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Re: [Gluster-devel] Client side AFR race conditions?

From: Martin Fick
Subject: Re: [Gluster-devel] Client side AFR race conditions?
Date: Thu, 1 May 2008 15:16:22 -0700 (PDT)

--- Gordan Bobic <address@hidden> wrote:

> Martin Fick wrote:
> > I am curious, is client side AFR susceptible to
> race
> > conditions on writes?  If not, how is this
> mitigated? 
> > 
> > 
> > In other words, what prevents conflicts when
> client A
> > & B both write to the same file?  Could A's write
> to
> > subvolume A succeed before B's write to subvolume
> A,
> > and at the same time B's write to subvolume B
> succeed
> > before A's write to subvolume B?  If so, isn't
> this
> > somewhat similar to a split brain operation?  Is
> there
> > some form a transaction layer using file version
> #s
> > that prevents this?
> I would imagine the same thing happens as would
> happen on a local FS.

Well, it can't happen on a local FS.  On a local FS
one of the clients would win.  While you may not know
which one will win, with the scenario I am describing
they both win but on different subvolumes.  This would
leave subvolume A with client B having won and
subvolume B with client A having won.  Now depending
on which subvolume I read from I will get a different
answer.  With a local FS I can only get one answer. 
Does that make sense?


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