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WeBWorK Main Forum -> WeBWorK Warning Messages When Deleting Courses

by Sherman Wong -

I would like to delete "old" WeBWorK sections, i.e., sections that are at least one year old.  I have been using the "Course Administration" interface to perform this task.  However, recently, each time that I've deleted a section, the program responds with a message that the deletion of the section was successful, but then there is a long list of WeBWorK warnings.  Moreover, when I refresh the page, I get the following error message:

An error occured while deleting the course MTH2003_JM13C_S07:

sql_single: failed to execute SQL statement 'DROP TABLE `MTH2003_JM13C_S07_problem_user`;': Unknown table 'MTH2003_JM13C_S07_problem_user'

I don't wish to damage the database.  I'd appreciate any assistance in the explanation of the error message.  I do have a copy of the long list of warnings if it would be of help.

Thank you.

Sherman Wong

Forum archive 2000-2006 -> James - Apache Memory Problems

by Arnold Pizer -
inactiveTopicApache Memory Problems topic started 12/3/2006; 9:46:01 PM
last post 12/12/2006; 11:07:42 PM
userJames - Apache Memory Problems  blueArrow
12/3/2006; 9:46:01 PM (reads: 358, responses: 3)
Greetings all,

Brian Camp and I have set up a webwork server using Webwork 2.3 ( patched branch ). We use Apache 2.0.54, Perl 5.8.6, on Fedora Core 4.

We have been having issues with Apache and Memory.

Our server is dual processor, dual core Xeons, with 1GB RAM and 3.5GB swap.

On two occasions we have checked the server and found apache misbehaving.

Saturday, an instructor called saying WW was not working. We checked into it, and apache had used all available RAM, as well as all available swap. The professor had been using Course administration to select problems for a homework set. He had selected 'show all' from the drop down, so he was trying to view all 500 problems in the library. Apparently the server had not responded so he tried again and again until he contacted us. When we checked apache was using all available RAM as well as nearly all available swap. We restarted apache. And then I followed the advice in the below threads:

http://webhost.math.rochester.edu/webworkdocs/discuss/msgReader$3168#3189 http://webhost.math.rochester.edu/webworkdocs/discuss/msgReader$4481

I changed our httpd.conf to: 

KeepAlive On



MaxKeepAliveRequests 10



KeepAliveTimeout 15



<IfModule prefork.c>
StartServers 8
MinSpareServers 5
MaxSpareServers 20
ServerLimit 70
MaxClients 160
MaxRequestsPerChild 100
</IfModule>



<IfModule worker.c>
StartServers 2
MaxClients 150
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25
MaxRequestsPerChild 100
</IfModule>



PerlSetEnv PERL_RLIMIT_AS 100:120
PerlModule Apache2::Resource

Today ( Sunday ) our server became unusable. After logging in to the server we restarted apache again. It was using all available RAM, and was using about half available swap.

Looking through the apache error log, we were able to identify when the problem started, and from that point on the logs are littered with: [Sun Dec 03 18:39:01 2006] [info] (104)Connection reset by peer: core_output_filter: writing data to the network [Sun Dec 03 18:39:02 2006] [info] (32)Broken pipe: core_output_filter: writing data to the network [Sun Dec 03 18:39:02 2006] [info] server seems busy, (you may need to increase StartServers, or Min/MaxSpareServers), spawning 16 children, there are 0 idle, and 42 total children

We then checked the webwork logs and found one user had managed to submit an answer to a problem 405 times in about 2 minutes. We tried recreating the error by logging in and doing the same problem, with the answer they submited but never caused the server to go crazy.

Any idea what might be the problem? Any recommendations on apache configuration?

Thanks for your time,

James Elliott & Brian Camp

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userMichael Gage - Re: Apache Memory Problems  blueArrow
12/3/2006; 10:34:53 PM (reads: 404, responses: 0)
I would put the max clients down to around 20. We keep it at 10 on hosted, but we only have 500 Meg of memory for that machine.

 

Timeout 1200
KeepAlive On
#MaxKeepAliveRequests 100
MaxKeepAliveRequests 50
KeepAliveTimeout 10
StartServers 5
MinSpareServers 5  
MaxSpareServers 10
#sam# Default is 150, but was previously set to 10. Trying 50 for now to
#sam# see if there'll be any problems.
#mike# there were some problems -- trying 25 clients -- (see Oct 22, 2006)-- some problems timed out
#Mike# still problems -- reducing it to 15
#mike# now to 10
MaxClients 10
MaxRequestsPerChild 300

As you can see some experimentation is necessary. A webwork child takes about 50Meg of memory, and it appears that it works best if you keep the total amount of memory that can be claimed by the children to less than the physical RAM available.

Hope this helps.

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userBrian Camp - Re: Apache Memory Problems  blueArrow
12/3/2006; 11:54:03 PM (reads: 406, responses: 0)
Mike,

Thanks for the quick response!

I had another apache question that I think is related to this. What sorts of modules should apache be loaded with? For example, have you tinkered with this on hosted or hosted2 to try and make your server more efficient for webwork?

Here are the modules that we currently are loading: 

> LoadModule access_module modules/mod_access.so
> LoadModule auth_module modules/mod_auth.so
> LoadModule auth_anon_module modules/mod_auth_anon.so
> LoadModule auth_dbm_module modules/mod_auth_dbm.so
> LoadModule auth_digest_module modules/mod_auth_digest.so
> LoadModule ldap_module modules/mod_ldap.so
> LoadModule auth_ldap_module modules/mod_auth_ldap.so
> LoadModule include_module modules/mod_include.so
> LoadModule log_config_module modules/mod_log_config.so
> LoadModule logio_module modules/mod_logio.so
> LoadModule env_module modules/mod_env.so
> LoadModule mime_magic_module modules/mod_mime_magic.so
> LoadModule cern_meta_module modules/mod_cern_meta.so
> LoadModule expires_module modules/mod_expires.so
> LoadModule deflate_module modules/mod_deflate.so
> LoadModule headers_module modules/mod_headers.so
> LoadModule usertrack_module modules/mod_usertrack.so
> LoadModule setenvif_module modules/mod_setenvif.so
> LoadModule mime_module modules/mod_mime.so
> LoadModule dav_module modules/mod_dav.so
> LoadModule status_module modules/mod_status.so
> LoadModule autoindex_module modules/mod_autoindex.so
> LoadModule asis_module modules/mod_asis.so
> LoadModule info_module modules/mod_info.so
> LoadModule dav_fs_module modules/mod_dav_fs.so
> LoadModule vhost_alias_module modules/mod_vhost_alias.so
> LoadModule negotiation_module modules/mod_negotiation.so
> LoadModule dir_module modules/mod_dir.so
> LoadModule actions_module modules/mod_actions.so
> LoadModule speling_module modules/mod_speling.so
> LoadModule userdir_module modules/mod_userdir.so
> LoadModule alias_module modules/mod_alias.so
> LoadModule rewrite_module modules/mod_rewrite.so
> LoadModule proxy_module modules/mod_proxy.so
> LoadModule proxy_ftp_module modules/mod_proxy_ftp.so
> LoadModule proxy_http_module modules/mod_proxy_http.so
> LoadModule proxy_connect_module modules/mod_proxy_connect.so
> LoadModule cache_module modules/mod_cache.so
> LoadModule suexec_module modules/mod_suexec.so
> LoadModule disk_cache_module modules/mod_disk_cache.so
> LoadModule file_cache_module modules/mod_file_cache.so
> LoadModule mem_cache_module modules/mod_mem_cache.so
> LoadModule cgi_module modules/mod_cgi.so
Also, we decided to keep temporary copies of images generated by webwork on the fly. Do you have any suggestions on how long images should be kept for? For example, do you run a nightly cron job to delete images that are stale (i.e. perhaps older than x hours or x days)? Is there even a way to do this?

