Re: Comments on the fastestmirror plugin

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

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