MySQL内存使用的查看方式详解

前言

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使用版本：MySQL 5.7

官方文档

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

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