Initially we had not been storing images generated on the fly so that they would have to be regenerated. I think this may have led to our difficulty with the instructor browsing the problem library.

They had picked something like 518 problems they wanted to view. Images was their default display option. This by itself was not a problem but then they would then click on something else causing the page to want to redraw all 518 problems. Is this a bug in the problem library? It would seem that there might be a better way to select libraries and problem sets and so on without the display needing to refresh every time a button is clicked. On the other hand, I am trying to discourage the instructor from having to view such massive numbers of problems all at the same time :)

Thanks again for all of the help, Brian

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userWilliam Wheeler - Re: Apache Memory Problems  blueArrow
12/12/2006; 11:07:42 PM (reads: 315, responses: 0)
Dear James and Brian,

Re: >We then checked the webwork logs and found one user had managed to submit an answer to a problem 405 times in about 2 minutes. We tried recreating the error by logging in and doing the same problem, with the answer they submited but never caused the server to go crazy.

I see this situation several times each semester. This is an inadvertent Denial of Service (DoS) attack caused by a "bug" in the operating system and browser combination on the computer the student is using. What seems to be the case is that the "Submit" button/mouse combination and/or the "Enter" key act as "repeating" keys, like the letter keys on the keyboard. (Hold down a letter key and watch how fast it repeats.) So if the student holds down the mouse button while the mouse pointer is on the Submit key or holds down the "Enter" key, then the browser will repeatedly submit the form as rapidly as possible. I've seen submission rates approaching 20 submissions per second. I've seen these attacks with both "GET" and "POST" requests.

Each resubmission breaks the computer's network connection to the Apache server. That's the source of the "Connection reset" and "Broken pipe" messages.

These attacks rapidly overwhelm Apache, because it has to assign each request to a new child or an old one that isn't otherwise assigned. (Note: When a connection is broken, it doesn't stop the WeBWorK process that is running; that process will run to completion, at which point the Apache child tries to send the WeBWorK output back to the student's computer; but the child discovers that the "pipe" is broken when it tries to write to the pipe.) Because the rate of submissions is faster than WeBWorK can process the submissions, WeBWorK falls behind and Apache has to create one new child after another. If the attack lasts several minutes, then Apache will overflow both RAM and Swap. The server will appear to be non-responsive, because it is spending almost all of its CPU cycles swapping.

If left alone for a long time, the server will eventually recover on its own. But that may take hours. So the timely response is to stop and restart Apache. (This may take several minutes.)

These inadvertent DoS attacks were a frequent problem with the old Windows Millenium version of Windows. I see the problem less frequently now. Last month I saw one attack from a Mac and one attack from a Windows PC.

I've never been able to recreate this phenomenon on my workstations. But I've spoken with students who were sources of attacks. They usually describe the computer's screen as appearing to "shake rapidly". I usually caution the students to stop using the computers that generated the attacks.

Sincerely,

Bill Wheeler, Indiana University, Bloomington

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Forum archive 2000-2006 -> Lars Jensen - Gateway testing - where?

by Arnold Pizer -
inactiveTopicGateway testing - where? topic started 5/31/2006; 4:10:43 PM
last post 6/7/2006; 9:03:09 PM
userLars Jensen - Gateway testing - where?  blueArrow
5/31/2006; 4:10:43 PM (reads: 1157, responses: 24)
It was my understanding that gateway testing was included in ww 2.2, however, I can't find it. I recall a drop-down menu somewhere in Gavin's preliminary "gateway version" of ww 2.1, that would allow me to configure a problem set for "gateway testing" or "proctored gateway testing," but I can't find it anywhere. Has gateway testing been included in ww 2.2?

Lars.

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userMichael Gage - Re: Gateway testing - where?  blueArrow
5/31/2006; 4:27:17 PM (reads: 1243, responses: 0)
Look towards the top of the Set detail page -- the one on which you edit the contents of a homework set, assign weights to problems, due dates and so forth. There is a pop-up button for assignment type that allows you to select either homework or gateway

-- Mike

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userLars Jensen - Re: Gateway testing - where?  blueArrow
5/31/2006; 5:02:16 PM (reads: 1239, responses: 0)
Thanks Mike!

<| Post or View Comments |>

userLars Jensen - Re: Gateway testing - where?  blueArrow
5/31/2006; 5:10:58 PM (reads: 1236, responses: 0)
Hi Mike,

Just tried to change the "Assignment type" setting of a problem set, and it turns out that it can't be changed - the only setting that "sticks" is "homework." No matter what I choose from the drop-down menu, once I click the "Save changes" button, the setting returns to "homework."

Lars.

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userMichael Gage - Re: Gateway testing - where?  blueArrow
5/31/2006; 5:58:48 PM (reads: 1252, responses: 0)
I haven't been able to reproduce this.

I took an existing homework course. Changed homework to gateway/quiz. Pressed "Save Changes" at the top of the page.

The return page had extra blanks to fill in regarding the parameters for the quiz.

Gavin LaRose is the principal author on this module, we might have to consult him.

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userLars Jensen - Re: Gateway testing - where?  blueArrow
5/31/2006; 7:13:08 PM (reads: 1246, responses: 0)
Hi Mike,

That's what I did as well, except that the "gateway/quiz" setting switched back to "homework" instantly as I clicked "Save changes."

You are running development 2.2, though, right? I'm running plain 2.2.

Lars.

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userGavin LaRose - Re: Gateway testing - where?  blueArrow
6/1/2006; 9:31:27 AM (reads: 1234, responses: 1)
Hi Lars,

I've never seen this problem, but I'm running versions of WeBWorK that are well behind the curve. It sounds as if either the assignment type isn't being saved to the mySQL database, or the set detail page is automatically giving the default answer rather than what's in the database. Do you have access to the mySQL database? The easiest thing to do would be to check the actual assignment type in the database to see if it's correct.

Gavin

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userLars Jensen - Re: Gateway testing - where?  blueArrow
6/1/2006; 10:34:26 AM (reads: 1341, responses: 0)
Hi Gavin,

Yes, I do have mysql access. And I found the setName_set table with table entry "assignment_type", and it does indeed say "gateway." However when I login to the course and look at the same setting after editing the course in the library browser, it is still listed as "homework" and none of the extra blanks that Mike refered to pops up.

Lars.

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userMichael Gage - Re: Gateway testing - where?  blueArrow
6/1/2006; 1:25:21 PM (reads: 1225, responses: 0)
I'm using version 1.37 of ProblemSetDetail.pm You probably have version 1.32. The differences are cosmetic user interface as far as I can tell, but one of them might be causing your difficulty. You might try selectively updating

cvs status ProblemSetDetail.pm

will give you the version you are currently using.

cvs update -r 1.37 ProblemSetDetail.pm

will update just that one file.

Hope this helps.

-- Mike

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userLars Jensen - Re: Gateway testing - where?  blueArrow
6/1/2006; 2:17:13 PM (reads: 1212, responses: 0)
Hi Mike,

Tried this - it didn't help...

Lars.

