MySQL内存使用的查看方式详解

前言

本文主要给大家介绍了关于mysql内存使用查看的相关内容，分享出来供大家参考学习，下面话不多说了，来一起看看详细的介绍吧

使用版本：mysql 5.7

在performance_schema有如下表记录内存使用情况

mysql> show tables like '%memory%summary%';
+-------------------------------------------------+
| tables_in_performance_schema (%memory%summary%) |
+-------------------------------------------------+
| memory_summary_by_account_by_event_name  |
| memory_summary_by_host_by_event_name  |
| memory_summary_by_thread_by_event_name  |
| memory_summary_by_user_by_event_name  |
| memory_summary_global_by_event_name  |
+-------------------------------------------------+

每个内存统计表都有如下统计列：

* count_alloc，count_free：对内存分配和释放内存函数的调用总次数

* sum_number_of_bytes_alloc，sum_number_of_bytes_free：已分配和已释放的内存块的总字节大小

* current_count_used：这是一个便捷列，等于count_alloc - count_free

* current_number_of_bytes_used：当前已分配的内存块但未释放的统计大小。这是一个便捷列，等于sum_number_of_bytes_alloc - sum_number_of_bytes_free

* low_count_used，high_count_used：对应current_count_used列的低和高水位标记

* low_number_of_bytes_used，high_number_of_bytes_used：对应current_number_of_bytes_used列的低和高水位标记

内存统计表允许使用truncate table语句。使用truncate语句时有如下行为：

* 通常，truncate操作会重置统计信息的基准数据（即清空之前的数据），但不会修改当前server的内存分配等状态。也就是说，truncate内存统计表不会释放已分配内存

 * 将count_alloc和count_free列重置，并重新开始计数（等于内存统计信息以重置后的数值作为基准数据）

* sum_number_of_bytes_alloc和sum_number_of_bytes_free列重置与count_alloc和count_free列重置类似

* low_count_used和high_count_used将重置为current_count_used列值

*  low_number_of_bytes_used和high_number_of_bytes_used将重置为current_number_of_bytes_used列值

* 此外，按照帐户，主机，用户或线程分类统计的内存统计表或memory_summary_global_by_event_name表，如果在对其依赖的accounts、hosts、users表执行truncate时，会隐式对这些内存统计表执行truncate语句

简单来说，就是可以根据用户、主机、线程、账号、全局的维度对内存进行监控。同时库sys也就这些表做了进一步的格式化，可以使得用户非常容易的观察到每个对象的内存开销：

mysql> select event_name,current_alloc from sys.memory_global_by_current_bytes limit 10;
+-----------------------------------------------------------------------------+---------------+
| event_name         | current_alloc |
+-----------------------------------------------------------------------------+---------------+
| memory/performance_schema/events_statements_history_long   | 13.66 mib |
| memory/performance_schema/events_statements_history_long.sqltext  | 9.77 mib |
| memory/performance_schema/events_statements_history_long.tokens  | 9.77 mib |
| memory/performance_schema/events_statements_summary_by_digest.tokens | 9.77 mib |
| memory/performance_schema/table_handles     | 9.06 mib |
| memory/performance_schema/events_statements_summary_by_thread_by_event_name | 8.67 mib |
| memory/sql/string::value       | 6.02 mib |
| memory/performance_schema/memory_summary_by_thread_by_event_name  | 5.62 mib |
| memory/performance_schema/events_statements_summary_by_digest  | 4.88 mib |
| memory/sql/table        | 4.35 mib |
+-----------------------------------------------------------------------------+---------------+

默认情况下performance_schema只对performance_schema进行了内存开销的统计。根据你的mysql安装代码区域可能包括performance_schema、sql、client、innodb、myisam、csv、memory、blackhole、archive、partition和其他。

查看innodb相关的内存监控是否开启，默认不开启

mysql> select * from performance_schema.setup_instruments
 -> where name like '%memory%';

