Magento MySQL Has Gone Away Error

This is mostly due to any of the below two reasons

1. Server timed out and closed the connection.
   fix: try increasing the wait_timeout variable in your mysqld’s my.cnf/my.ini configuration file.
2. Server dropped an incorrect or too large packet.
   fix : increase the maximal packet size limit by increasing the value of max_allowed_packet in my.cnf/my.ini file.

Please check in files if you are trying to get something that is taking too long or inapplicable.

Issue resolved! Thanks to all for the help. This was a hardware firewall issue with the web host, even after they were disabled by us.

As confirmed by 1&1's server team, the hardware firewalls were correctly configured, but they were incorrectly intercepting valid traffic between the file server and the db server about 25% of the time.

We have configured iptables instead and shutdown the hardware firewalls entirely. 100% availability now.

I experienced the same issue for Magento 2.1 and my mysql error log showed the following error multiple times during the "MySQL has gone away" process:

...[Warning] File Descriptor 1228 exceeded FD_SETSIZE=1024

To potentially resolve this issue, firstly check the open files value with $ ulimit -n, which in my case was 256.

Secondly, add table_open_cache = {that ulimit -n value} under the [mysqld] section in your my.cnf.

Now restart MySQL and hopefully you're back into the action.

Note: I'm running Magento 2.1 locally on OS X El Capitan with PHP 7.1 and MySQL 5.7.15 build with Homebrew. But I bet this solution would work on older or different setups too.