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userGavin LaRose - Re: Gateway testing - where?  blueArrow
6/2/2006; 8:46:34 AM (reads: 1209, responses: 0)
Hi Lars,

I'm not sure I completely understand what you're seeing here. I think you've described two apparently buggy behaviours: (1) when you go to the set detail page, select "gateway", and press "save", it returns with the set detail page but the assignment type reset to "homework" (even though the database indicates that the assignment type has been saved as "gateway"), and (2) after resetting the assignment type to "gateway", if you enter the Library browser the assignment type in the database gets reset as "homework". (Please let me know if that description isn't correct.)

I don't understand (1), because I've never seen that behavior (I've only seen the sequence of events that Mike indicated) and unfortunately don't have the time this morning to look at it to try and figure out what's going on. I'll be able to look at it next week, at which point I'll grab the latest version of WeBWorK out of the CVS and see if I can duplicate your problem. (2) might be more understandable; I haven't worked at all with the Library browser, so it may be that it creates/works with assignments without specifying an "assignment_type". I'd expect that this should result in the type not being changed, but I could possibly imagine some way that it might end up resetting the type unexpectedly.

Gavin

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userLars Jensen - Re: Gateway testing - where?  blueArrow
6/3/2006; 2:08:41 PM (reads: 1207, responses: 0)
Hi Gavin,

Your statement (1) above is exactly correct, and contains everything. I'm not sure that (2) adds anything.

So to summarize, here's what's going on:

(i) Enter the library browser

(ii) select a set from the "Select a Set from this Course" drop-down menu and click the "Edit Target Set" button

(iii) Select "gateway/quiz" from the "Assignment type" drop-down menu, and click "Save changes"

After carrying out (iii), (a) the web page instantly refreshes, listing the "Assignment type" as "homework" (on the drop-down menu), and (b) the mysql database correctly changes assignment_type to "gateway."

None of the "blanks" Mike mentions show up on the web page.

Hope this clarifies the behavior.

Lars.

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userMichael Gage - Re: Gateway testing - where?  blueArrow
6/3/2006; 3:26:39 PM (reads: 1200, responses: 0)
Lars,

Can you do the experiment you describe while watching the apache error log? I'm curious if any errors are being reported to the error log that aren't appearing on the screen. An error such as "such and such is not defined at line ..... of ....." would be very helpful.

-- Mike

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userLars Jensen - Re: Gateway testing - where?  blueArrow
6/3/2006; 4:10:52 PM (reads: 1198, responses: 0)
Mike, there's nothing in the apache error log at all. -Lars.

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userGavin LaRose - Re: Gateway testing - where?  blueArrow
6/5/2006; 9:27:04 AM (reads: 1195, responses: 0)
Hi Lars (et al),

Is there an "Assignment Type" selector on the "Library Browser" page? I can't see one in the version of WeBWorK (2.1 or so) that I'm running on my development server. (Sam or Mike, did you add one?) I just did the following to see if I could duplicate your problem:

  • Entered the Library Browser,
  • Created a new set, and then added problems to it. I don't have an "Assignment Type" option on the Library Browser page, so I then
  • Entered Instructor Tools, selected the set, and clicked "Edit one set",
  • Changed the assignment type to "gateway/quiz", saved and got the gateway parameters, which I then corrected, and finally
  • Went back to the Library Browser and added a problem, saving the set afterwards.

Through all of this, once I'd set the assignment type to "gateway/quiz" it remained that way without changing. I'll have to get the latest version of WeBWorK to see if there's a difference in that.

Lars, you said you're running WeBWorK 2.2, right? Can you give me access to the course you're working with so that I can see the behavior first-hand?

Thanks,
Gavin

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userGavin LaRose - Re: Gateway testing - where?  blueArrow
6/5/2006; 1:32:17 PM (reads: 1174, responses: 0)
Hi Lars,

The plot thickens! I've tested the behavior you report on your server, and agree that the bug is clearly defined: changing the Assignment Type in the Set Detail page does not work. I can't look at the database to see what's going on there, but the Set Detail page doesn't show any change to the gateway/quiz assignment type.

So, I upgraded my development server to the latest version from the CVS, and I cannot duplicate the bug on my machine. So it's got to be something odd with either (a) the specific version of WeBWorK that you're running, assuming that it isn't the most current version from CVS, or (b) something with your set-up.

More anon,
Gavin

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userGavin LaRose - Re: Gateway testing - where?  blueArrow
6/6/2006; 3:46:20 PM (reads: 1173, responses: 0)
An update for anyone who is following this thread.

The problem appears to be a very odd database data error. After selecting a 'gateway' assignment type in the Set Detail page and saving the set, the assignment_type field in the mySQL database is correctly defined to be 'gateway'. However, when revisiting the Set Detail page, the data from the database isn't being correctly read into the set object: a dump of the fields and their values is as follows. 

  version_last_attempt_time =>
  version_time_limit => 0
  versions_per_interval =>
  time_interval =>
  version_creation_time => gateway
  assignment_type =>
  attempts_per_version =>
  problem_randorder =>

Looking in mySQL, the assignment_type field is defined to be 'gateway', version_creation_time is '0', and version_time_limit is 'null'. So somehow these are getting scrambled in the course of reading the data into the set object that's being used by the Set Detail page (which is generated by ProblemSetDetail.pm).

I'm not sure why this is. If someone else has some insight, it's welcome. We'll follow up when we have more information. The Set.pm file in ...lib/WeBWorK/DB/Record/ is fine.

Gavin

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userSam Hathaway - Re: Gateway testing - where?  blueArrow
6/6/2006; 5:47:49 PM (reads: 1147, responses: 0)
Hi Gavin, Lars,

This could be caused by the columns of the set table being ordered incorrectly. Lars, could you run the following SQL query:

show fields from coursename_set (replace coursename with the name of your course.)

You'd do this in the mysql console for the webwork database. Enter it with:

mysql -u webworkRead -p webwork

Thanks.
-sam

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userLars Jensen - Re: Gateway testing - where?  blueArrow
6/6/2006; 10:41:34 PM (reads: 1134, responses: 0)
Hi sam,

This is the result of the

show fields from test1_set

query. The name of the course is test1

Lars.

 

set_id  	text  	YES  	MUL  	NULL  	 
set_header 	text 	YES 	  	NULL 	 
hardcopy_header 	text 	YES 	  	NULL 	 
open_date 	text 	YES 	  	NULL 	 
due_date 	text 	YES 	  	NULL 	 
answer_date 	text 	YES 	  	NULL 	 
published 	text 	YES 	  	NULL 	 
version_last_attempt_time 	bigint(20) 	YES 	  	NULL 	
version_time_limit 	int(11) 	YES 	  	NULL 	 
versions_per_interval 	int(11) 	YES 	  	NULL 	 
time_interval 	int(11) 	YES 	  	NULL 	 
version_creation_time 	bigint(20) 	YES 	  	NULL 	 
assignment_type 	text 	YES 	  	NULL 	 
attempts_per_version 	int(11) 	YES 	  	NULL 	 
problem_randorder 	int(11) 	YES 	  	NULL

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userSam Hathaway - Re: Gateway testing - where?  blueArrow
6/7/2006; 12:17:08 AM (reads: 1135, responses: 0)
Mine looks like this:

 

set_id                   
set_header               
hardcopy_header          
open_date                
due_date                 
answer_date              
published                
assignment_type          
attempts_per_version     
time_interval            
versions_per_interval    
version_time_limit       
version_creation_time    
problem_randorder        
version_last_attempt_time

Looks like yours is out of order for some reason. I'm not sure why this would have happened, but you can fix it by modifying the file lib/WeBWorK/DB/Schema/SQL.pm:

Replace each occurence of:

 

my $stmt = "SELECT * FROM `$sqlTable` $where";

(This line appears twice, once in the gets subroutine, and once in the getAll subroutine.)

