近日使用mysql時遇到了一個問題，就是mysql一直無法正常啟動，經過多次嘗試，依然重啟不了。通過排查，最終找到了問題所在。

Error log：
2021-10-25T07:22:47.267770Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.32) starting as process 20747 ...
2021-10-25T07:22:47.269956Z 0 [Note] InnoDB: PUNCH HOLE support available
2021-10-25T07:22:47.269976Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2021-10-25T07:22:47.269984Z 0 [Note] InnoDB: Uses event mutexes
2021-10-25T07:22:47.269988Z 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
2021-10-25T07:22:47.269991Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
2021-10-25T07:22:47.269993Z 0 [Note] InnoDB: Using Linux native AIO
2021-10-25T07:22:47.270071Z 0 [Note] InnoDB: Number of pools: 1
2021-10-25T07:22:47.270114Z 0 [Note] InnoDB: Using CPU crc32 instructions
2021-10-25T07:22:47.271128Z 0 [ERROR] InnoDB: mmap(137458688 bytes) failed; errno 12
2021-10-25T07:22:47.271150Z 0 [ERROR] InnoDB: Cannot allocate memory for the buffer pool
2021-10-25T07:22:47.271154Z 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error
2021-10-25T07:22:47.271157Z 0 [ERROR] Plugin 'InnoDB' init function returned error.
2021-10-25T07:22:47.271159Z 0 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2021-10-25T07:22:47.271162Z 0 [ERROR] Failed to initialize plugins.
2021-10-25T07:22:47.271165Z 0 [ERROR] Aborting
mysql啟動失敗原因為InnoDB的buffer pool無法分配足夠內存，導致執行初始化步驟失敗。

解決方法：

在/etc/mysql/my.cnf文件中，進行如下修改：

#innodb_buffer_pool_size = 1G
innodb_buffer_pool_size = 128M

將innodb_buffer_pool_size的原先值進行縮小，重新啟動mysql，此時mysql已可以正常啟動。

通過以上操作，成功解決了mysql啟動失敗的問題，同時注意到InnoDB的buffer pool預分配內存的值應該按照實際情況進行調整。