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From "Ryan Murray" <>
Subject [users@httpd] RE: [Bulk] [users@httpd] Apache 2.2 and proxy_balancer - tcp session pipelining
Date Fri, 11 May 2007 14:46:43 GMT
> -----Original Message-----
> From: Andy Davidson [] 
> Sent: Friday, May 11, 2007 2:53 PM
> To:
> Subject: [Bulk] [users@httpd] Apache 2.2 and proxy_balancer - 
> tcp session pipelining
> Hi,
> I first posted this question to 
> comp.infosystems.www.servers.unix but had no response.
> mod_proxy_balancer is cool - I like this, guys, thank you.
> I want to load balance a number of back-end worker/target 
> servers that host one web application.  This is easy to do :
>          <Proxy balancer://mysite>
>                  Order allow,deny
>                  Allow from all
>                  BalancerMember
>                  BalancerMember
>          </Proxy>
>          ProxyPass /r balancer://mysite/
>          ProxyPassReverse /r balancer://mysite/
> Now, what I want to do this time is configure my reverse 
> proxy server to open several connections to each of the back 
> end worker servers when the proxy starts to my back end hosts 
> so that the tcp session can be pipelined, thus preventing the 
> burden of creating and tearing down tcp sessions on the back 
> end boxes for new visitor requests.
> I found some documentation on the website 
> which seemed to describe what I want to do :
> Parameter Default       Description
> min       0             Minumum number of connections
>                 that will always be open to the backend server.
> However, this doesn't cleanly map on to the balancer model. 
> If I add 'min=4' to the BalancerMember line this is ignored, 
> and if I add the same to the 'ProxyPass' lines, apache does 
> not understand the configuration.
> Anyone thought of a way around this ?  Is it a feature request ?

If you are using the preform MPM you have one server process for each Apache
worker.  Therefore each apache worker opens exactly one connection to the
back end so max per worker always == 1 and your "real max" connections to
the backend <= number of Apache workers.  With the Prefork MPM, I don't
believe there is way to limit the number of Apache workers which will
actually open connections to the backend.

If you want to avoid this issue and limit the conenctions to the backend you
can use the "Worker" MPM which is multithreaded.  In this case the "max" for
the balancer should be respected.

Ryan Murray
managing director

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