With:

 

my @fieldnames = $self->sqlFieldnames();
my $fieldnames = join(", ", @fieldnames);
my $stmt = "SELECT $fieldnames FROM `$sqlTable` $where";

I haven't tested this yet, but it shouldn't do any damage. I'll test it tomorrow.
-sam

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userLars Jensen - Re: Gateway testing - where?  blueArrow
6/7/2006; 12:58:41 PM (reads: 1113, responses: 0)
Hi Sam,

The above replacement resulted in this error when I tried to login to the course:

Warning messages

* DBD::mysql::st execute failed: Operand should contain 1 column(s) at /opt/webwork2/lib/WeBWorK/DB/Schema/SQL.pm line 229.

Error messages

DBD::mysql::st execute failed: Operand should contain 1 column(s) at /opt/webwork2/lib/WeBWorK/DB/Schema/SQL.pm line 229.

Call stack

The information below can help locate the source of the problem.

* in WeBWorK::DB::Schema::SQL::gets called at line 202 of /opt/webwork2/lib/WeBWorK/DB/Schema/SQL.pm

* in WeBWorK::DB::Schema::SQL::get called at line 1039 of /opt/webwork2/lib/WeBWorK/DB.pm

* in WeBWorK::DB::getUser called at line 179 of /opt/webwork2/lib/WeBWorK/Authen.pm

* in WeBWorK::Authen::verify called at line 227 of /opt/webwork2/lib/WeBWorK.pm

Lars.

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userSam Hathaway - Re: Gateway testing - where?  blueArrow
6/7/2006; 3:32:14 PM (reads: 1105, responses: 0)
Lars,

Sorry about that. I should not have put parens around $fieldnames. I've fixed it above and tested the code this time.
-sam

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userSam Hathaway - Re: Gateway testing - where?  blueArrow
6/7/2006; 3:39:11 PM (reads: 1116, responses: 0)
Hi,

This bug is fixed in lib/WeBWorK/DB/Schema/SQL.pm version 1.31 (for HEAD) and version 1.29.2.2 (for the rel-2-2-dev branch).

If you're running 2.2.x, you can update to the tip of the 2.2 dev branch as follows:

 

cvs update -r rel-2-2-dev

(Don't forget to restart the web server after you do this.)

HTH.
-sam

<| Post or View Comments |>

userLars Jensen - Re: Gateway testing - where?  blueArrow
6/7/2006; 4:01:07 PM (reads: 1105, responses: 0)
Hi Sam,

Thanks! The "Assignment type" now sticks and the extra blanks show up!

Is there (going to be) a rel-2-2-patches branch?

Lars.

<| Post or View Comments |>

userSam Hathaway - Re: Gateway testing - where?  blueArrow
6/7/2006; 9:03:09 PM (reads: 1118, responses: 0)
Hi Lars,

The rel-2-2-dev branch serves that purpose. (In addition, it also served as a staging area during the 2.2.0 feature freeze. That's why the name change.)
-sam

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Forum archive 2000-2006 -> Michael Gage - Annual WeBWorK happy hour at San Antonio AMS meeting

by Arnold Pizer -
inactiveTopicAnnual WeBWorK happy hour at San Antonio AMS meeting topic started 1/9/2006; 9:17:46 PM
last post 1/9/2006; 9:17:46 PM
userMichael Gage - Annual WeBWorK happy hour at San Antonio AMS meeting  blueArrow
1/9/2006; 9:17:46 PM (reads: 5594, responses: 0)
Annual WeBWorK happy hour at San Antonio AMS meeting
At the joint meetings in San Antonio, we will have a happy hour gathering of WeBWorK teachers, administrators, and anyone interested in WeBWorK. Come and compare notes and experiences, learn more, discuss new features, gripe about bugs, whatever, etc. We will leave from the entrance of the book exhibits at 4:30 on Friday, Jan 13 to go to a place (to be named later) which serves refreshments, and people are welcome go on to dinner together from there. We will also leave a message on the message boards under the name WeBWorK about where we are going in case someone cannot be at the book exhibits at exactly 4:30.

If you would like to get in touch with us at the meetings before then, we will be checking the message boards. We hope to see lots of people there.

Jeff Holt and John Jones
Posted by Michael Gage on 1/9/06; 9:18:30 PM
from the dept.

 

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Forum archive 2000-2006 -> John Jones - WeBWorK get together at joint meetings in San Antonio

by Arnold Pizer -
inactiveTopicWeBWorK get together at joint meetings in San Antonio topic started 12/29/2005; 12:25:36 PM
last post 12/30/2005; 11:28:43 AM
userJohn Jones - WeBWorK get together at joint meetings in San Antonio  blueArrow
12/29/2005; 12:25:36 PM (reads: 427, responses: 1)
At the joint meetings in San Antonio, we will have a happy hour gathering of WeBWorK teachers, administrators, and anyone interested in WeBWorK. Come and compare notes and experiences, learn more, discuss new features, gripe about bugs, whatever, etc.

We will leave from the entrance of the book exhibits at 4:30 on Friday, Jan 13 to go to a place (to be named later) which serves refreshments, and people are welcome go on to dinner together from there. We will also leave a message on the message boards under the name WeBWorK about where we are going in case someone cannot be at the book exhibits at exactly 4:30.

If you would like to get in touch with us at the meetings before then, we will be checking the message boards. We hope to see lots of people there.

Jeff Holt and John Jones

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userJohn Jones - Re: WeBWorK get together at joint meetings in San Antonio  blueArrow
12/30/2005; 11:28:43 AM (reads: 507, responses: 0)
Hi,

We are moving the departure time to 4:30 to reduce a time conflict with another event at the meeting.

Jeff Holt and John Jones

PS: So that people won't get confused now by reading the original post (and not this follow-up), we modified the original post to reflect the new time.

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Forum archive 2000-2006 -> Gavin LaRose - pagerror, refresh gif files

by Arnold Pizer -
inactiveTopicpagerror, refresh gif files topic started 11/7/2005; 1:55:56 PM
last post 11/8/2005; 2:50:43 PM
userGavin LaRose - pagerror, refresh gif files  blueArrow
11/7/2005; 1:55:56 PM (reads: 1096, responses: 6)
Hi all,

What is "pagerror.gif"? I'm finding a lot of error log messages from our Gateway test testing that complain about not finding a display module for pagerror.gif. But I can't figure out what pagerror.gif is supposed to be, or where it's supposed to be. Similarly for "refresh.gif".

Thanks,
Gavin

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userMichael Gage - Re: pagerror, refresh gif files  blueArrow
11/7/2005; 2:04:50 PM (reads: 1155, responses: 0)
Do you have a line number and script file name where the error is occuring?

-- Mike

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userGavin LaRose - Re: pagerror, refresh gif files  blueArrow
11/7/2005; 2:10:36 PM (reads: 1170, responses: 0)
Hi Mike,

The log message is the following: 

...[/webwork2/ma215f05/7/3/pagerror.gif] 
No display module found for path '/ma215f05/7/3/pagerror.gif/'. 
at /opt/www/webwork/webwork2/lib/WeBWorK.pm line 127.

