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Re: do away with db/revprops/*/, and a question about 'upgrade' concurrency (was: Re: Does fsfs revprop packing no longer allow usage of traditional backup software?)

From: Daniel Shahaf <danielsh_at_elego.de>
Date: Fri, 1 Jul 2011 21:42:54 +0300

Daniel Shahaf wrote on Fri, Jul 01, 2011 at 21:30:15 +0300:
> Daniel Shahaf wrote on Fri, Jul 01, 2011 at 19:29:50 +0300:
> > Hyrum K Wright wrote on Fri, Jul 01, 2011 at 11:21:58 -0500:
> > > On Fri, Jul 1, 2011 at 8:05 AM, Daniel Shahaf <danielsh_at_elego.de> wrote:
> > > > Hyrum K Wright wrote on Thu, Jun 30, 2011 at 16:33:16 -0500:
> > > >> On Thu, Jun 30, 2011 at 3:27 PM, Peter Samuelson <peter_at_p12n.org> wrote:
> > > >> >
> > > >> > [Ivan Zhakov]
> > > >> >> It should be easy to implement editing revprops without using SQLite:
> > > >> >> in case someone modify revprop non-packed revprop file is created, in
> > > >> >> read operation non-packed revprop file should be considered as more
> > > >> >> up-to-date. In next svnadmin pack operation these non-packed files
> > > >> >> should be merged back to packed one.
> > > >> >
> > > >> > +1.  This would basically mean there's only _one_ code path for writing
> > > >> > revprops, yes?  'svnadmin pack' gets a little more complex, but the
> > > >> > rest of libsvn_fs_fs gets simpler.
> > > >> >
> > > >> > Anyone have time to actually do this?  Converting the packed format
> > > >> > from sqlite to the same format used for packed revs would be a bonus.
> > > >>
> > > >> I like this idea, but it would seem to introduce an additional stat()
> > > >> call* for every attempt to fetch a revprop, because you'd first have
> > > >> to check the "old" location, and then the packed one.
> > > >
> > > > I don't like the idea of writing revprops outside the DB and moving them
> > > > back in. (I think I already said why elsethread?)
> > >
> > > (I will assume "the DB" means "the SQLite-backed revprop database".)
> > >
> > > I agree with you, but I don't think that's what the proposal was
> > > about. My understanding would be that we'd pack revprops just like we
> > > pack revision (one single concat'd file per shard), and then store any
> > > edits in separate files. We'd then "repack" the edits into the pack
> > > files when an admin subsequently runs 'svnadmin pack'.
> >
> > Yes, that's exactly what I don't like :-)
>
> I take that back --- what Hyrum described here is not the same as my
> previous understanding.
>
> How about storing just a single serialized hash per shard, but
> nameprefix the properties?

By the way --- I realize that I haven't yet expressed on an opinion on
the suggestion as described by Hyrum --- I am simply still trying to see
if I can find a race condition in there. (My previous example will fail
if the 'separate files' are stored at a path other than revprops/0/42.)
Received on 2011-07-01 20:43:49 CEST

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