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From Jess Holle <je...@ptc.com>
Subject Re: mod_proxy/mod_proxy_balancer bug
Date Fri, 17 Apr 2009 21:20:39 GMT
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'd be /_very_ /interested in such a port to mod_proxy_balancer -- in 
2.2.x in my case.  Any help/pointers/assistance would be appreciated.  I 
could apply such a change as a patch to just my version, but I'd be a 
lot more interested in getting 2.2.x as a whole to a better place and 
not having to maintain my own fork of things.

I get a strong impression that others haven't really pushed 
mod_proxy_balancer in this area.

Overall having solid mod_proxy_balancer functionality obviously benefits 
more than just AJP and I like the idea of mod_proxy_ajp.  That said, if 
mod_jk is going to move ahead and mod_proxy_ajp become a backwater at 
some point I'll need to move back to mod_jk, though I'd really want the 
ability to gracefully throttle requests in mod_jk first.  [When mod_jk 
runs out of connections it gives a 503.  mod_proxy can queue up requests 
instead.]

--
Jess Holle


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