Thanks,
Gavin

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userMichael Gage - Re: pagerror, refresh gif files  blueArrow
11/7/2005; 2:25:35 PM (reads: 1139, responses: 0)
Hi Gavin,

Something --- hard to say what right at the moment --- is returning a url to the browser asking it to fetch the relative path pagerror.gif

Since the browser was last pointed to /webwork2/ma215f05/7/3 it assumes it needs /webwork2/ma215f05/7/3/paperror.gif and asks for it.

The dispatcher in WeBWorK.pm (and URL.pm) has no clue what is being asked for and gives this error.

I'm afraid I can't guess what error sends back a reference to paperror.gif -- probably something with in the bowels of the Apache server perhaps? You might try

locate pagerror.gif

and see if you find something.

Hope this helps.

Take care,

Mike

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userGavin LaRose - Re: pagerror, refresh gif files  blueArrow
11/7/2005; 3:33:06 PM (reads: 1143, responses: 0)
Hi Mike,

Thanks. With a little further investigation, it appears to be the case that

  • the error is only generated by MSIE 6.0,
  • it is only generated on requests for /webwork2/ addresses (though it occurs for both homework and gateway test addresses),
  • it only occurs for requests for the ProblemSetList page, Problems in homeworks, and Gateway quizzes, and
  • it started when I upgraded WeBWorK from the CVS at the beginning of the semester.

I haven't tried upgrading from the CVS to see if some subtle change since the last time I did that has fixed the problem because we're "in production" and I don't want to elicit screams of protest if I break something.

Any thoughts or comments are welcome. Further announcements as events merit.

Gavin

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userSam Hathaway - Re: pagerror, refresh gif files  blueArrow
11/7/2005; 10:17:33 PM (reads: 1149, responses: 0)
pagerror.gif is the name of the icon that IE shows on error pages (like when it can't load a page. It's usually located at res://C:WINDOWSSystem32shdoclc.dll/pagerror.gif.

Here's someone who ends up with pagerror.gif appended to image URLs, but he was working with an IIS server: http://archives.neohapsis.com/archives/vuln-dev/2003-q4/0138.html

Not much else forthcoming. I assume you've checked the HTML that webwork is sending and haven't found any reference to this mystery file.

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userGavin LaRose - Re: pagerror, refresh gif files  blueArrow
11/8/2005; 2:50:43 PM (reads: 1185, responses: 0)
Hi Sam,

I went through with a find -exec grep pagerror.gif... in the WeBWorK directory and couldn't find anything, so I'm inclined to think that it's something to do with IE requesting the file for some reason. Thinking about it today, I'd bet that it's something to do with not finding some image that it needs from the images that jsMath mode uses to do its display. Not finding that, it looks for the "image not found" image, which of course doesn't exist either.

If this is the case, it's likely that when I update PG from the CVS there's a chance that the error may go away.

Thanks,
Gavin

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Forum archive 2000-2006 -> Nandor Sieben - Picture in students_ans differs in sets and librarybrowser

by Arnold Pizer -
inactiveTopicPicture in students_ans differs in sets and librarybrowser topic started 6/23/2005; 7:08:58 PM
last post 8/13/2005; 1:55:16 AM
userNandor Sieben - Picture in students_ans differs in sets and librarybrowser  blueArrow
6/23/2005; 7:08:58 PM (reads: 2050, responses: 14)
We have a problem where the students need to build a graph by typing in edges. To help with visualization we create a picture of the graph from these edges in our own answer evaluator and we set $ans_hash so that student_ans has this picture.

student_ans => $view

This previews the picture in the 'Entered' field in the asnwer table. This works perfectly in the library browser but there is an error when we put this problem into a set. In a set the picture is not updated with multiple submission. The first picture remains unchanged even if we change the submitted edges. The problem works, it accepts the correct answer and rejects the incorrect answer. Only the picture is not updated.

Is there anything done differently in the library browser and in a set? Is it a bug or do we need to change something? Is student_ans a wrong place to put this generated picture?

Nandor

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userMichael Gage - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/23/2005; 10:44:54 PM (reads: 2336, responses: 0)
The most likely problem is that the browser is caching the image. Try using shift-reload -- on most browsers this will force a refresh. If this makes the picture update than at least you know where the problem lies. There are subtle differences between the library and a regular problem set -- no big differences, but enough so that it might make a browser behave differently.

I would suggest that you add a 3 digit number to the address of the file holding the picture. Make the number depend on what is in the picture, so that when the picture changes the name of the file also changes.

Hope this helps.

--Mike

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userNandor Sieben - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/23/2005; 11:58:58 PM (reads: 2329, responses: 0)
> I would suggest that you add a 3 digit number to the address of the > file holding the picture. Make the number depend on what is in the > picture, so that when the picture changes the name of the file also > changes.

I don't know how to do this. It's not a static image, but a picture generated on the fly with the built in drawing macros so I am guessing that the address of the picture is generated automatically.

I am pretty sure it's not the browser. Here is why. I logged out. I moved to another computer and I used a different browser. I submitted a different answer for this problem. Still the picture I got was the one generated by the very first submission on the first computer. Reload, shift reload, view picture in separate window and reload, nothing works.

We use these generated pictures inside pg files all over. They always work, except in this case where the evaluator creates them. So I think something must be done differently in the library browser and sets when pictures are generated in evaluators or when pictures are displayed in the answer table. I am guessing that we are probably the first trying to put pictures in the answer table.

Nandor

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userNandor Sieben - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 12:21:09 AM (reads: 2312, responses: 1)
I have found the fix:

$pic->gifName($pic->gifName()."-$in");

It is still a question: why is this needed in a set but not in the library browser?

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userJohn Jones - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 2:00:15 AM (reads: 2313, responses: 0)
Hi,

In general, webwork tries to use cached copies of on-the-fly graphs to save time. Lots of students doing a graph-laden assignment can cause a pretty large load on the server. It happened to us once.

One stage of the caching mechanism is to distinguish graphs by their names, which contains the student name, problem seed, set name, problem number, and graph number within a problem. If any of those things change, then webwork will generate a different graph. It isn't bulletproof, but collisions here are pretty unlikely. Effectively, someone would have to make an assignment, and then change the pg file used for the problem without changing the seed or renumbering the problems, and both pg files would have to have on-the-fly graphs in them. Webwork also checks the change times of the pg file and the graph, so if there is a new copy of the problem file, it regenerates the graph.

The final check is to see if the problem is being rendered from the library browser. Those problems have only generic data (problem seed is usually 0, set name is always the same, etc.). So, while someone is browsing problems with graphs, it is pretty likely that this data will result in a name collision. So, the caching mechanism accounts for it. So, that is why rendering on-the-fly graphs was different in the library browser.

Manually changing the graph name like you are now doing is probably the right solution. Any other solution would either mean giving up on caching or setting a flag for certain images (like yours) to say "don't cache me", but the latter is as much work for the problem author as what you have above.

John

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userMichael Gage - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 1:07:08 PM (reads: 2597, responses: 0)
You can also use an extension generated by time() which gives you the "unix" time in seconds since some date -- something like 1119632502. This number will keep changing everytime you create a new picture.

Over the long term you may need to worry about filling up the directory where these images are stored (since there is no reuse of images). This won't be a problem in the beginning but eventually you might like to set a cron job to clear these images out. Using time() as part of the name makes it easy to tell how long ago the image was created.

