Random problem connecting to MySQL

Posted by CharlesLeaf on Stack Overflow See other posts from Stack Overflow or by CharlesLeaf
Published on 2010-05-26T08:46:51Z Indexed on 2010/05/26 8:51 UTC
Read the original article Hit count: 192

Filed under:

mysql

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php5

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random

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connection

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problem

Environment:
RHEL 5 servers, MySQL 5.1.43, PHP 5.1.6 (using MySQLi).
Currently only available within our internal VPN network.

Servers
ServerA: Webserver
ServerB/C/D: Database server (1 master 2 slaves)

The error (on ServerA)
[Tue May 25 11:12:17 2010] [error] [client CLIENTIP] PHP Warning: mysqli::real_connect() [function.mysqli-real-connect]: (HY000/2003): Can't connect to MySQL server on 'ServerB' (4) in /home/**/Database.php on line 67, referer: [website]

Problem description
It appears that at completely random times, our website is unable to connect to one of the MySQL servers - usually the Master. Except for the forementioned error message, there is nothing to be found in any of the logs as far as I can see, and most of the times the connection is succesful and everything works as it should. It's just at completely random times, this error pops up.

There's no firewall blocking any internal traffic, timeout value is 3 but it doesn't take 3 seconds before it fails to connect. With the default mysql client I can connect from ServerA to ServerB,C and D and haven't encountered a problem yet.

Does anyone have a clue what I might be overlooking / could be the problem? Because I've run out of ideas myself.

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