On Mar 4, 2008, at 6:34 AM, Poul-Henning Kamp wrote: > In message <[EMAIL PROTECTED]>, Shiraz Kanga writes: >> >> Will it be possible to implement custom Load Balancing algorithms in >> VCL? There are numerous algorithms that can be used to distribute >> load like >> Round Robin, Weighted Round Robin, Least Connections, Fastest >> Response, >> Most Bandwidth, etc. > > The plan is to implement such "directors" in C (we already have > "random") > and I'm not convinced that doing it in VCL makes much sense, but can > be persuaded otherwise by good arguments.
Load balancing algorithms can be complicated over larger sets of backends (if that is the desired use case). mod_backhand was written specifically as a platform to test different algorithms in the lab. What I learned from that is that if you have a good (and very simple) API to implement new algorithms, then it is easy enough to test. For example, we found interesting and successful approaches using cost- benefit-based algorithms and randomized-log2-window algorithms (much better than simple random). As a note, simple random performs really well in the lab (better than least-connections and fastest-response) and in practice, while it doesn't do as well, it still does better than most alternatives -- so good first algorithm selection. On the other hand, VCL compiles to C. It seems you have an excellent platform to expose that algorithm composition up the stack and make it even more accessible without compromising efficiency. At the end of the day, it would only be a convenience thing. If not in VCL, I hope that it could be at least dlopened, so algorithms can be tested post- install. Best regards, Theo -- Theo Schlossnagle Esoteric Curio -- http://lethargy.org/ OmniTI Computer Consulting, Inc. -- http://omniti.com/ _______________________________________________ varnish-dev mailing list varnish-dev@projects.linpro.no http://projects.linpro.no/mailman/listinfo/varnish-dev