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userJohn Jones - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 3:14:15 PM (reads: 2295, responses: 1)
Filling up your disk with these once used images would be a reason to impliment the dont-cache-me option for images instead of using the filename approach. Then the new images would simply replace the old image. I think this would be hard to do. Do you think it is worth it? If so, what should the semantics be? Maybe allow an option to init_graph of cache=> 0 and a function to set the option directly of $mygraph->setcache(0)?

John

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userNandor Sieben - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 3:23:06 PM (reads: 2309, responses: 0)
John, If I run the cron job you suggested some time ago to delete images not used for 2 weeks then I don't need to worry about this, do I?

Nandor

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userMichael Gage - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 3:44:25 PM (reads: 2601, responses: 0)
I don't think that it is worth it to implement a "don't cache me" option.

What might be worthwhile is to generate part of the file name based on the actual contents of the image. That way the same images reuse the same space. This is what we do with latex math images. With these images we have natural data to generate the hash.

I suspect that with png files we could use MD5 (http://userpages.umbc.edu/~mabzug1/cs/md5/md5.html) to generate a 128 bit signature for the image.

I don't know what the performance costs would be, but the idea behind the implementation would be quite straightforward.

By the way -- the latest version in the CVS has refined time measurements (to 1/1000 of a second) so that it's easier to measure the affect of a change on performance.

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userJohn Jones - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 7:43:10 PM (reads: 2290, responses: 0)
First for Nandor, the program remove_stale_images only looks at images generated from latex for equations. Those are shared system-wide. The on-the-fly graphics are temporary files stored within each course. There are other such files which accumulate during the semester, such as pdf's for hardcopy. You could have another cron job to delete ones of those which haven't been accessed recently. I just let them accumulate and then delete them when I eventually archive a course.

For Mike, I am a little unclear on your suggestion. The current idea is to not generate an on-fly-graph if we don't need to. If our test for whether or not we need the image is: generate the image and run md5 on that, we can't be saving any time. It would save some disk space if two different students produced exactly the same graph in their problems, but it probably isn't worth it for that.

Otherwise, you have to run md5 on the data used to generate the graph. For latex images, it is easy to get ahold of that data. However, for WWPlot objects, I don't think there is a function for that yet, and it doesn't sound like much fun to write. Of course if we added a function to serialize the graph, then we could use md5 on the result. We also wouldn't need to incorporate any other information in the filename of the graph since, if two graphs were generated by the same data, they better have the same image.

John

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userMichael Gage - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/24/2005; 9:12:48 PM (reads: 2295, responses: 0)
I see your point John, I hadn't thought my suggestion through. You do save space with this method, but it costs extra time. There probably is not a general method for generating MD5 data for any picture. For specific classes of pictures -- such as the ones Nandor is generating there might be some hope. If the graph is generated from some sort of matrix one could run MD5 on that and generate a number to tag on to the picture name. If this proves useful we could encapsulate a lot of the details in a macro so that it was fairly straightforward to implement in problems.

-- Mike

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userArnold K. Pizer - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/27/2005; 1:54:55 PM (reads: 2284, responses: 0)
Hi,

I'll add my two cents to this discussion. We already have the "flag" refreshCachedImages. I'm not 100% sure what this does in WW2 but I assume it means that if a problem contains $refreshCachedImages =1 then dvipng images of equations are not cached but are refreshed every time. I think what we should do is to refresh all cached images if this flag is set. Maybe it even does this now. Having a problem author remember to reset the name of the stored image, etc. is too complicated and to remember what $refreshCachedImages =1 does is even worst if it doesn't refresh all cached images (at this point I at least don't remember). Here's the verbiage from PG.pl.

 



	The following flags are set by ENDDOCUMENT:
	(1) showPartialCorrectAnswers  -- determines whether students are told which
	    of their answers in a problem are wrong.
	(2) recordSubmittedAnswers  -- determines whether students submitted answers
	    are saved.
	(3) refreshCachedImages  -- determines whether the cached image of the problem
	    in typeset mode is always refreshed (i.e. setting this to 1 means cached
	    images are not used).




Arnie 
            

            
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userNandor Sieben - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/28/2005; 1:12:13 AM (reads: 2234, responses: 
            0) 		
        
Setting refreshCashedImages to 1 does not solve the problem.
Nandor 
            
            
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userJohn Jones - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
6/28/2005; 12:40:08 PM (reads: 2208, responses: 
            0) 		
        
I
don't think refreshCachedImages does anything in webwork 2. Maybe it
was pure oversight, or maybe it was related to the fact that webwork 2
stored equation type images based on their content. They automatically
refresh if the content of the image changes.

In any case, it does seem reasonable to have refreshCachedImages act as
Arnie suggests, so it has its old meaning plus refreshing of on-the-fly
graphics images as well.


John 
            

            
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userJohn Jones - Re: Picture in students_ans differs in sets and librarybrowser  blueArrow
8/13/2005; 1:55:16 AM (reads: 2096, responses: 
            0) 		
        
Hi,


Setting 

$refreshCashedImages= 1;

will now force on-the-fly graphics for the problem to be regenerated every time the problem is rendered.


John 
            

            
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                Forum archive 2000-2006
                    -> Blake Thornton - Bizarre image generation problem
        

                        

                            by Arnold Pizer - 
                        

                

            


            

                        

                        


                

                    

                        
inactiveTopicBizarre image generation problem
          topic started 10/15/2004; 1:51:32 PM
last post 10/15/2004; 5:33:02 PM		
        
 
      
userBlake Thornton - Bizarre image generation problem  blueArrow
10/15/2004; 1:51:32 PM (reads: 1306, responses: 
            7) 		
        
Perhaps
this is a bug that has been fixed that we haven't updated, but here is
the problem: it seems that webwork successfully generates the images,
but when building the webpage it places the images in the wrong
locations on the webpage.


Here is a specific example:
 


DOCUMENT();


loadMacros(PG.pl, PGbasicmacros.pl, PGchoicemacros.pl, PGanswermacros.pl, PGauxiliaryFunctions.pl );



TEXT(beginproblem());


BEGIN_TEXT


Find the amount \( A \) in an account after \( t \) years if


\[
\frac{dA}{dt} = 0.12A
\]


where \( A(0) = 5250 \)


$PAR


\( A(t) \) = \{ ans_rule(15) \} 


$PAR


END_TEXT


ANS(fun_cmp("5250* exp(0.12*t)", var=>['t']));


ENDDOCUMENT();
 


What is displayed on my screen in image mode (with the tex converted to images):


Find the amount \( A \) in an account after \( t \) years if


\[
A(t)
\]


where \( A(0) = 5250 \)
$PAR


\( A(t) \) = \{ ans_rule(15) \} 


$PAR


END_TEXT
 


Bizarre.  Now, the amazing thing is that the following displays correctly:
 



BEGIN_TEXT


Find the amount \( A \) in an account after \( t \) years if


\[ 
\frac{dA}{dt} = A(0.12)
\]


where \( A(0) = 5250 \)


$PAR


\( A(t) \) = \{ ans_rule(15) \} 


$PAR


END_TEXT
 


Everything displays correctly in the other display modes, but not in image mode.


Any ideas? 
            

            
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userJohn Jones - Re: Bizarre image generation problem  blueArrow
10/15/2004; 3:27:40 PM (reads: 1495, responses: 
            0) 		
        
Can
you view the faulty page, then have your browser give you the page
source? Down near the bottom is the html for the problem. Select the
full image tags, and post them. That should let us see what the raw
latex used for the images, and the image paths. When posting, you can
use the html tags

  <pre>
   pasted <img> tags
   </pre>

so that things should come through without having to add extra backslashes.


