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)
1、从上面的结果我们可以知道innodb、performance_schema、mysys ... 它们共用了多少内存了、如果某一类组件的内存使用没有节制的增长上去、多半
它就是内存泄露了。 对于这种情况只能是升级MySQL到更高的版本了。
目前performance-schema相关的配置模板已经增加到mysqltools当中
https://github.com/Neeky/mysqltools/blob/master/deploy/ansible/mysql/template/5.7/my.cnf
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