Sudden “MySQL server has gone away” error in PHP site

Question

Today one of my websites started showing

Error Number: 2006
MySQL server has gone away

It\'s a low-traffic client site running under Apache 2.2.9 (Debian

Answer 1

It's probably a connection time out affecting your persistent connections in PHP. I used to see them all of the time. The timeout parameter is within MySQL itself.

Your options include: - not using persistent connections - turning off idle timeout on the MySQL server - trapping the error

I always wrap reconnection into my own PDO class, so I can't even remember if PHP reconnects or not. In any case, it's an easy fix. On query, catch & reconnect.

I have "generated" this error in the past with InnoDB. If you're using that engine, what's the output of SHOW ENGINE INNODB STATUS after a failure?

Answer 2

Since the other sites work, we can assume that it is related to your site (and not the server). The official documents mention that this might happen if you try to execute queries after the server connection is closed. Do you have any hooks in CodeIgniter that does something towards the end of a request where the database connection might be closed?

Answer 3

As I said in my update, I concluded that the problem with MySQL arises when the link to Facebook takes longer than the maximum connection time with the DB. None of the suggestions could beat this limitation, so I decided to work around it and reconnect every time I presumed the link maybe gone.

So after each call to Facebook, I used to following code:

$this->load->database();
$this->db->reconnect();

This is the particular solution when using CodeIgniter, and AFAIK the db->reconnect() function is only available since version 1.7.2 so I updated it in order to work.

Thanks everyone for your answers!

Answer 4

You mention that this is an overnight task and that you're getting FaceBook data etc. Is the process running for a long time?

I've had a recent script that is moving data from one cluster to another and transforming formats etc. This script runs 24/7 moving this data across. I've found that with or without persistent connections, the MySQL libraries will still drop out after a few minutes (sometimes 5 minutes, sometimes longer).

The only way I've found to get around it for my case was to put a time check in my wrapper and to check how long it's been since the last time I reconnected before executing the query. I've set it to check if it's been greater than 2 minutes and if so, to reestablish the connection, ensuring to set the "new_link" flag (4th param) on mysql_connect is set to false.

Since changing this, I've never had the same error again.