Comments on the fastestmirror plugin

[Patrick O'Callaghan]

On Sat, 2010-03-13 at 16:52 -0500, Bill Davidsen wrote:
> Patrick O'Callaghan wrote:
> > The yum fastestmirror plugin (yum-plugin-fastestmirror) claims to
> > evaluate the speed of a bunch of repo mirrors and use the fastest one
> > relative to the user's location.
> > 
> > However AFAIK what it *actually* does is make a test connection to the
> > to the candidate mirrors and order them according to response time,
> > which in many cases is dominated by network latency, which can distort
> > the results. For well-connected user machines in first-world countries
> > it probably doesn't matter much, and may have the beneficial effect of
> > spreading the load over a wider range of mirrors, but for those of us in
> > a less privileged position it can matter a lot. Ironically, these are
> > the cases where such an optimization could do the most good.
> > 
> And there you have the heart of the problem, the evaluation is not remotely 
> correct for most cases. It would be worth adding code to download some small RPM 
> from a number of sites and measure b/w for something real. However, disabling 
> the feature works, too.

Sadly, downloading a "small" RPM is unlikely to give very reliable
results either. Due to TCP slow-start, a stable effective b/w may only
be reached after some 10's of kb have been downloaded.

This is not an easy problem to solve.

poc