Anybody interested in testing patch to allow weighted nodes?

Brad Fitzpatrick brad at
Thu May 17 05:52:46 UTC 2007

On Wed, 16 May 2007, Brett G. Durrett wrote:

> Yeah, you're right... I think people will probably expect what you
> expected, a per-request weight.  I should have been more clear about the
> "weighting" mechanism.  Like I said, my preference would be on a per
> request weight but this was a quick hack that looks like it meets our
> specific needs.
> To get more feedback and possibly influence a revised patch... I assume
> people are achieving weighting by limiting the connections at the web
> server level... does this just work for everybody or is there a
> preference for controlling the weighting via perlbal?  Controlling
> weighting at the load balancer level seems like a common expectation
> (granted, with a per-request level of control) but maybe I am thinking
> about this the wrong way.
> So my question to this mailing list is...  does the perlbal community
> see any value in having a weighting mechanism?  If the answer is no, I
> would love to hear how you are achieving the same effect and why your
> solution is your preferred mechanism.

In my experience, people think they want a weighting mechanism, but they
really, really don't.  The load balancer can be much smarter and quicker
to adapt than any human adjusting weights.

Especially modern web apps with widely-varying response times.  Perhaps in
the past with all backend nodes serving the same 3 static files, then
statically-defined weighted load balancing might make sense... but still
not really.

I'd need a great reason to include such a feature.

That said, an upcoming change to Perlbal will make weighted requests to
backends a lot easier to implement properly, but I might still fight it,
or at least make it really hard to enable on accident.

- Brad

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