my.cnf 无法修改连接数，报错信息：
[Warning] Buffered warning: Changed limits: max_open_files: 1024 (requested 15000)
[Warning] Buffered warning: Changed limits: max_connections: 214 (requested 3000)
[Warning] Buffered warning: Changed limits: table_open_cache: 400 (requested 1520)
修改/etc/security/limits.conf
添加：
mysql hard nofile 65535
mysql soft nofile 65535
vi /usr/lib/systemd/system/mysqld.service.d/limits.conf #创建并配置配置文件
[Service]
LimitNOFILE=10000
# 重新加载配置文件
systemctl daemon-reload
#重启mysqld服务，使配置生效。
systemctl restart mysqld.service