MySQL file limit, table cache and max_connections

MySQL variables open_files_limit, table_open_cache and max_connections are
inter-related, and this is for obvious reasons: all deal with file descriptors
one way or another.

If one of the value is provided but others are left out, mysqld calculates
others using a formula and in some cases, emits a warning if not possible.

The whole calculation behind obtaining the final file descriptor limit is a bit
byzantine and is as follows (for Linux):

EDIT: This applies to MySQL 5.5, in 5.6, as Daniël in comments pointed out,
few things have changed, check comment for details. I will probably make a
followup post on the differences.

  1. First it tries to calculate a minimum requirement based on max_connections
    and table_open_cache. As for other variables, if it is not provided in cnf or
    on command line it uses defaults.

    <br />    /* MyISAM requires two file handles per table. */
        wanted_files= 10+max_connections+table_cache_size*2;
    

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