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Re: Solving the compression dilema when rsync-ing Debian versions

On 14 Jan 2001, Richard Atterer <deb-devel@list.atterer.net> wrote:

> Ah, the magic rolling checksum value is the "missing link"!
> But I'm surprised that the value 0, one out of 2^32 possible Adler32
> checksum values, appears so often in typical data to make the scheme
> work?! Seems like Adler32 isn't so strong a checksum after all. :-/
> BTW, 0 is the Adler32 of an all-zeroes area - if the uncompressed data
> contains long runs of zero, there will be *lots* of flushes unless
> special action is taken.

My understanding is that the checksum is truncated from 32 to n bits,
which allows you to tune the probability of hitting the magic value
and therefore the tradeoff between compression and rsyncability (tm).  I don't think the 

Martin Pool, Linuxcare, Inc.
+61 2 6262 8990
mbp@linuxcare.com, http://www.linuxcare.com/
Linuxcare. Support for the revolution.

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