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Re: Reconstructing a file on checkout and SVN scaling

From: Brad O'Hearne <brado_at_neurofire.com>
Date: 2005-03-23 15:45:58 CET

Thanks! This helped tremendously!


Garrett Rooney wrote:

> Brad O'Hearne wrote:
>> After reading the documentation that generally describes how files in
>> SVN are stored (by storing diffs and references to previous
>> versions), and after doing some poking around in the files created in
>> a filesystem-type repository, I've begun wondering about how SVN
>> scales. Suppose I have a file added to subversion at revision 1, and
>> it is changed 5000 times, with each change committed individually.
>> When I checkout revision 5001 of that file from subversion, does
>> subversion have to reconstruct this file by examining every change in
>> sequence from revision 1? Will this result in a substantially
>> increased checkout time to reconstruct this file to its proper revision?
>> There is obviously a question aimed at scaling. In a large system, if
>> the above scenario is true, there exists the possibility of coming to
>> a grinding halt with many files changed over many revisions. Merely
>> checking out a project would be a fairly intensive operation.
>> I'm sure I am missing something. I was hoping some of the svn gurus
>> out there could educate me as to how subversion handles this.
> Depending on which back end filesystem you're using the answer is
> different. In a BDB based filesystem the HEAD revision (most recent
> version) is stored as fulltext, since that's what you usually want to
> see, and deltas are applied only when you need previous revisions. In
> an FSFS based repository you do indeed have to start at the initial
> version and apply deltas forward, but the deltas are stored in such a
> way so as to only require applying of log(n) deltas to get to any
> given version of a file. See
> http://svn.collab.net/repos/svn/trunk/notes/skip-deltas for detailed
> notes on how the FSFS version of this works.
> -garrett

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Received on Wed Mar 23 15:48:34 2005

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