+--------------------------------------------------------------------------------+---------+-------+
| name          | enabled | timed |
+--------------------------------------------------------------------------------+---------+-------+
| memory/performance_schema/mutex_instances     | yes | no |
| memory/performance_schema/rwlock_instances     | yes | no |
| memory/performance_schema/cond_instances     | yes | no |
| memory/performance_schema/file_instances     | yes | no |
| memory/performance_schema/socket_instances     | yes | no |
| memory/performance_schema/metadata_locks     | yes | no |
| memory/performance_schema/file_handle      | yes | no |
| memory/performance_schema/accounts      | yes | no |
| memory/performance_schema/events_waits_summary_by_account_by_event_name | yes | no |
| memory/performance_schema/events_stages_summary_by_account_by_event_name | yes | no |
| memory/performance_schema/events_statements_summary_by_account_by_event_name | yes | no |
| memory/performance_schema/events_transactions_summary_by_account_by_event_name | yes | no |
| memory/performance_schema/memory_summary_by_account_by_event_name  | yes | no |
| memory/performance_schema/events_stages_summary_global_by_event_name  | yes | no |
| memory/performance_schema/events_statements_summary_global_by_event_name | yes | no |
| memory/performance_schema/memory_summary_global_by_event_name   | yes | no |
| memory/performance_schema/hosts      | yes | no |
| memory/performance_schema/events_waits_summary_by_host_by_event_name  | yes | no |
| memory/performance_schema/events_stages_summary_by_host_by_event_name  | yes | no |
| memory/performance_schema/events_statements_summary_by_host_by_event_name | yes | no |
| memory/performance_schema/events_transactions_summary_by_host_by_event_name | yes | no |

可以通过条件缩小范围：

mysql> select * from performance_schema.setup_instruments
 where name like '%memory/innodb%';
+-------------------------------------------+---------+-------+
| name     | enabled | timed |
+-------------------------------------------+---------+-------+
| memory/innodb/adaptive hash index  | no | no |
| memory/innodb/buf_buf_pool  | no | no |
| memory/innodb/dict_stats_bg_recalc_pool_t | no | no |
| memory/innodb/dict_stats_index_map_t | no | no |
| memory/innodb/dict_stats_n_diff_on_level | no | no |
| memory/innodb/other   | no | no |
| memory/innodb/row_log_buf   | no | no |
| memory/innodb/row_merge_sort  | no | no |
| memory/innodb/std    | no | no |
| memory/innodb/trx_sys_t::rw_trx_ids | no | no |

对所有可能的对象进行内存监控。因此，还需要做下面的设置：

mysql> update performance_schema.setup_instruments set enabled = 'yes' where name like 'memory%';
query ok, 306 rows affected (0.00 sec)
rows matched: 376 changed: 306 warnings: 0

但是这种在线打开内存统计的方法仅对之后新增的内存对象有效，重启数据库后又会还原设置：

如想要对全局生命周期中的对象进行内存统计，必须在配置文件中进行设置，然后重启：

[mysqld]
performance-schema-instrument='memory/%=counted'

可以使用sys库下的memory_global_by_current_bytes表来查询相同的底层数据，该模式表显示了全局服务器内当前内存使用情况，按分配类型进行细分。

mysql> select * from sys.memory_global_by_current_bytes
 where event_name like 'memory/innodb/buf_buf_pool'\g
*************************** 1. row ***************************
 event_name: memory/innodb/buf_buf_pool
 current_count: 1
 current_alloc: 131.06 mib
current_avg_alloc: 131.06 mib
 high_count: 1
 high_alloc: 131.06 mib
 high_avg_alloc: 131.06 mib

此sys模式查询通过current_alloc()代码区域聚合当前分配的内存：

mysql> select substring_index(event_name,'/',2) as
 code_area, sys.format_bytes(sum(current_alloc))
 as current_alloc
 from sys.x$memory_global_by_current_bytes
 group by substring_index(event_name,'/',2)
 order by sum(current_alloc) desc;
+---------------------------+---------------+
| code_area   | current_alloc |
+---------------------------+---------------+
| memory/innodb  | 843.24 mib |
| memory/performance_schema | 81.29 mib |
| memory/mysys  | 8.20 mib |
| memory/sql  | 2.47 mib |
| memory/memory  | 174.01 kib |
| memory/myisam  | 46.53 kib |
| memory/blackhole  | 512 bytes |
| memory/federated  | 512 bytes |
| memory/csv  | 512 bytes |
| memory/vio  | 496 bytes |
+---------------------------+---------------+

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对的支持。