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RE: Discontinuing the use of SVN.

From: Dale Worley <dworley_at_pingtel.com>
Date: 2005-06-06 18:00:29 CEST

> From: Ben Collins-Sussman [mailto:sussman@collab.net]
>
> > After much frustration (and yelling) I have been told to remove SVN
> > from our production pipeline after the latest round of ‘Checksum
> > mismatch’ errors.
>
> Sorry about that. The checksums exist to point out hardware
> problems
> with network, disk, and memory. I hope your hardware is okay!

I used to get these messages regularly. I never really tracked them down,
but eventually it became clear that the central problem was that I was
maintining two copies of the WC on two machines and using Unison to keep
them in sync. In theory, this isn't a problem if you maintain discipline,
only use one WC at a time, and do a re-sync whenever you change your
attention from one WC to the other. But in practice, you forget to do that,
and Unison can only partially propagate the changes.

As far as I know, all instances of "Checksum mismatch" were when my
text-base file contained a different version than the entries file said it
was. There were also some other times when empty-file got deleted. (I
don't know why.)

What was particularly annoying about these situations was that they were, in
theory, quite mendable -- a program could easily have detected the incorrect
text-base files and queried the repository for the correct versions. (This
is a consequence of the fact that the text-base is just a cache.) Sometimes
I did this manually, and it worked as expected.

Eventually I stopped using the synchronized-WCs methodology, so I never got
motived to write the WC-cleaning script.

Dale

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Received on Mon Jun 6 18:32:36 2005

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