mysql内存占用过高的问题

现象：在mysql运行一天之后，发现内存占用量达到总内存的百分之77，且swap被占用百分之50

问题检查如下：

第一步：开启内存使用的监控服务

mysql> UPDATE performance_schema.setup_instruments SET ENABLED = 'YES' WHERE NAME LIKE 'memory/%';
 
 
禁用方法：
mysql> UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME LIKE 'memory/%';
 
查看方法：
mysql> select * from performance_schema.setup_instruments where NAME like 'memory%' and NAME not like 'memory/performance_schema%';
 
mysql> select * from performance_schema.setup_instruments where NAME like 'memory%';

第二步： 查看正常实例的使用情况

mysql> select USER,HOST,EVENT_NAME,COUNT_ALLOC,COUNT_FREE,CURRENT_COUNT_USED,SUM_NUMBER_OF_BYTES_ALLOC,SUM_NUMBER_OF_BYTES_FREE,CURRENT_NUMBER_OF_BYTES_USED from performance_schema.memory_summary_by_account_by_event_name order by CURRENT_NUMBER_OF_BYTES_USED desc limit 10;
 
COUNT_ALLOC：内存分配次数
COUNT_FREE：内存回收次数
SUM_NUMBER_OF_BYTES_ALLOC：内存分配大小
SUM_NUMBER_OF_BYTES_FREE：内存回收大小
CURRENT_COUNT_USED：当前分配的内存，通过COUNT_ALLOC-COUNT_FREE计算得到
CURRENT_NUMBER_OF_BYTES_USED：当前分配的内存大小，通过SUM_NUMBER_OF_BYTES_ALLOC-SUM_NUMBER_OF_BYTES_FREE计算得到
LOW_COUNT_USED：CURRENT_COUNT_USED的最小值
HIGH_COUNT_USED：CURRENT_COUNT_USED的最大值
LOW_NUMBER_OF_BYTES_USED：CURRENT_NUMBER_OF_BYTES_USED的最小值
HIGH_NUMBER_OF_BYTES_USED：CURRENT_NUMBER_OF_BYTES_USED的最大值

第三步： 查看内存监控表数据

 
mysql> select  substring_index(
    ->     substring_index(event_name, '/', 2),
    ->     '/',
    ->     -1
    ->   )  as event_type,
    ->   round(sum(CURRENT_NUMBER_OF_BYTES_USED)/1024/1024, 2) as MB_CURRENTLY_USED
    -> from performance_schema.memory_summary_global_by_event_name
    -> group by event_type

问题解决：

        当事件的内存占用是performance_schema过高的话，可以考虑关闭或者减少该事件使用内存的量，操作如下

降低performance_schema的内存使用率：
performance_schema_max_table_instances=400
table_definition_cache=400
table_open_cache=256
 
关闭performance_schema:
performance_schema=off