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TOPIC: 50 "Session Expired" Errors at the Same Time - Any Ideas?

50 "Session Expired" Errors at the Same Time - Any Ideas? 2 years 7 months ago #77799

  • KingKorn
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Hello,

we are using LimeSurvey 1.91+ (build 12416) and the survey in question has a total of 309 variables. What happened is that when we did the survey with 50 participants on 50 different PCs at the same time from the same PC lab, all of their sessions expired at the same time (showing the "session expired" error page when clicking on next). To clarify: The "sessions expired" errors happened roughly at the same time, about half an hour into the survey, not when answering the same question (some participants were one question group ahead of the others and answering one of the question groups took about 2 to 8 minutes). A few hours before that, 50 different participants had succesfully completed the same survey on the same machines. Do you have any idea how this can happen?

The error could not be reproduced in controlled settings. What we tried was this (while a survey was being taken on a client):

1) Restarting the web server and/or the mysql service on the server -> had no effect and LimeSurvey still continued to run and save date. If data was sent from the client to the server while the service was down, the regular error messages (can't contact web server/database) were shown).
2) Changing the clients IP address -> as the PC lab used a single router to the internet with NAT, we thought this could have an impact, too. It had not.
3) Changing the time on the client or the server -> which had no effect on a running survey.
4) Deleting all cookies and temporary internet data etc. on the client's browser, while taking the survey -> which also had no effect and the survey could still be continued (though the active cookies and data shouldn't be deleted anyway).

We also contacted IT and there was no indication that the server or services necessary for the web page to run were interrupted. Following other bug reports (like bugs.limesurvey.org/view.php?id=4970 or bugs.limesurvey.org/view.php?id=5173) we also checked our version (which is fine) and our PHP settings (which seem to be fine, too, e.g. register_globals is off and we don't use any security mods like SUHOSIN etc.).

All in all, I am amazed how robust against all these possible hazards LimeSurvey actually is (like the web server restarting etc.). And the more I think about this, I'm guessing that a global server error or misconfiguration is the source of the problem - but where should we look? Which PHP configuration settings for example could cause 50 (nearly simultaneously started) sessions to expire at the same time?

Or am I missing something fundamental? :D

What PHP settings could cause this? Could the Internet Explorer version used be responsible? But how could 50 sessions expire simultaneously?

Thanks and best regards, MK
Last Edit: 2 years 7 months ago by KingKorn.
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Re: 50 "Session Expired" Errors at the Same Time - Any Ideas? 2 years 7 months ago #77801

  • titoun31
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Hi KingKorn,

Do you previously use LS in your Lab and do you have any same pb?

Check inside your config-default.php at the line 104 the session time : by default :
// $sessionlifetime sets how long until a survey session expires in seconds
$sessionlifetime = 3600;

So put 36000 for example and check your phpinfo.ini of the webserver config and check the session.gc_maxlifetime. If necessary, increase it too.
Otherwise, change inside the config-default.php at the line 107 file by db... Maybe it will be better due to proxy which scratch the connexion...

// Generally you don't want to change that unless you are using LimeSurvey on load-balanced servers
$sessionhandler = 'file';

Good luck

Thibault
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Re: 50 "Session Expired" Errors at the Same Time - Any Ideas? 2 years 7 months ago #78371

  • KingKorn
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Thanks, Thibault. I checked the entries and they are the default values and shouldn't be responsible, I guess. The participant's surveys crashed about 20 minutes into the survey with each question group taking only eight minutes at maximum to complete. Thus, the session should be refreshed often enough. (Or am I missing something?)

Any ideas, what could go wrong on the server that could cause 50 surveys to crash simultaneously?

By the way: What does the file/db switch do exactly?
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Re: 50 "Session Expired" Errors at the Same Time - Any Ideas? 2 years 7 months ago #78676

  • Mazi
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This sounds like a server configuration problem. Maybe there is some limit at the number of session at the same time?

Please upload a phpinfo file so we can take a look at your server configuration. Just put the following code into a file named phpinfo.php and upload it to your webserver:
< ?php phpinfo(); ? >
(Delete the spaces next to </> when copying the code.)
After uploading please post the link to the file.

Best regards/Beste Grüße,
Dr. Marcel Minke
(Limesurvey Head of Support)
Need Help? We offer professional Limesurvey support
Contact: marcel.minke(at)limesurvey.org'"
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