Re: Wrong Response returned for a Request

2011-07-30 Thread Robert Elliot

On 28 Jul 2011, at 10:16, Mark Thomas wrote:

 On 28/07/2011 07:34, Robert Elliot wrote:
 
 
 
 
 On 28 Jul 2011, at 00:24, David Rees dree...@gmail.com wrote:
 
 But perhaps this issue applies:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50189
 
 -Dave
 
 Thanks very much for the pointer - however, we're using mod_proxy rather 
 than mod_jk so presumably this wouldn't apply?
 
 mod_proxy_ajp or mod_proxy_http?
 
 If mod_proxy_ajp, then it is possible that this issue might occur (I
 haven't checked the source code or tested it to be sure).
 
 Mark

Mod_proxy_http.  We enabled the access valve with a log pattern that included 
the number of bytes in the response in order to be able to match requests to 
responses at the Tomcat level and saw that the correct responses were being 
returned there but incorrect ones then returned by HTTPD/mod_proxy.  As we were 
using an old version of HTTPD we've upgraded it (from 2.2.3 to 2.2.19), and 
thus far we've been unable to reproduce the problem again.  Thanks for the help.



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Re: Wrong Response returned for a Request

2011-07-28 Thread Robert Elliot




On 28 Jul 2011, at 00:24, David Rees dree...@gmail.com wrote:

 On Wed, Jul 27, 2011 at 10:39 AM, Mark Thomas ma...@apache.org wrote:
 On 27/07/2011 17:23, Robert Elliot wrote:
 We are using Tomcat 6.0.29, and occasionally experiencing concurrency issues
 which look very much like the wrong response is being returned for a 
 request.
 While we cannot reproduce it reliably, it seems to happen when Keep-Alive 
 is turned on.
 
 I noticed this issue with Tomcat 7:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50957
 
 Is there any chance that issue also exists in 6.0.29?
 
 None.

Thanks for the confirmation - it seemed unlikely.

 
 But perhaps this issue applies:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50189
 
 -Dave
 
Thanks very much for the pointer - however, we're using mod_proxy rather than 
mod_jk so presumably this wouldn't apply?

Rob

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Re: Wrong Response returned for a Request

2011-07-28 Thread Pid
On 28/07/2011 07:34, Robert Elliot wrote:
 
 
 
 
 On 28 Jul 2011, at 00:24, David Rees dree...@gmail.com wrote:
 
 On Wed, Jul 27, 2011 at 10:39 AM, Mark Thomas ma...@apache.org wrote:
 On 27/07/2011 17:23, Robert Elliot wrote:
 We are using Tomcat 6.0.29, and occasionally experiencing concurrency 
 issues
 which look very much like the wrong response is being returned for a 
 request.
 While we cannot reproduce it reliably, it seems to happen when Keep-Alive 
 is turned on.

 I noticed this issue with Tomcat 7:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50957

 Is there any chance that issue also exists in 6.0.29?

 None.
 
 Thanks for the confirmation - it seemed unlikely.
 

 But perhaps this issue applies:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50189

 -Dave

 Thanks very much for the pointer - however, we're using mod_proxy rather than 
 mod_jk so presumably this wouldn't apply?

In most cases this symptom turns out to be a result of the session,
request or response object being retained (perhaps as an instance field
in a Servlet) where they should not be.

Can you double check your code to see if this is possible?


p

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Re: Wrong Response returned for a Request

2011-07-28 Thread Robert Elliot
- Original Message -
 From: Pid p...@pidster.com
 To: Tomcat Users List users@tomcat.apache.org
 Sent: Thursday, 28 July, 2011 9:07:13 AM
 Subject: Re: Wrong Response returned for a Request

  On 27/07/2011 17:23, Robert Elliot wrote:
  We are using Tomcat 6.0.29, and occasionally experiencing
  concurrency issues
  which look very much like the wrong response is being returned
  for a request.
  While we cannot reproduce it reliably, it seems to happen when
  Keep-Alive is turned on.

 In most cases this symptom turns out to be a result of the session,
 request or response object being retained (perhaps as an instance
 field
 in a Servlet) where they should not be.
 
 Can you double check your code to see if this is possible?
 

Unfortunately it's a third party application we're running.  However as a gut 
feeling I'd expect a straightforward bug like that to be easier to reproduce; 
we've spent a day chucking between 100 and 1200 concurrent clients at it and we 
only see the problem very occasionally.  Oddly once it has happened it keeps 
happening for a period - and then stops.

