** Using WeBWorK **

Normally I would suggest restarting the apache server, since a runaway child process can cause this kind of behavior. In this case that seems unlikely since it is only creating the images that is slow, but you should try that anywayif you haven't already.

It's possible to set up WeBWorK so that the images are served through lighttpd (a light weight server). Again I don't that is the problem but you should check how you are serving static images in any case. This will be the case if you are serving images on port 8080 or 8000. See release notes for recent WeBWorKs for details.

Having said all of that this will be difficult to debug from distance. Here is what I can tell you.


The mechanism that creates the link to the alias files is in pg/lib/PGalias.pm.
Most of this code seems straightforward and wouldn't cause a slowdown, but there is one place where PGalias checks to see if the link was actually created properly by issuing a curl or lwp-request command to ping the newly created link. That could be failing and causing a slowdown.

The actual command line for this is in site.conf where I have:

####################################################
# url checker
####################################################
# set timeout time (-t 40 sec) to be less than timeout for problem (usually 60 seconds)
$externalPrograms{checkurl} = "/usr/bin/curl -I"; #or "/usr/bin/lwp-request -d -t 40 -mHEAD "; # or "/usr/local/bin/w3c -head "
$externalPrograms{curlCommand} = "/usr/bin/curl";

#FIXME there was an error using lwp-request ??? you get:
# [mgage@its-webwork-up03.its.rochester.edu]$ /usr/bin/lwp-request -d -t 40 -mHEAD
# https://math.webwork.rochester.edu/webwork2_files/applets/geogebra_stable/geogebra.jar
# 501 Protocol scheme 'https' is not supported (IO::Socket::SSL not installed)
# and you get this even after running cpan to install IO::Socket::SSL --
# which is installed at Installing /opt/rh/perl516/root/usr/local/share/perl5/IO/Socket/SSL.pm

You can see that on my site there was some trouble with lwp-request and I switched over to curl. You can see also that when you use lwp-request there is a timeout if the ping fails. (Nothing is set using curl -- which is probably dangerous -- I'll have to go back to fix this. )

I wonder if that is what is happening on your machine. Something in the behavior of lwp-request and curl could easily have changed during a system upgrade.

Let us know what you find out.

-- Mike

THANKS!!! That fixed it, for some reason lwp-request for a local url doesn't work for a link that is local to the server but does if we test an external url:

Three examples:
1) checking link on the server using lwp-request on the server:

/usr/bin/lwp-request -d -t 40 -mHEAD https://webwork.math.montana.edu/wwtmp/S18M171//gif/6f220643-a8b4-333a-8fe7-96607065a064___3cd22e5e-bc29-3de2-a440-15f4fd36c705.pngwww.monta
500 Can't connect to webwork.math.montana.edu:443

2) checking an external link using lwp-request on the server
/usr/bin/lwp-request -d -t 40 -mHEAD www.montana.edu
200 OK

3) checking the link on the server using lwp-request on another 16.04 box:
/usr/bin/lwp-request -d -t 40 -mHEAD "https://webwork.math.montana.edu/wwtmp/S18M171//gif/6f220643-a8b4-333a-8fe7-96607065a064___3cd22e5e-bc29-3de2-a440-15f4fd36c705.png"
200 OK

It seems that the dynamic images are not checked for a valid url but the static ones are. If we comment out the check in PGalias and retrun 1 as Michael suggests everything seems to be back to normal.

THANKS we have had a lot of very up happy calculus students learning to be patience.

Another question: why would you want to check to see if the url is valid?

Thanks Again!