Question

I was wondering if there’s a way to decrease the opened files in mysql.

Details :

• mysql 5.0.92

• engine used : MyISAM

• SHOW GLOBAL STATUS LIKE ‘Opened_tables’ : 150K

• SHOW VARIABLES LIKE ‘%open%’ :

      open_files_limit    200000
      table_open_cache    40000
  

Solutions tried :

• restart server : it works the opened tables counter is 0 but this isn’t a good solution from my pov since you will need a restart every week because the counter will increase fast

• FLUSH TABLES : like the mysql doc said it should force all tables in use to close but this doesn’t happen

So any thoughts on this matter?

Answer 1

Generally, many open tables are nothing to worry about. If you come close to OS limits, you can increase this limits in the kernel settings:

How do I change the number of open files limit in Linux?

MySQL opens tables for each session independently to have better concurrency.

The table_open_cache and max_connections system variables affect the maximum number of files the server keeps open. If you increase one or both of these values, you may run up against a limit imposed by your operating system on the per-process number of open file descriptors. Many operating systems permit you to increase the open-files limit, although the method varies widely from system to system.

In detail, this is explained here

http://dev.mysql.com/doc/refman/5.5/en/table-cache.html

EDIT

To verify your assumption you could decrease max_connections and table_open_cache temporarily by SET GLOBAL table_open_cache := newValue.

The value can be adjusted dynamically without a server restart.

Prior MySQL 5.1 this variable is called table_cache

What I was trying to tell, is, that decreasing this value will probably even have a negative impact on performance in terms of less possible concurrent reads (queue get’s longer), instead you should try to increase the OS limit and increase max_open_files, but maybe I just don’t see the point here