** Using WeBWorK **

30,000 ( 200 students * 15 prob. * 10 (l2h generated) pictures per problem)

It have not been a problem up to now, but we are trying to troubleshoot a Webserver problem.

Thanks, Yavor Markov

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Current versions of WeBWorK split the images into subdirectories, so each student (psvn) has its own directory in each problem set. If that is not how your version of WeBWorK is dividing up images, you probably have your problem. It would explain the intermittent nature of the problems, since you are flirting with the limit.

John

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Hopefully someone with "systems" expertise can give Yavor a more specific answer.

Arnie

PS. I see John got his response in before me. It's good to hear from experts.

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I have been running John Jones' dvipng version instead of using latex2html this semester. There have been absolutely no glitches so far (we have a dual 700MHz Xeon CPUs with 1GB RAM Dell server running RedHat 7.0, and about 1000 students). The major advantage is NO MORE PRECREATION! Dvipng is almost as fast as tth.

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On John Jones' note. We run WW 1.7 so images are split in subdirectories by student.

On A. Pizer's note. Definitely something we need to look at. We missed that step 8 in the instalation.

On Bill Ziemer's note. Are you making that version public any time soon?

Thank you again.

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Dvipng generated images is already available to the public for WeBWorK. Here's some basic information. Using dvipng gives a faster way of generating images in typeset mode. If a single problem has a huge number of images, it is actually faster than tth. For a just couple of images in a problem (which is more typical), it is slower than tth, but still managable.

Dvipng mode will leave its images on the disk and reuse them if they are there. So, the first time a problem is rendered WeBWorK generates the images. Hitting the submit button does need to create them again.

For our system, I have a daily cron job which deletes everything which has not been accessed recently in CourseNames/html/tmp/*, including images produced by dvipng. If a student works on a problem one day, and then comes back 2 days later, we end up regenerating the images. With more students, we might want to clean less frequently, or use a different parameter for "accessed recently" above (I use 20 minutes).

Implimenting this for your system takes two things: replacing relevant WeBWorK files and adding the additional software. The WeBWorK files are all in the Rochester CVS. At this point, I would advise get a whole new set for installation. Dvipng mode is not the only change since 1.7 and changes in one file may require a newer version of another file.

The extra software can be installed separately. It consists of "dvipng" itself, which takes a dvi file and converts each page into a png image, and "preview", which is a latex package that can be used to produce the special dvi file (with one formula per page, and with page sizes cropped tightly to the formulas).

I would recommend installing dvipng/preview first since it will not interfere with current system operation. Depending on how similar your system is to mine, this could take as little as a few minutes (or as long as, well, don't ask). Ultimately, we will have a better installation process. You can download it from

http://hobbes.la.asu.edu/webwork-stuff

It is near the top of the page.

Let me know about successes/difficulties in installing the parts from my page.

John

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Arnie

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