据，查问返回4条数据，耗时1分8.96秒

发表回复取消回复