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Re: Feature request: new svn_delta_action zero_bytes

From: <philipp.marek_at_bmlv.gv.at>
Date: 2006-03-02 12:23:18 CET

> Ph. Marek wrote:
> > Hello everybody,
> >
> > I have a feature request: I'd like to have a new enum svn_delta_action
> named
> > zero_bytes or something similar, which could be used eg. for sparse files,
> to
> > save time and bandwidth.
> >
> > Is that a bad idea, or shall I create an issue?
> >
> Did you actually see a significant performance problem?
>
> If you have a (new) range of zeroes in the target stream, the delta for
> it should look like this:
>
> new-data "\0"
> target-copy -1 <length of range -1>
Yes, I read that in svn_delta.h.

> You'd get two instructions instead the ideal one, but the zeroed range
> is still run-length encoded in practice.
>
> I fail to see what that has to do with sparse files, though. Are you
> implying that Subversion should create sparse files on the client if
> they're supported? If so, that's entirely independent of the deltas.
What I meant (but probably failed to say :-) is that if there's a special
encoding for zero-byte ranges the client can just lseek() (and create sparse
files) instead of writing many zero bytes.

I know that GNU tar and cp have special code for finding ranges of 0-bytes, but
that's I'd like to encode that distinctly - it's a good documentation, and
makes handling easier.

But I know that it could be encoded in other ways, and possibly the work
involved (and problems with backporting etc.) is too much.

Thank you!

Regards,

Phil

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Received on Thu Mar 2 12:24:34 2006

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