[Mongrel] load balancers and mongrel

Robert Mela rob at robmela.com
Fri Oct 26 21:53:32 EDT 2007

You're coming in just after a discussion about this -- the problem of 
request queuing in Mongrel.   It occurs when a round-robin style load 
balancer cycles back to a Mongrel that still hasn't finished processing 
the request that the load balancer had sent in its previous cycle 
through the pool.

If you're running Apache's mod_proxy_balancer then see this:


and a correction here: 

Andrew Arrow wrote:
> We have a load balancer sending requests to one of X boxes and one of  
> N mongrel processes on that box.
> Since each mongrel processes is multi-threaded but it has a mutex  
> around the section that calls rails, we end up with several requests  
> queued up waiting  when they could have gone to another box with a  
> free process.
> For example, boxA, and boxB.
> boxA has mongrels 1 through 10
> boxB has mongrels 11 through 20
> Load balancer sends a request to boxA mongrel 5.
> Load balancer sends a request to boxB mongrel 12.
> Load balancer sends a request to boxA mongrel 5 again.
> It has to wait for the 1st request still running on boxA mongrel 5.
> How can we help the load balancer know it should have sent the  
> request to any number of other free mongrels vs. queuing up threads  
> that have to wait?
> Thanks.
> _______________________________________________
> Mongrel-users mailing list
> Mongrel-users at rubyforge.org
> http://rubyforge.org/mailman/listinfo/mongrel-users

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