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71.4. [Warning] Changed limits: max_open_files: 5000 (requested 20480)

		
2018-01-08T01:34:44.515973Z 0 [Warning] Changed limits: max_open_files: 5000 (requested 10240)
2018-01-08T01:34:44.516402Z 0 [Warning] Changed limits: table_open_cache: 1471 (requested 2000)		
		
		

提出出现在 CentOS 7 ulimit 配置没有问题的情况下mysql日志提示 Warning

			# ulimit -Sa | grep "open files"
			open files (-n) 40960
		
			[root@netkiller ~]# cat /proc/`pidof mysqld`/limits
			Limit Soft Limit Hard Limit Units
			Max cpu time unlimited unlimited seconds
			Max file size unlimited unlimited bytes
			Max data size unlimited unlimited bytes
			Max stack size 8388608 unlimited bytes
			Max core file size 0 unlimited bytes
			Max resident set unlimited unlimited bytes
			Max processes 63494 63494 processes
			Max open files 5000 5000 files
			Max locked memory 65536 65536 bytes
			Max address space unlimited unlimited bytes
			Max file locks unlimited unlimited locks
			Max pending signals 63494 63494 signals
			Max msgqueue size 819200 819200 bytes
			Max nice priority 0 0
			Max realtime priority 0 0
			Max realtime timeout unlimited unlimited us

		

动态改变

			[root@netkiller ~]# egrep '^(Limit|Max open files)' /proc/`pidof mysqld`/limits
			Limit Soft Limit Hard Limit Units
			Max open files 5000 5000 files
		

问题的出现出现原因是systemctl启动脚本覆盖了ulimit配置

			# cat /usr/lib/systemd/system/mysqld.service | grep -A2 open_files_limit
			# Sets open_files_limit
			LimitNOFILE = 5000
		

解决方法,直接修改上面的数值,不建议修改mysqld.service,这样会影响你下次升级。请采用下面的方案完美解决:

		
mkdir /usr/lib/systemd/system/mysqld.service.d

cat >> /usr/lib/systemd/system/mysqld.service.d/override.conf <<EOF
[Service]
LimitNOFILE=40960
EOF
		
		

重启 MySQL

			systemctl daemon-reload
			systemctl restart mysqld
		

检查是否生效

		
mysql> show variables like 'open_files_limit';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| open_files_limit | 65535 |
+------------------+-------+
1 row in set (0.01 sec)