MySQL性能優化（一）慢日誌開啓

1、開啓慢日誌的參數，永久生效果。在my.cnf添加如下參數。

[mysqld]
slow_query_log           = 1
slow_query_log_file      = /xxx/mysql-slow.log
long_query_time          = 1

2、一般這樣會開啓失敗，mysql日誌報錯：Errcode: 13 - Permission denied

mysqld: File '/var/log/mysql/mysql-slow.log' not found (Errcode: 13 - Permission denied)
2019-11-02T03:13:42.567891Z 0 [ERROR] Could not use /var/log/mysql/mysql-slow.log for logging (error 13 - Permission denied). Turning logging off for the server process. To turn it on again: fix the cause, then either restart the query logging by using "SET GLOBAL SLOW_QUERY_LOG=ON" or restart the MySQL server.

產生原因：mysql沒有文件讀寫權限

解決措施：其次permission denied 主要是因爲 目錄權限

    chmod /xxx 777

    chown -R mysql /xxx

    chgrp -R mysql /xxx

3、systemctl restart mysqld 重啓mysql即可。