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Re: fsfs revprop packing in f5 Re: Does fsfs revprop packing no longer allow usage of traditional backup software?

From: Peter Samuelson <peter_at_p12n.org>
Date: Thu, 7 Jul 2011 12:22:11 -0500

[Hyrum K Wright]
> I've created the revprop-packing branch to do the implementation. It
> currently has a skeleton BRANCH-README, which Daniel will be
> augmenting shortly.

This might open another small can o' worms, but "while we're already
bumping the format and rewriting the content...": each revprops blob
should include its rev number, length, and checksum, prepended to the
blob itself. (Or if it's awkward to prepend a checksum, put those
things at the end, and omit the length as it is redundant by then.)
This gives us just that much more for 'svnadmin verify' to verify, and
that's a Good Thing. It is also insurance of a sort, to make it easier
to implement things like rewriting a revprops entry _in situ_ when the
new is not larger than the old (including, perhaps, a bit of padding).
A reader that encounters a bad checksum could just pause, retry, and
only throw an error if the wrong checksum persists too long. Also,
this removes the write barrier requirements between the content and the
manifest, even if we only append edited entries.

Peter Samuelson | org-tld!p12n!peter | http://p12n.org/
Received on 2011-07-07 19:22:47 CEST

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