Hello,

I upgraded our LimeSurvey install from 3.12 to the latest version 3.25.12+210211 using ComfortUpdate, which went perfectly fine. Everything seems to be working correctly, except that submitting surveys no longer works. When hitting the submit button on any survey (even a newly created test survey with a single question), the page becomes unresponsive for a few minutes, then comes up with "CDbException: CDbCommand failed to execute the SQL statement: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away."

When checking the database with PhpMyAdmin, it appears that the response is actually recorded. However, LimeSurvey still hangs, no admin emails are sent, and obviously no 'end page' comes up. Creating the new survey also works fine, and correctly adds everything to the database, so it does seem that the LimeSurvey install is corresponding with MySQL just fine - except at some point after the submission of a survey, I guess.

Switching on debug mode in the config.php leads to a PHP warning that max_time_limit() has been disabled due to security reasons. It's on a shared hosting account, so I don't think there is much that I can alter there; the previous 3.12 version was working just fine, so I also don't see why there should be an issue there. That warning disallows me from accessing LimeSurvey any further, so there's little additional info I seem to be able to get through there.

LimeSurvey is running on a server with PHP 7.4 and MySQL 5.7. 

We urgently need the system up and running, so I'd be appreciative of any ideas. Otherwise I'd have to try downgrading back to the backed up 3.12 version, which I would rather not do.

I think I have managed to track down the issue. If I am correct, it is not an issue with LimeSurvey or the upgrade.

It turns out that a short while before I performed the upgrade, there was some change in infrastructure, and our LimeSurvey installation ended up on a server with a different IP address. Our installation is set up to connect to our email server via SMTP to send its emails, but that only accepts requests from authorised addresses.

The whitelisted address in the configuration is still the old one, not the new one. That means LimeSurvey ended up waiting for a response from the email server, which never came, finally resulting in a timeout with the error above – it's a little misleading because it seems to suggest an issue with the database.

It must have already broken before I performed the update, but we did not notice it as we had no active surveys running. A somewhat rare moment, which is also what I made use of to do the update in the first place.

Just waiting for our IT to whitelist the new address, and hopefully things should work normally again.

Great to have more information


The error CDbException: CDbCommand failed to execute the SQL statement: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away.
still really strange