MySQL -- 内存使用监控详解

问题：

　　1、我们怎么确定MySQL的各个部分分别使用了多少内存？

　　2、当有MySQL由于内存泄露引起OOM时、我们怎么提前发现？

怎么监控MySQL内存使用：

　　答案是通过performance_schema来完成、具体的做法如下：

第一步：配置performance_schema使它开启内存方面的监控

　　在/etc/my.cnf中增加如下内容

####  for performance_schema
performance_schema                                                      =on    #    on
performance_schema_consumer_events_stages_current                       =on    #    off
performance_schema_consumer_events_stages_history                       =on    #    off
performance_schema_consumer_events_stages_history_long                  =off   #    off
performance_schema_consumer_statements_digest                           =on    #    on
performance_schema_consumer_events_statements_current                   =on    #    on
performance_schema_consumer_events_statements_history                   =on    #    on
performance_schema_consumer_events_statements_history_long              =off   #    off
performance_schema_consumer_events_waits_current                        =on    #    off
performance_schema_consumer_events_waits_history                        =on    #    off
performance_schema_consumer_events_waits_history_long                   =off   #    off
performance_schema_consumer_global_instrumentation                      =on    #    on
performance_schema_consumer_thread_instrumentation                      =on    #    on
performance-schema-instrument                                           ='memory/%=COUNTED'

第二步：重启mysql数据库

systemctl restart mysql

　　这里要重启MySQL的主要是因为，许多的内存是在启动MySQL的时候就分配好了的，如果我们在MySQL启动完成后再通过

　　performance_schema.setup_instrument表来配置内存相关的监控的话，就是漏掉一些内存没有监控到。

第三步：通过performance_schema查询内存的使用情况

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             | 1.47 GiB      |
| memory/performance_schema | 131.51 MiB    |
| memory/mysys              | 8.22 MiB      |
| memory/sql                | 3.19 MiB      |
| memory/memory             | 213.15 KiB    |
| memory/myisam             | 171.79 KiB    |
| memory/csv                | 512 bytes     |
| memory/blackhole          | 512 bytes     |
+---------------------------+---------------+
8 rows in set (0.00 sec)