John 
            

            
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userMichael Gage - Re: Bizarre image generation problem  blueArrow
10/15/2004; 3:28:07 PM (reads: 1507, responses: 
            0) 		
        
This
sounds like a caching problem. A mistake in generating the image at
some point is now persisting. The first thing to try is to use
shift-refresh on the browser to see if the browser itself is caching
the image. (Or quit and relaunch the browser -- or check to see if
others see the same problem.) 

WeBWorK itself (within ImageGenerator.pm) also tries to cache the
images and it's possible that having generated an incorrect image it
refuses to create a new one on the grounds that it has already created
this image. This fits with all of the information you've given.

Correcting this latter situation cleanly is a bit more delicate, and I
can't give a full answer off the top of my head. Search through
global.conf for "equation" and look at those locations for images and
references to images that have been created and don't need to be
created again. 

            
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userBlake Thornton - Re: Bizarre image generation problem  blueArrow
10/15/2004; 3:55:44 PM (reads: 1519, responses: 
            0) 		
        
Thanks for the quick responses!

I don't understand webwork's internal caching, but I don't think it is
a caching problem. This problem first occured in the editing page
(where I was editing the problem-- webwork certainly shouldn't cache
those images). In addition, I viewed the actual files on the server and
they match up with what I'm seeing (i.e., they are wrong).

I posted the html source of the html file, the pg file and the png
files that I downloaded from /opt/webwork2/htdocs/tmp/equations. These
can be found here:


http://www.math.wustl.edu/~blake/tmp/


Thanks for any insights! 
            

            
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userJohn Jones - Re: Bizarre image generation problem  blueArrow
10/15/2004; 4:31:31 PM (reads: 1507, responses: 
            0) 		
        
It
comes up fine on my system. There is a latex error in the solution part
(A = A_0e^{0.12 t) should end in a brace, not a parenthesis), but I
don't think that is really the source of your problem.

Maybe you should remove the images and view the problem again and see
what happens. To remove old images, as superuser, run the
remove_stale_images script to clean them all out:

 remove_stale_images --delete --days=0

Does it then produce exactly the same image files?


John 
            

            
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userBlake Thornton - Re: Bizarre image generation problem  blueArrow
10/15/2004; 4:58:31 PM (reads: 1494, responses: 
            0) 		
        
John,


Thanks for the ideas.  I fixed the tex error and it wasn't it.  But it worked perfectly after running remove_stale_images!!!


Okay, so any theories on why?  Should I plan to run this every once in a while?


Thanks for the help!!
Blake 
            

            
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userJohn Jones - Re: Bizarre image generation problem  blueArrow
10/15/2004; 5:09:25 PM (reads: 1507, responses: 
            0) 		
        
My
only idea on how it happened is that there was an attempt to generate
images which went wrong (some other bad latex being involved) and led
to an image being mislabelled. I haven't seen that before - it may take
some experimentation with a clean system and problems with faulty latex
in them.

On doing a complete flush of images, I wouldn't do it that often. Then
again, I haven't seen a mis-labeled image like this one before. I have
a server for which 2 weeks means 150,000 images, so I delete ones which
haven't been used in more than two weeks (same command, but with
days=14). This would not have picked up this problem if the image kept
on being accessed though.


John 
            

            
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userBlake Thornton - Re: Bizarre image generation problem  blueArrow
10/15/2004; 5:33:02 PM (reads: 1506, responses: 
            0) 		
        
Well, I'll keep this in mind if it occurs again-- I will certainly put this command in my bag of tricks.


Thanks again! 
            

            
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                Forum archive 2000-2006
                    -> Sherman Wong - Viewing Problem with Library Browser
        

                        

                            by Arnold Pizer - 
                        

                

            


            

                        

                        


                

                    

                        
inactiveTopicViewing Problem with Library Browser
          topic started 10/6/2004; 12:14:45 PM
last post 10/18/2004; 5:51:34 PM		
        
 
      
userSherman Wong - Viewing Problem with Library Browser  blueArrow
10/6/2004; 12:14:45 PM (reads: 2281, responses: 
            12) 		
        
There
seems to be a problem with the Library Browser in WeBWorK 2.0.1 when
viewing setDerivatives1 in the template directory. When I attempt to
view these problems and I select more than 5 problems, I get
essentially a blank screen. If I select 5, I can view the first 5
problems, but I can't view the next five or any subsequent problem. The
Library Browser should have a way of allowing one to view the
subsequent problems if, for some reason, it can't display a given
problem.

The workaround that works is to select for "display mode" "None". This
option permits one to "Try it" on the problems and to page to the next
group of problems.

The problems that seem to be causing the viewing problem are
nsc2s10p1.pg, nsc2s10p2.pg, and nsc2s10p3.pg. Oddly enough, there is no
viewing problem when using an earlier version of WeBWorK.


Can you explain why these problems are stalling the Library Browser?


Thank you.
Sherman 
            

            
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userMichael Gage - Re: Viewing Problem with Library Browser  blueArrow
10/6/2004; 12:26:34 PM (reads: 2539, responses: 
            1) 		
        
I
can't reproduce this using the Safari browser. I get the first 20
problems generated fairly quickly and a button at the bottom of the
page which links to the next 20. You might try limiting the number of
problems to 5 instead of 20. See if that helps. It might just be a
matter of browser/computer speed. 

The three problems you mention all have "on-the-fly" graphics --
perhaps something is making it hard for these graphics to be generated
or to load into the browser.


Using alternate viewing modes, such as "none" or "jsMath" is also an option when you run into this kind of problem.


-- Mike 
            

            
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userJohn Jones - Re: Viewing Problem with Library Browser  blueArrow
10/6/2004; 2:13:02 PM (reads: 2542, responses: 
            1) 		
        
For the three problems you mention, if you click on Try it, do the problems come up?


John 
            

            
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userSherman Wong - Re: Viewing Problem with Library Browser  blueArrow
10/6/2004; 2:39:01 PM (reads: 2845, responses: 
            0) 		
        
No,
when I click on "Try it", nothing appears for any of the three
problems. Because the graphics in the 3 problems are "on-the-fly",
there must be "something" wrong with our configuration of version
2.0.1, since the graphics do appear on version 1.9 of WeBWorK. 
            
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userSherman Wong - Re: Viewing Problem with Library Browser  blueArrow
10/6/2004; 2:47:12 PM (reads: 2884, responses: 
            0) 		
        
I tried your suggestion to use jsMath, but to no avail.  
The only option that circumvents the difficulty in viewing the "on-the-fly" graphics for the 3 cited problems is "None". 
            
            
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userMichael Gage - Re: Viewing Problem with Library Browser  blueArrow
10/6/2004; 3:29:33 PM (reads: 2527, responses: 
            0) 		
        
The
most likely thing wrong with your setup is that the on-the-fly graphics
are being created in one directory and your browser is looking for the
images in another. This means adjusting some variables in global.conf
so that they match up. You should also check the error log of the
apache server, since that will give you any information if a graphic
fails to be created, or if the browser tries to find the graphic in a
different director from the one where it is being created.

Since the problem appears to be the "on the fly" graphics, rather than
displaying equations, it makes sense that changing from "images" to
"jsMath" won't change anything.


