Rainer, do you want to have a go at this one ?
-------- Original Message --------
Subject: Re: [us...@httpd] 503 status seems to get cached - how do I
disable caching?
Date: Tue, 9 Jun 2009 15:37:25 -0500
From: Jenny Brown <skyw...@gmail.com>
Reply-To: us...@httpd.apache.org
To: us...@httpd.apache.org
References:
<ffb3a35a0906080938i1d9b5c8do7fa781a9e1658...@mail.gmail.com>
<4a2d45fd.8050...@ice-sa.com>
<ffb3a35a0906081050u40fe7c45h66b4a07acccab...@mail.gmail.com>
<ffb3a35a0906081053r1b8d020ds4b34be060276...@mail.gmail.com>
<4a2d54d7.7020...@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<a...@ice-sa.com> wrote:
Jenny Brown wrote:
On Mon, Jun 8, 2009 at 12:50 PM, Jenny Brown<skyw...@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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