[Fwd: Re: [users@httpd] 503 status seems to get cached - how do I disable caching?]

[André Warnier <aw...@ice-sa.com>]

Rainer, do you want to have a go at this one ?

-------- Original Message --------
Subject: Re: [users@httpd] 503 status seems to get cached - how do I 
disable 	caching?
Date: Tue, 9 Jun 2009 15:37:25 -0500
From: Jenny Brown <sk...@gmail.com>
Reply-To: users@httpd.apache.org
To: users@httpd.apache.org
References: 
<ff...@mail.gmail.com>	 
<4A...@ice-sa.com>	 
<ff...@mail.gmail.com>	 
<ff...@mail.gmail.com>	 
<4A...@ice-sa.com>

Regarding the possibility of hung AJP sockets:

That's an interesting question.  I have a dev environment where I
could test it out, though it'll be a while before I get an opportunity
to do so.  If I can confirm that the absence of pending requests makes
the response time faster, I'll let you know.  Likewise if that's not
the issue, I'm back to the drawing board on it.

Thanks for the ideas.

Jenny Brown


On Mon, Jun 8, 2009 at 1:13 PM, André Warnier<aw...@ice-sa.com> wrote:
> Jenny Brown wrote:
>>
>> On Mon, Jun 8, 2009 at 12:50 PM, Jenny Brown<sk...@gmail.com> wrote:
>>>>
>>>> What you should really try, is to use the browser to access that same
>>>> URL
>>>> directly on Tomcat, without going through Apache, and see how long you
>>>> have
>>>> to wait there to get an answer after you start Tomcat.
>>>
>>> Hitting tomcat directly on port 8080 is very fast.  That difference in
>>> speed is what led me to believe that apache seemed to be caching.
>>
>> To clarify this a bit:
>>
>> In a single web browser, I can load
>> http://www.myserver.com:8080/manager/html/ in tomcat and see results,
>> and load http://www.myserver.com/manager/html/ in another window
>> (routes through apache, then ajp to tomcat) and see 503 -- at the same
>> time.
>>
>> That is, tomcat is up, the manager web app is answering requests, and
>> I can interact with it normally, for a significant amount of time,
>> while apache continues to say it can't get to it.
>>
>>
> Allright, so you have done your testing properly.  I just wanted to make
> sure you were looking at the right issue (I've had webapps that took 10
> minutes to get ready to process requests).
>
> And you are using mod_proxy_ajp as a connector, with which I am not
> familiar, so I'll just dream up a scenario for the issue, and maybe a
> specialist can tell us if I'm wrong.
>
> Let's imagine that there is a limited pool of mod_proxy_ajp threads or
> processes that can potentially forward requests to Tomcat.  Say there are 15
> of them, no more.
> Now 15 requests are issued to Apache at the same time, which should get
> proxied to Tomcat.  Each request is processed by one of the mod_proxy_ajp
> threads, they all set up a connection to Tomcat, and send their request.
> Next, Tomcat goes down.  The ajp threads are still waiting for a response.
>  They will keep waiting until some timeout occurs.
> Now more requests arrive in httpd, really for Tomcat.
> But because the 15 ajp threads are busy waiting, these requests have to wait
> (for a free ajp thread).
> Now Tomcat comes back up, but of course that does not help the apache ajp
> threads, who are still waiting on the wrong sockets.
> A direct request to Tomcat goes through quickly.
> A request through Apache however, has to wait for one of the stuck ajp
> threads to realise that there is a problem, and build a new connection to
> Tomcat.
> AJP specialists, what's wrong with the above ?
>
> To Jenny : if you were using mod_jk instead of mod_proxy_ajp, then I think
> something like the cping/cpong feature may help you shorten the response
> time.  But I don't know if mod_proxy_ajp has something similar.
>
> I would also in the meantime check if you have the latest version of
> mod_proxy_ajp.  It is a (relatively) recent module, in which a lot of
> changes have happened over the last few months.  Maybe what you are seeing
> is related to something since corrected.
>
>
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