mysql内存占用过高的问题

2023-09-01 06:26

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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

select event_name, current_alloc, high_alloc from sys.memory_global_by_current_bytes where current_count > 0;

第三步：查看事件类型下的内存量

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=400table_definition_cache=400table_open_cache=256关闭performance_schema:performance_schema=off