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Re: Bug#641769: [apt] fetches InRelease file, problematic on several mirrors (aka "Packages Hash Sum mismatch")

Le 2011-09-17 11:34, Henrique de Moraes Holschuh a écrit :
retitle 636292 dak/apt: deficiencies at handling out-of-sync metadata
summary 636292 87

If anyone disagrees with the above triage, please change the summary
and/or title.  Thank you.

On Sat, 17 Sep 2011, Filipus Klutiero wrote:
#636292 is labelled as being about round-robin mirrors and problems
APT has with those, even though that is probably not the actual
cause of the reporter's problem.
You're expected to read the entire thing when refered to a bug report in
a thread you're replying to.
I was unaware of that.

But indeed, there would be room for a general bug "unreliable
package indices fetching protocol" :-S
That misses the point, IMO.  To me, it looks like what's "broken" is
that the repository format _and_ the front-ends have deficiencies at
handling metadata which is unsyncronized either in-mirror or across
mirrors.  And these deficiencies are a lot more important nowadays than
they once were, as we have now many dinstall runs per day, lots of users
tracking testing and unstable, a larger set of metadata files, a larger
and more diverse set of mirrors... I.e: a lot more chances to hit
unsyncronized metadata windows.

I don't think increasing dinstall frequency worsens these issues significantly if dinstalls get shorter (unless previous dinstalls ran during the night). I also think archive size growth should have been compensated by performance increases. I think the time spent synchronizing a mirror must not have increased a lot. What did change here (dramatically) is the proportion of that time where APT indices updates fail. Round-robin mirrors might also have worsened.

Anyway, the repository format is not a problem per se, it's the combination of what's on a mirror and how APT fetches it that's a problem. If you assume the communication protocol is HTTP-like, then indeed there should be mechanisms to cope with race conditions - i.e. file versioning and/or having APT retry or report desynchronizations.

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