今天发现线上服务挂了，排查发现是MySQL服务停了且重启失败，排查日志：

1）vim /var/log/mariadb/mariadb.log发现出现了Out of memory

240617 17:02:17 mysqld_safe mysqld from pid file /var/run/mariadb/mariadb.pid ended
240617 17:07:06 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
240617 17:07:06 [Note] /usr/libexec/mysqld (mysqld 5.5.60-MariaDB) starting as process 20263 ...
240617 17:07:06 [ERROR] mysqld: Out of memory (Needed 128917504 bytes)
240617 17:07:06 InnoDB: The InnoDB memory heap is disabled
240617 17:07:06 InnoDB: Mutexes and rw_locks use GCC atomic builtins
240617 17:07:06 InnoDB: Compressed tables use zlib 1.2.7
240617 17:07:06 InnoDB: Using Linux native AIO
240617 17:07:06 InnoDB: Initializing buffer pool, size = 256.0M
InnoDB: mmap(275513344 bytes) failed; errno 12
240617 17:07:06 InnoDB: Completed initialization of buffer pool
240617 17:07:06 InnoDB: Fatal error: cannot allocate memory for the buffer pool
240617 17:07:06 [ERROR] Plugin 'InnoDB' init function returned error.
240617 17:07:06 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
240617 17:07:07 [Note] Plugin 'FEEDBACK' is disabled.
240617 17:07:07 [ERROR] Unknown/unsupported storage engine: InnoDB
240617 17:07:07 [ERROR] Aborting 

2)查看系统内存占用，free -mh 发现系统内存已占满；

3）使用top分析，未看到内存占用高的进程，使用"ps aux --sort=-%mem | head -n 11"查看，发现有进程占用大量内存；

4）kill掉所有高占用内存（kill -9  $(ps -aux |grep 进程名 |awk '{print $2}')），重启MySQL成功。