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
well.
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...
