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Re: Is FSFS compressing stored data?

From: Garrett Rooney <rooneg_at_electricjellyfish.net>
Date: 2004-10-14 14:38:39 CEST

Scott Palmer wrote:
>
> On Oct 13, 2004, at 8:05 PM, Greg Hudson wrote:
>
>>> They both compress. The reasons BDB is bigger are complex, and have
>>> to do with how databases allocate storage.
>>
>>
>> Er, no, BDB stores the head revision in uncompressed plaintext,
>> whereas FSFS stores all file revisions as deltas against something.
>> (The first rev of a file is stored as a delta against empty.)
>>
>
> How does FSFS store the HEAD revision then? If it needs to process
> deltas to get the HEAD revision that would lead to performance problems
> would it not? I was under the impression that the usually way to store
> versions is to use reverse deltas from the HEAD revision to get the
> older revision, so generally the HEAD revision is stored verbatim (as
> you say it is for BDB).

It uses skip deltas, so it only needs to apply at most log(n) deltas to
get to any given revision. It's a little bit slower, but not noticable
in my experience.

-garrett

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Received on Thu Oct 14 14:39:07 2004

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