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AW: Balancing and proxing

From: Markus Schaber <m.schaber_at_codesys.com>
Date: Mon, 12 Aug 2013 07:08:52 +0000

Hi, Roman,

Von: Roman Naumenko [mailto:roman_at_naumenko.ca]
> Ryan Schmidt said the following, on 09-08-13 9:15 PM:
> [....]
> >> But more important, I'd like to have a few nodes handling writes.
> >>
> >> Ah yes. Well then that's different.
> >>
> >> You must have one heck of a large svn installation for that to be a
> bottleneck.
> One day it might grow there, but even with the moderate load it is still a
> huge convenience when pair or more frontends available to handle the load,
> can take one down for maintenance any time. VMs can be used instead of
> physical box too and sized more adequately.
> Of course, it would be ideal if subversion nodes could just share a storage,
> so any sort of requests from a load balancer can processed by any node
> without need to replicate changes over network.

If you use a shared storage which provides working locking semantics, exactly this is possible.

SVN already supports several processes accessing the same repository (like the mod_dav_SVN processes in an apache multiprocess configuration, svnserve (directly and via svn+ssh), and local file:// access), even different versions if they all support the given repository version.

So if your file system guarantees working semantics for locking, using a shared data storage should work.

> > I have not set it up myself, but I participated in discussions about it on
> this list some years ago:
> >
> > http://svn.haxx.se/users/archive-2006-10/0195.shtml
> >
> > http://svn.haxx.se/users/archive-2007-05/0214.shtml
> >
> > You may want to read those threads completely and carefully to get all the
> nuances. And of course information may have changed since then.
> Tom Mornini <tmornini_at_engineyard.com> confirmed that GFS works in that
> thread and the other too, http://svn.haxx.se/users/archive-2007-01/1307.shtml
> But again, there is no "official" confirmation or reference architecture.
> It seems like the number of repositories or the load on a server is never
> large enough to make administrators (or subversion developers to some extent)
> designing or implementing load-balancing cluster. Or maybe it is close to
> huge, but in most cases svnsycn + write-though solve the problem.
> On the other side, there are commercial solutions available, so demand must
> be there :)

Subversion is a free software project, and "everyone has its own itch to scratch". :-)

The demand is there, and there are solutions (whether using shared storage, or the built-in transparent proxy mode of mod_dav_svn, or WanDiscos proprietary solution).

For example, apache.org hosts hundreds of projects (including SVN itself) and more than 1.5 million revisions using the built-in transparent write-through proxy mode.

While Subversion as a free software project may not seem to "officially confirm" some of those solutions, the SVN community also is "just" a group of volunteers who share some common stakes in the SVN development, and not a commercial IT support offering.

On the other hand, installations of the scale you envision should always be backed by professional SVN support. If you don't have the knowledge in-house, I suggest you sign a support contract with one of the companies providing commercial SVN support, preferably one of those who hired some of the committers, as those companies will then provide support and "official confirmation" for whatever setup they conceptualize for your problem.

Best regards

Markus Schaber

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Received on 2013-08-12 09:09:40 CEST

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