Question

I have a Master – Slave setup for a web application written in PHP. I have a pool of slaves I use for reading, and a Master that is used for writes (and reads if a write has been sent this request). I would like to incorporate an automated system for removed crashed servers from the read pool. Currently I am using:

foreach($readers as $reader)
    {

        $fp = @fsockopen($reader['host'],3306,$errno,$errstr,1);
        if(!$fp)
        {
            //Remove from pool
        }
        unset($fp);
    }

My primary question is there a more reliable method. I have had quite a few false positives, and vice versa because it is not actually checking for a MySQL server, but rather just a connection on port 3306. Is there a way to check for a MySQL server without raising an exception, which is the behaviour of the PDO and MySQLi extensions in PHP.

Answer 1

You could just use mysql_connect() and check the result for false, and close the connection right away on success. You can make a dummy account with no privileges for that if you like.

That’s really the only reliable way, especially if you want to distinguish a running MySQL server from any other random process listening on port 3306.