I think we need to think harder about how to diagnose it - at the moment we 
can't pin it to a specific layer, it could be the application (most likely), 
Tomcat, mod_proxy or Apache HTTPD (we're running 2.2.3). I only asked here as 
the bug sounded so like what we were seeing.

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Re: Wrong Response returned for a Request

2011-07-28 Thread Pid
On 28/07/2011 09:26, Robert Elliot wrote:
 - Original Message -
 From: Pid p...@pidster.com
 To: Tomcat Users List users@tomcat.apache.org
 Sent: Thursday, 28 July, 2011 9:07:13 AM
 Subject: Re: Wrong Response returned for a Request

 On 27/07/2011 17:23, Robert Elliot wrote:
 We are using Tomcat 6.0.29, and occasionally experiencing
 concurrency issues
 which look very much like the wrong response is being returned
 for a request.
 While we cannot reproduce it reliably, it seems to happen when
 Keep-Alive is turned on.

 In most cases this symptom turns out to be a result of the session,
 request or response object being retained (perhaps as an instance
 field
 in a Servlet) where they should not be.

 Can you double check your code to see if this is possible?

 
 Unfortunately it's a third party application we're running.  

Ah.

 However as a gut feeling I'd expect a straightforward bug like that to be 
 easier to reproduce; we've spent a day chucking between 100 and 1200 
 concurrent clients at it and we only see the problem very occasionally.  

Try reducing the number of connector threads, try 10 and work down from
there.

 Oddly once it has happened it keeps happening for a period - and then
stops.

Maybe not.  Speculation: once the JVM is hot, JIT optimisation might
reduce the window size further.

 I think we need to think harder about how to diagnose it - at the moment we 
 can't pin it to a specific layer, it could be the application (most likely), 
 Tomcat, mod_proxy or Apache HTTPD (we're running 2.2.3). I only asked here as 
 the bug sounded so like what we were seeing.

Fair enough.


p


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Re: Wrong Response returned for a Request

2011-07-28 Thread Mark Thomas
On 28/07/2011 07:34, Robert Elliot wrote:
 
 
 
 
 On 28 Jul 2011, at 00:24, David Rees dree...@gmail.com wrote:
 
 On Wed, Jul 27, 2011 at 10:39 AM, Mark Thomas ma...@apache.org wrote:
 On 27/07/2011 17:23, Robert Elliot wrote:
 We are using Tomcat 6.0.29, and occasionally experiencing concurrency 
 issues
 which look very much like the wrong response is being returned for a 
 request.
 While we cannot reproduce it reliably, it seems to happen when Keep-Alive 
 is turned on.

 I noticed this issue with Tomcat 7:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50957

 Is there any chance that issue also exists in 6.0.29?

 None.
 
 Thanks for the confirmation - it seemed unlikely.
 

 But perhaps this issue applies:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50189

 -Dave

 Thanks very much for the pointer - however, we're using mod_proxy rather than 
 mod_jk so presumably this wouldn't apply?

mod_proxy_ajp or mod_proxy_http?

If mod_proxy_ajp, then it is possible that this issue might occur (I
haven't checked the source code or tested it to be sure).

Mark



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Re: Wrong Response returned for a Request

2011-07-27 Thread Mark Thomas
On 27/07/2011 17:23, Robert Elliot wrote:
 Hi
 
 We are using Tomcat 6.0.29, and occasionally experiencing concurrency issues 
 which look very much like the wrong response is being returned for a request. 
  While we cannot reproduce it reliably, it seems to happen when Keep-Alive is 
 turned on.
 
 I noticed this issue with Tomcat 7:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50957
 
 Is there any chance that issue also exists in 6.0.29?

None.

Mark



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Re: Wrong Response returned for a Request

2011-07-27 Thread David Rees
On Wed, Jul 27, 2011 at 10:39 AM, Mark Thomas ma...@apache.org wrote:
 On 27/07/2011 17:23, Robert Elliot wrote:
 We are using Tomcat 6.0.29, and occasionally experiencing concurrency issues
 which look very much like the wrong response is being returned for a request.
 While we cannot reproduce it reliably, it seems to happen when Keep-Alive is 
 turned on.

 I noticed this issue with Tomcat 7:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=50957

 Is there any chance that issue also exists in 6.0.29?

 None.

But perhaps this issue applies:
https://issues.apache.org/bugzilla/show_bug.cgi?id=50189

-Dave

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