-- Mike 
            

            
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userSherman Wong - Re: Viewing Problem with Library Browser  blueArrow
10/7/2004; 7:51:23 AM (reads: 2533, responses: 
            0) 		
        
I
relayed your suggestion to the fellow who works on seeing that the
program performs as it ought to. He told me that the browser was
looking at the correct file but that the file was of size 0 MB. This
problem of the misdirection of the browser occurred before when we were
testing WeBWorK 1.9.


Has there been any changes to the PG macro that handles such graphics?


Sherman 
            

            
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userMichael Gage - Re: Viewing Problem with Library Browser  blueArrow
10/7/2004; 8:23:30 AM (reads: 2513, responses: 
            0) 		
        
If
the contents of the file hasn't been created then there may messages in
the error log. It could be a problem of getting GD to work properly,
although if images mode for equations works then it is probably not GD,
since that mode also uses GD to create the images. There haven't been
any substantial changes made to these PG macros in some time.

You might want to remove the 0 MB file between tests since some caching
is performed by WeBWorK and you want to make sure that it recreates the
file. Pictures can be difficult to debug because the browsers also
cache images -- use shift reload (refresh) often to insure that the
browser is always getting the latest informationi. 

            
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userSherman Wong - Re: Viewing Problem with Library Browser  blueArrow
10/7/2004; 10:19:41 AM (reads: 2505, responses: 
            0) 		
        
Thank you for the suggestion about emptying the cache in the browser.  


I'll pass on your other suggestion regarding the deletion of the 0 MB file.


Sherman 
            

            
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userBjorn Nelson - Re: Viewing Problem with Library Browser  blueArrow
10/8/2004; 10:20:21 AM (reads: 2489, responses: 
            0) 		
        
Hello, I work with Sherman.  This actually relates to my post:
http://webhost.math.rochester.edu/webworkdocs/discuss/msgReader$2832 [$graph->draw not drawing]

Unfortunately, my post got mangled but I don't think you need to parse
it. From my debugging, I don't think it's a problem with insertGraph,
but rather in the process of creating the $graph object. I am trying to
follow it in the libraries.

Do you guys know of a way to debug web based perl? I know about perl
-d, but I don't know of any tools for web based perl besides writing
variables to a log file. I was looking at wwsh and I realize it's used
to browse the classes. Can I use this to browse classes when they are
used as an object? Is it just used to find the methods of classes?


Thanks,
Bjorn 
            

            
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userBjorn Nelson - Re: Viewing Problem with Library Browser  blueArrow
10/8/2004; 10:29:57 AM (reads: 2511, responses: 
            0) 		
        
btw,


This is the version of gd and the gd module


gd-2.0.25,1         A graphics library for fast creation of images
p5-GD-2.15          A perl5 interface to Gd Graphics Library version2 
            

            
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userBjorn Nelson - Re: Viewing Problem with Library Browser  blueArrow
10/8/2004; 1:26:40 PM (reads: 2514, responses: 
            1) 		
        
update,

I spoke with Mike and he suggested checking permissions and error logs.
I had recursively given the "courses" directory ownership to the apache
user account. Owner has full access to the directory.


I am getting an error:
httpd in free(): error: modified (page-) pointer
[Fri Oct  8 17:10:44 2004] [notice] child pid 52284 exit signal Abort trap (6)

I checked the resources for apache and it's given unlimited resources.
The FreeBSD init (or rc) script for apache assigns it's resource
profile to the www class. I defined this in the /etc/login.conf to
point to default which in turn is set for unlimited resources.


apache version is 1.3.31 using webwork 2.0.1.


-Bjorn 
            

            
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userBjorn Nelson - Re: Viewing Problem with Library Browser  blueArrow
10/18/2004; 5:51:34 PM (reads: 2732, responses: 
            0) 		
        
What does the number in the cached images mean?


For instance, what does 463 come from:
/usr/local/webwork2/courses/MTH9997/html/tmp/gif/professor-463-setFinal_Exam_Review_VIIprob1image1.png


compared to 64:
/usr/local/webwork2/courses/MTH9997/html/tmp/gif/professor-64-setFinal_Exam_Review_VIIprob1image1.png


on another machine using the same PG.  Why is it different?  Are these just unique numbers?


-Bjorn 
            

            
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                Forum archive 2000-2006
                    -> Doug Drinen - Images not displaying in Mozilla Firefox --- very strange
        

                        

                            by Arnold Pizer - 
                        

                

            


            

                        

                        


                

                    

                        
inactiveTopicImages not displaying in Mozilla Firefox --- very strange
          topic started 9/1/2004; 1:38:15 PM
last post 8/1/2005; 12:56:05 PM		
        
 
      
userDoug Drinen - Images not displaying in Mozilla Firefox --- very strange  blueArrow
9/1/2004; 1:38:15 PM (reads: 2745, responses: 
            2) 		
        
Firefox 0.8 on Linux Red Hat 9, WeBWorK 2.0

I created a very simple problem containing five integrals. I built a
set with just that problem. I went to do the set, and one of the
integrals wasn't there. The other four integrals appeared as images
(just as they should), but the fifth image didn't show up. The answer
box was there, just no question.

So I went and looked at each of the 30 students' sets. Of the 30, 24
were just fine. 6 had an image missing, just like mine (although it
wasn't the same image in every case).

So I looked at the html source. It referred to an image. I SSHed into
the WeBWorK box, tracked down that image and sure enough, there it was,
just where it was supposed to be. I went back to the browser and
entered the path to just that image and it displayed just fine. 

But no matter what I do, it does not show up when I go to work that
problem. I've tried refreshing the page, logging out and back in,
nothing works. The page displays perfectly in Konqueror, Opera, galeon,
and Safari. Only Firefox causes a problem.


This is clearly a Firefox problem, not a WeBWorK problem.  I'm posting it here in order to:


(1)  ask if anyone has seen similar behavior and/or other bizarre Firefox/WeBWorK issues.

(2) warn you that, if students call you wondering why their WeBWorK
problem looks funny, you might want to ask them what browser they're
using before throwing in the towel. 

            
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userJohn Jones - Re: Images not displaying in Mozilla Firefox --- very strange  blueArrow
9/1/2004; 3:29:12 PM (reads: 3076, responses: 
            1) 		
        
This
is the first case I have heard of in a recent browser other than IE. It
seems especially odd since recent linux/mozilla seems to be fine, and
they should be based on essentially the same display engine. On the
bright side, you probably don't have many students using linux-firefox.

In the realm of weird display problems, we encountered the "Peekaboo
Bug" in explorer 6. If you have a very long problem (like in set 0),
then explorer will make some of the text disappear. Reloading can make
it worse. Slowing dragging a window over the text can get it to
reappear. We seemed to be able to fix that with 
* {zoom: 1;}

in our template file.  I don't claim to understand why this solved the problem, but it was a relief to find it.


John 
            

            
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userThomas Hagedorn - Re: Images not displaying in Mozilla Firefox --- very strange  blueArrow
8/1/2005; 12:56:05 PM (reads: 1973, responses: 
            0) 		
        
I've
been running into a similar problem with Firefox on a Powerbook.
Equation images can get displayed in a fuzzy manner and sometimes the
problem is duplicated on top of itself but to the side so that it's one
big mess. Often, it will be one part of one problem that has this
display problem and the rest of the problem will be fine. When tried in
IE or Safari, the problem looks fine. And the .pdf file is fine too.


-Tom 
            

            
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