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From André Warnier ...@ice-sa.com>
Subject Re: [users@httpd] 503 status seems to get cached - how do I disable caching?
Date Wed, 10 Jun 2009 08:06:06 GMT
Ryan Murray wrote:
> Did you check the timeout on your apache proxy config?  Once apache has detected the
backend is not available it won't retry again until a certain number of seconds (timeout)
has passed.  I pretty sure mod_proxy defaults to 60 seconds, which I usually reduce to get
a quicker recovery when Tomcat is back up.  
> 
I believe indeed that it must be something in that "category".

This is a case where precise terminology is helpful, and the usage of 
words like "caching" is a bit inappropriate, because it tends to orient 
the thinking toward "browser cache" or "page cache" etc..

I have not verified, but intuitively I would tend to think that no HTTP 
caching mechanism (browser, server, mod_cache, proxies, etc..) would 
ever really "cache" error responses, and keep responding the same from 
some cache memory.

But from some overall performance point of view, it would probably make 
sense that once a back-end has been detected as being "in error" or "not 
responding", the front-end server would not just blindly keep flooding 
it with useless requests.

So, to get back to the original issue : if indeed the observed behaviour 
derives from such a timeout on the part of mod_proxy, I would suggest to 
do some thinking about whether it is not better, in a general sense, to 
leave things as they are, at least if this is a system destined to be 
deployed in production. After all, I am sure that if the developers of 
mod_proxy and/or mod_prox_ajp deemed it justified to introduce such a 
timeout, they probably thought hard about it and decided that it was A 
Good Thing.


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