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Re: svnadmin dump: deleted file order differs between original & mirrored repos

From: Dustin Lang <dstn_at_astro.princeton.edu>
Date: Mon, 28 May 2012 16:41:59 -0400 (EDT)

D'oh, I didn't RTFIssues. My apologies.
   http://subversion.tigris.org/issues/show_bug.cgi?id=4134

--dstn

On Mon, 28 May 2012, Dustin Lang wrote:

>
> Hi,
>
> For backup purposes I keep a mirror of my svn repo. The mirror is modified
> only by "svnsync", which runs hourly in a cron job.
>
> In order to validate the mirror, I run an "svnadmin dump" on the mirror and
> on the original, and assert that their md5sums are the same.
>
> I am finding that in a few of the revisions in my history, in which a set of
> files are deleted, the svndumps on the original & mirrored repos will list
> the files in different orders, which of course makes the md5sums different
> even though the repos appear to be in the same state.
>
> Both the original & mirror are fsfs-format, and I'm using subversion-1.7.1 on
> both sides. (I just checked that subversion-1.7.5 does the same thing.) The
> apr and other libs are likely different versions, though.
>
> I tried to create a small test repo that demonstrates this behavior, but I
> haven't been able to trigger it. Argh. I've been running this backup
> approach for a long time and never seen this before, but it does show up in a
> few revs in my repo. (The repo is available at http://astrometry.net/svn,
> and rev 20053 shows this behavior, FWIW)
>
> I added some debugging output to subversion/libsvn_delta/path_driver.c :
> svn_delta_path_driver() and it does visit the deleted files in the same
> order, but my guess is that since the deleted files get added to a hash
> (subversion/libsvn_repos/dump.c : delete_entry(), pb->deleted_entries) and
> then the hash gets iterated over later, in close_directory()), maybe the
> order of hashkeys isn't defined, so the order they actually get written out
> can vary. But I've spent a total of maybe 15 minutes working with the
> subversionn/apr code so your guess is better than mine.
>
> Suggestions on how to proceed would be appreciated. My first guess would be
> to sort the deleted entries in close_directory() before writing them out, or
> use a list-like rather than hash-like data structure to store the delete
> entries.
>
> cheers,
> dustin
>
>
>
> Background: the dump is something like:
>
> ${SVNADMIN} dump -q --incremental -r 20000:HEAD ${MIRROR} | \
> grep -v Text-copy-source-md5 | \
> md5sum -
>
> And I do the same on the remote side via ssh. The 20000 is there to make it
> run faster; I keep archives of the svndumps up to 20k.
>
> (This does mean that if there is a change to the original repo between the
> svnsync and the svndump, the md5sums will come out different. This is a
> low-traffic repo so I actually like the occasional false alarm: if your smoke
> alarm goes off when you burn toast, at least you know it still works.)
>
Received on 2012-05-30 02:11:58 CEST

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