UsingWW: Jun Wang - Homework assignment error, what is the probable cause?

$inactiveTopic$ Homework assignment error, what is the probable cause?

topic started 9/12/2006; 6:49:21 PM
last post 9/14/2006; 1:41:25 PM

$user$ Jun Wang - Homework assignment error, what is the probable cause? $blueArrow$
9/12/2006; 6:49:21 PM (reads: 290, responses: 8)

We recently are experiencing one type of trouble with our system:

Sometimes (not always) when a teacher assigns a homework set to ALL users, the system takes a long time and does not finish it. One time we left it running for one hour and it did not finish. If we stop the task, the database course_set_user or course_problem_user would be damaged. It also happened a couple of times when a teacher was adding problems to a homework set (the system could finish adding all the problem to the set). It occurs to multiple courses. So far we have been able to use the "REPAIR TABLE" to fix the database, but the problem is happening very often and it is very frustrating.

Our administrator said it could be something wrong with the file system on the hard drive of the server. Before we check that, is there any other probable cause for this type of behavior? Thanks,

Jun

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$user$ Michael Gage - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/12/2006; 9:03:59 PM (reads: 321, responses: 0)

Hi Jun,

I don't think we've seen anything like this in quite awhile. What version of WeBWorK are you running? How big are the classes? and homework set size? Can you run "top" to get an idea of how big a load there is on the machine? Also are there problems with free disk space?

Even if the browser times out the task is supposed to finish. (For example when I assigned email it would take a long time because our smtp server was a bit slow -- so I would just quit the browser -- but the email would be sent even though I didn't get the final message about success.)

-- Mike

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$user$ Jun Wang - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/12/2006; 11:18:15 PM (reads: 327, responses: 0)

Hi, Mike,

Our version is WeBWorK 2.2.2, just upgraded last month. But the problem existed before that, with version 2.1. It just got worse since the summer. It happened even to very small classes. Just last week I was assigning a homework set of 11 problems to a graduate course with only 4 students. After about one hour, it assigned successfully to 3 students and assigned the 4th students 7 out 11 questions only. The table MAT622_problem_user was damaged and I could not unassign this student either. After fixing the table, I was able to assign the set to one or two students at a time. There were enough free disk space but I did not check the load. Tomorrow I will see if I can reprodce this problem and check the load.

Jun

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$user$ Michael Gage - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/12/2006; 11:47:23 PM (reads: 323, responses: 0)

This doesn't sound like anything we're seeing on our installations here, or that I've heard about. I don't think it's a load problem -- something is certainly not functioning properly. The delays could be either bad connections, (with long timeouts waiting to try again) or some kind of closed loop. I'd be prepared to think it was a hardware or underlying systems problem (as suggested by your administrator) but I'm not an expert in these matters. It might be affecting mysql and that in turn is affecting WeBWorK. There is very little if any direct disk storage in assigning problems -- it's all interaction with the database.

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$user$ Michael Gage - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/12/2006; 11:49:24 PM (reads: 320, responses: 0)

one thing -- use mysqldump to backup the database before you start fiddling with it. You don't want to loose your data from the beginning of the semester.

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$user$ Arnold K. Pizer - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/13/2006; 11:03:21 AM (reads: 312, responses: 0)

It's a long shot, but what happens if you stop and then restart mysql (and apache for good measure).

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$user$ Jun Wang - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/13/2006; 11:59:29 AM (reads: 319, responses: 0)

Hi, Arnie,

We stopped and restarted mysql, then one of the tables would be labeled as damaged "code 145". Using "REPAIR TABLE" we could fix the table and everything would be like what they were before.

Our Administrator is going to back up the database and run "mount" and fix the file system on the hard drive now.

Jun

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$user$ Jun Wang - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/13/2006; 7:08:25 PM (reads: 313, responses: 0)

We check the file system and in the process corrected a lot of damaged tmp files (created by webwork, I guess). It seems now that the problem indeed was due to the hardware. We hope this will fix the problem for good, and if not, I will post a follow up.

Jun

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$user$ Gavin LaRose - Re: Homework assignment error, what is the probable cause? $blueArrow$
9/14/2006; 1:41:25 PM (reads: 296, responses: 0)

Hi Jun,

This isn't really a helpful comment, but your mention of the mysql table damage has jogged my memory.

There was a point on our previous server at which I noticed that we were getting sporadic data corruption in the mysql databases. I never tracked down the origin of this, and ended up just sticking a script in cron to go through and check and, if necessary, repair the tables periodically. That was mysql 4.0.16 on Solaris, for what it's worth.

Cheers,
Gavin

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Jun Wang - Homework assignment error, what is the probable cause?

Jun Wang - Homework assignment error, what is the probable cause?