MySQL server has gone away

[benoitchantre]

Since the upgrade to WP 4.5, I can see many warnings like this in the logs.
I use Comet Cache Pro (static cache) and the warnings disappear when I disable it.

I have have contacted my host and the answer is the warning appears, because the connexion with mySQL has timed out because of inactivity.

[Mon May 16 23:49:54 2016] [error] [client 128.65.195.34] FastCGI: server "/home/clients/b9bea0796c13d5f0e5012c76b5730384/.config/apache/mydomain.com/.fpm/php5.external" stderr: PHP message: PHP Warning: mysqli_query(): MySQL server has gone away in /home/clients/b9bea0796c13d5f0e5012c76b5730384/web/_wp/wp-includes/wp-db.php on line 1811

[Tue May 17 22:23:51 2016] [error] [client 128.65.195.34] FastCGI: server "/home/clients/b9bea0796c13d5f0e5012c76b5730384/.config/apache/mydomain.com/.fpm/php5.external" stderr: PHP message: PHP Warning: mysqli_query(): Error reading result set's header in /home/clients/b9bea0796c13d5f0e5012c76b5730384/web/_wp/wp-includes/wp-db.php on line 1811

Many other user have reported issues like this with other plugins

• ​https://wordpress.org/support/topic/upgrade-to-wp-45-error-with-wordfence
• ​https://wordpress.org/support/topic/wordpress-452-issues

Is it a bug introduced in WP 4.5?

[raamdev]

There's a bit more discussion about this here: ​https://github.com/websharks/comet-cache/issues/758#issuecomment-219849555

[lukecavanagh]

So this does seem more like an issue with Comet Cache than being directly related to WordPress core.

[pento]

It looks like this particular problem was caused by a slow process in Comet Cache.

WordPress tries to regain the MySQL connection if it goes away mid page load, but you'll still see this error in your error log.