Re: cluster replication with intermezzo

Neil Conway wrote:
>
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> > