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From Jim Jagielski <>
Subject Re: mod_proxy/mod_proxy_balancer bug
Date Mon, 20 Apr 2009 13:57:04 GMT

On Apr 17, 2009, at 4:28 PM, Rainer Jung wrote:
> The same type of balancing decision algorithm was part of mod_jk  
> between
> 1.2.7 and 1.2.15. I always had problems to understand, how it exactly
> behaves in case some workers are out of order. The algorithm is
> interesting, but I found it very hard to model its mathematics into
> formulas.
> We finally decided to switch to something else. For request, traffic  
> or
> session based balancing we do count items (requests, bytes or new
> sessions), and divide the counters by two once a minute. That way load
> that happened in the past does count less.
> Furthermore a worker that was dead or deactivated some time gets the
> biggest current load number when being reactivated, so that it  
> starts a
> smooth as possible.
> I expect porting this to mod_proxy in trunk will be easy, but I'm not
> sure what experience others have with the fairness of balancing in  
> case
> you add dynamics to the workers (errors and administrative downtimes).

I have some ideas on the "soft start" when a errored-out worker
returns (or when a new worker is added *hint* *hint*) that I've
been playing with. The main thing, for me at least, is low overhead,
even if it means sacrificing accuracy to the nth decimal place...
I used to think aging was not something we wanted to do in
mod_proxy, but mostly it was based on complex aging, and the
overhead associated with that. But I have some ideas there as

The main thing I've been working on is trying to do all these
things in trunk in a way that is "easily" backportable to 2.2...

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