首先先查看内存空间的使用情况命令:free -m然后进行释放操作命令:sync; echo 3 > /proc/sys/vm/drop_caches最后查看内存的情况发现已清理（本人linux的系统7.5）。好文要顶 关注我 收藏该文 

[13223] 17 Mar 13:18:02.207 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add '

查询 id = 6 的所有父级SELECT ID.level, DATA.* FROM( SELECT @id as _id, ( SELECT @id := parent_id FROM table1 WHERE id = @id ) as _pid, @l := @l