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Re: why the change in the checksums

From: Greg Stein <gstein_at_lyra.org>
Date: 2003-02-03 08:50:13 CET

On Sun, Feb 02, 2003 at 08:20:47PM -0500, mark benedetto king wrote:
> On Sun, Feb 02, 2003 at 08:36:37AM -0800, solo turn wrote:
> > does somebody know why exactly the "checksumming, more checksumming"
> > was introduced?
> >
> We've seen network data corruption. Correct IP checksums, incorrect
> data. It's bound to happen: 16 bits of checksum is just not enough.
> Maybe that's okay for web-surfing, but it's not okay for svn. Application
> level data integrity checking is a requirement.

Yup. There are any number of avenues for corruption which are totally
outside of our control (bad RAM, bad disk, etc). It does and it will happen.
And Subversion can now detect it.

I think ben understates a key point: a version control system simply CANNOT
lose data. Trust is paramount. Checksums are one way to watch out (or at
least, detect) corruption. One day, Subversion will goof, and we'll be happy
for those checksums.

[ I tell ya, though... we're already well ahead of systems like SourceSafe
  or ClearCase, where all the logic is on the client side; any tweaky thing
  on the client or the network... blam. admins specifically run procedures
  to watch for and deal with corruption in those systems ]


Greg Stein, http://www.lyra.org/
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Received on Mon Feb 3 08:47:21 2003

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