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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: mod_jk/1.2.32 - Error connecting to Tomcat only on one page
Date Fri, 21 Sep 2012 21:45:55 GMT
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Nicholas,

On 9/21/12 4:14 AM, Nicolas Sarazin wrote:
> Ok for all versions upgrades, I put it in my todo list ! It is a 
> customer environment, I can't make it immediately.

That's okay, but you need to be ready when your customer says "hey,
Tomcat 5.5.x is no longer supported: we need to upgrade".

>> Christopher Schultz wrote:
>> 
>> Do you have anything else? If not, why bother with Apache httpd?
> 
> Yes, we have lot of directives (using mod_cache, mod_proxy, ...).
> In reality, I have about twenty VirtualHost.

Fair enough: it's always worth asking. Lots of people think that
Apache httpd is, for some reason, required.

>> What MPM are you using? If you are using prefork, then your 
>> connection_pool_size is all wrong. Generally speaking, you
>> should allow mod_jk to determine its own value for
>> connection_pool_size when using Apache httpd.
>> 
>> How many backend Tomcat servers do you have? Looks like one.
>> 
>> Let's assume you are using threaded MPM in httpd (otherwise the
>> value for 1200 is insane) and you are using only one backend
>> Tomcat server.
>> 
>> You have 1200 connections configured in httpd
>> (connection_pool_size), but Tomcat can only accept 600 of them
>> (maxThreads) at any given time. You have used backlog=8192 to
>> cover this up so things become even more confusing.
> 
> I using prefork. Indeed, in Apache documentation : "Do not use 
> connection_pool_size with values higher then 1 on Apache 2.x
> prefork or Apache 1.3.x!". It's better to delete it or to put its
> value to 1 ?

I would delete the option altogether - per the documentation - and
allow mod_jk to select the appropriate setting.

> What problems can arise with mpm prefork and connection_pool_size >
> 1 ?

A big waste of memory and a lot of needless overhead. I dunno how
mod_jk manages its connections, but it might immediately open 1200
connections per prefork process to your backend, which can waste a lot
of resources, too.

>>> Usually, it's work correctly, but sometime, only on certain
>>> pages, woker can't connect to Tomcat. In my logs files, I have
>>> :
>> 
>> I think it's only a coincidence that /page2 consistently gives
>> you 500-response errors, here. Try looking at a wider section of
>> your httpd access log to determine if there really is something
>> special about /page2 (of course, /page2 could be returning
>> 500-response itself: you might want to check on that).
> 
> This page was in error 500 in acces log between 19:12:27 and
> 20:04:39.
> 
>>> How can we explain this behavior ?
>> 
>> There are lots of explanations for what you are seeing.
>> 
>> A few questions:
>> 
>> 1. Do you really need Apache httpd at all? 2. Can you configure
>> cping/cpong for connection liveness testing? 3. Have you tried
>> disabling AJP connection re-use altogether? localhost
>> communication is fast fast fast.
> 
> 1 - Yes :) 2 - Yes, but not immediately 3 - I don't, but I am going
> to test !

Good luck.

- -chris
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