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Response time- server issues?

Response time- server issues?

by Joel Trussell -
Number of replies: 5
I write and maintain the Webwork problem codes and help the ECE faculty with their classes. I don't maintain the Webwork server or software. There have been several problems this semester that seem to me to be server related, e.g.,
1) The response time for Webwork at the time near the due date/time makes it difficult for students to submit on time
2) students taking an in-class test suffered delays that required extending the time beyond the class period.
3) faculty making assignments to problem set due dates/times are being logged out after every change - they have to go back to the login for each change - I've had similar log out occur when updating assignments, but in the lab sections this is very inconvenient since it has to be done a great many times.
4) Following the link from an email sent from the "Email the instuctor" button, logs me on as myself, not acting as the student. I have to kill the browser page and click on the link in the email again. The second time I'm logged in as acting as the student and can see the answers submitted.

Questions: Are these really servers problems? could code problem cause the delay when we've used these same test questions in previous semesters? (that is one of the advantages of Webwork, the same problem appears different for each student). Any advice or hints?

thanks

In reply to Joel Trussell

Re: Response time- server issues?

by Jeremy Lounds -
Hello Joel,

I can weigh in on our experience with performance related issues. (We are running 2.13 in production right now, and testing 2.14) WeBWorK appears to have a memory leak somewhere, so it is important to dial-in the correct settings for Apache MPM Prefork. The correct settings for your server(s) will vary on the amount of RAM you have available, and the number of simultaneous users.

There is a mention in the install guide, and more info in the forum here on how this all works together.


Here is a general site on Apache MP Prefork that you may find helpful as well


Another key setting for us was turning off KeepAlive, but this recommendation may not apply to you, depending on how your firewall and network is designed.
In reply to Jeremy Lounds

Re: Response time- server issues?

by Michael Gage -
In general we recommend restarting the server every 24 hours to help with the memory leak. It's not huge (more research will be required to locate it (or them) its probably in some pg problems. You can safely restart a server at some low traffic time such as 4am using "apachectl graceful" At the worst it causes a one second delay or so in responding to a student problem.
In reply to Michael Gage

Re: Response time- server issues?

by Michael Gage -
I also recommend setting due dates at 4am in the morning. It reduces the natural impulse for all students to submit minutes before the deadline.

For large in class exams I think that you just need more memory and/or faster machines.
In reply to Michael Gage

Re: Response time- server issues?

by Danny Glin -
For large in-class exams having the correct apache prefork settings can help, but even the optimal settings will only be as effective as the available system resources. This means more RAM and possibly more processor cores. Based on my experience the speed of the processor(s) is less important than the number of cores since the slowdown is usually caused by a large number of small tasks rather than one or two big ones.

Regarding your problems with getting logged out, I have a couple of thoughts:
What version of WeBWorK are you running? Sometimes bugs have already been fixed in the latest version.
Based on your points 3 and 4 it sounds like this might have something to do with your authentication mechanism. Are you using an integration with your institution's login? If so, it's possible that there is some weirdness going on with session keys/cookies. If you are using internal WeBWorK usernames and passwords, then it's possible that there is something going on with multiple sessions (i.e. a user logging in more than once). Do your instructors share accounts?
In reply to Danny Glin

Re: Response time- server issues?

by Joel Trussell -
I can't say anything about the RAM and cores.
I can say that there were some labs that had the same number of students that did not experience delays and all when well. I have not looked at the times of those labs.

Log out problem - we are running WW ver 2-13, PG ver 2-13
All classes use integrated with the NCSU login.