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From John Wiles <j...@iotis.org>
Subject RE: JSP Page "hangs"... clues?
Date Wed, 10 Feb 2010 23:17:52 GMT
One thing I'd look for is a null pointer that isn't being taken care of properly in the code.
I've seen these cause jsp pages to not complete and appear to have caused any javascript in
the page to hang as well.


-----Original Message-----
From: Jordan Michaels [mailto:jordan@viviotech.net] 
Sent: Wednesday, February 10, 2010 3:27 PM
To: Tomcat Users List
Subject: Re: JSP Page "hangs"... clues?

Yeah, it's hanging permanently. We've let it sit there for what... 15 
mins or so? Which should be plenty since no one is using it right now 
except us.

Yeah, I know what you mean about the logs too. I'm very familiar with 
that happening and how to address it, but this time there's nothing in 
the logs at all. Makes it really hard to diagnose. =(

And yeah, I'm sure it's something server-side. I should have mentioned 
it in the first post, but we watched the traffic between the browser 
(several browsers actually) and the server and it was all the same. The 
browser would perform the request, the server would respond with part of 
the page (with send/ack's all throughout) and at the very end the 
browser would send a "okay, I got that last packet" message but the 
server won't send anything else.

Warm regards,
Jordan Michaels
Vivio Technologies
http://www.viviotech.net/
Open BlueDragon Steering Committee
Railo Community Distributions


Joseph Morgan wrote:
> Depends on if your machine can handle the memory load of everything on
> it.  
> 
> Is it hanging indefinitely... ie., does it ever come back??  I also
> suspect that you've verified that Tomcat is actually hanging and it's
> not just that the browser is, for some reason, not displaying
> everything.  That is, have you hit the page with something like Curl to
> be sure?? 
> 
> What I'm getting at is that I'm really good at causing Tomcat to run out
> of memory, but I always get the error dump in the logs.
> 
> -----Original Message-----
> From: Jordan Michaels [mailto:jordan@viviotech.net] 
> Sent: Wednesday, February 10, 2010 2:12 PM
> To: Tomcat Users List
> Subject: Re: JSP Page "hangs"... clues?
> 
> Hey Joseph,
> 
> Honestly I'm not sure about the code. We didn't write the code for it 
> and I haven't dug around in that part of it because the first few 
> requests seem to go through without a hitch.
> 
> We doubled the Xmx value from 512 to 1024 and added the MaxPermSize so 
> I've been going under the impression that if those were part of the 
> problem that I should be able to pull at least a few more hits out of 
> the page, right?
> 
> Warm regards,
> Jordan Michaels
> Vivio Technologies
> http://www.viviotech.net/
> Open BlueDragon Steering Committee
> Railo Community Distributions
> 
> 
> Joseph Morgan wrote:
>> Jordan,
>>
>> It sounds to me like a memory issue as well, but you should see an
>> OutOfMemory error in the logs, or so I would think.
>>
>> Is the page (or the actions within it) caching anything in the context
>> or session? 
>>
>> Joe
>>
>> -----Original Message-----
>> From: Jordan Michaels [mailto:jordan@viviotech.net] 
>> Sent: Wednesday, February 10, 2010 1:53 PM
>> To: users@tomcat.apache.org
>> Subject: JSP Page "hangs"... clues?
>>
>> We have an interesting situation and I'm wondering if anyone has any 
>> ideas on where we could look for possible solutions.
>>
>> We have a JSP page that performs a large mysql query of product titles
> 
>> (just the names). The list is then spit out on the page with
> drill-down 
>> links. Pretty simple really. The problem is that just after a tomcat 
>> restart, the first and occasionally the second and third requests will
> 
>> process all the way just fine, but most subsequent requests will
> "hang" 
>> on a random record. Occasionally one will go all the way through, but 
>> most will hang.
>>
>> Let me clarify, we restart tomcat, hit the page, and the page loads 
>> fine. We hit refresh once or twice, and the page will fail to load 
>> fully. The page will hang after a random product title and just stop 
>> responding. You can click on any other page on the site, but this one 
>> page with the large product listing query hangs in random spots.
>>
>> We've studied this intently. The server this is running on is a CentOS
> 
>> 4, 32-bit box with 1.5 GB RAM, Apache 2, and mod_jk.
>>
>> Our first thought was memory issues. We increased Tomcat's memory
> using 
>>   the setenv.sh file, which now contains the following line:
>>
>> JAVA_OPTS="-Xms128m -Xmx1024m -Xss256m -XX:MaxPermSize=256m "; export 
>> JAVA_OPTS
>>
>> We've verified that the settings are in place by using the "ps ax" 
>> command and making sure the java process includes the updated
> settings. 
>> Unfortunately, this seems to have no effect at all.
>>
>> We then reviewed the logs: catalina.out, mod_jk.log, and apache's
>> error_log, among others. We monitored these logs using "tail" so we
>> could see if any errors were thrown as we hit the page. No errors were
>> thrown if the request went through good or it failed. The logs were 
>> completely quiet.
>>
>> We've updated Tomcat, mod_jk, the JVM, and the MySQL driver to the 
>> absolute latest versions available as of this writing.
>>
>> Does anyone have any clues as to where we might look for what is 
>> happening to make this one page hang? It still feels like a memory 
>> issue, but with nothing in the logs and no indicators other then the 
>> problem itself, we'd appreciate any suggestions on what to look for at
> 
>> this point.
>>
>> Thank you in advance!
>>
> 
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