mysql报错Changed limits: max_open_files: 5000

OS:CentOS 7.4 DB:mysql 5.7.17 error.log日志里报错信息：

1. 2018-04-08T09:52:52.641263Z 0 [Warning] Changed limits: max_open_files: 5000 (requested 50000)
2. 2018-04-08T09:52:52.641467Z 0 [Warning] Changed limits: max_connections: 4190 (requested 10000)
3. 2018-04-08T09:52:52.641476Z 0 [Warning] Changed limits: table_open_cache: 400 (requested 2000)

看到这个错误第一反应是去数据库查查当前的参数都是多少，和日志里提示的是一样的

1. mysql> show variables like '%files%';
2. +---------------------------+--------+
3. | Variable_name | Value |
4. +---------------------------+--------+
5. | character_set_filesystem | binary |
6. | innodb_log_files_in_group | 2 |
7. | innodb_open_files | 400 |
8. | keep_files_on_create | OFF |
9. | large_files_support | ON |
10. | open_files_limit | 5000 |
11. +---------------------------+--------+
12. 6 rows in set (0.00 sec)
14. mysql> show variables like '%connections%';
15. +----------------------+-------+
16. | Variable_name | Value |
17. +----------------------+-------+
18. | max_connections | 4190 |
19. | max_user_connections | 0 |
20. +----------------------+-------+
21. 2 rows in set (0.00 sec)
24. mysql> show variables like '%table_open_cache%';
25. +----------------------------+-------+
26. | Variable_name | Value |
27. +----------------------------+-------+
28. | table_open_cache | 400 |
29. | table_open_cache_instances | 16 |
30. +----------------------------+-------+
31. 2 rows in set (0.01 sec)

看到是max_open_files，难道是操作系统限制了？也没有啊

1. [root@iz2ze6jo3o3bqbcongnypoz mysql]# ulimit -n
2. 65535

my.cnf文件里也没有对这些参数做修改，因为是用mysqld.service启动的，难道是这个文件的问题吗？

1. [root@iz2ze6jo3o3bqbcongnypoz system]# more /usr/lib/systemd/system/mysqld.service 
2. # Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
3. #
4. # This program is free software; you can redistribute it and/or modify
5. # it under the terms of the GNU General Public License as published by
6. # the Free Software Foundation; version 2 of the License.
7. #
8. # This program is distributed in the hope that it will be useful,
9. # but WITHOUT ANY WARRANTY; without even the implied warranty of
10. # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11. # GNU General Public License for more details.
12. #
13. # You should have received a copy of the GNU General Public License
14. # along with this program; if not, write to the Free Software
15. # Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
16. #
17. # systemd service file for MySQL forking server
18. #
20. [Unit]
21. Description=MySQL Server
22. Documentation=man:mysqld(8)
23. Documentation=http://dev.mysql.com/doc/refman/en/using-systemd.html
24. After=network.target
25. After=syslog.target
27. [Install]
28. WantedBy=multi-user.target
30. [Service]
31. User=mysql
32. Group=mysql
34. Type=forking
36. PIDFile=/var/run/mysqld/mysqld.pid
38. # Disable service start and stop timeout logic of systemd for mysqld service.
39. TimeoutSec=0
41. # Execute pre and post scripts as root
42. PermissionsStartOnly=true
44. # Needed to create system tables
45. ExecStartPre=/usr/bin/mysqld_pre_systemd
47. # Start main service
48. ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS
50. # Use this to switch malloc implementation
51. EnvironmentFile=-/etc/sysconfig/mysql
53. # Sets open_files_limit
54. LimitNOFILE = 5000

果然是...把这个参数修改为65535后，重启mysql，问题消失了。

1. LimitNOFILE = 5000 这个值默认就是5000，下面这篇文档说清楚这个事了：

https://dev.mysql.com/doc/refman/5.7/en/using-systemd.html

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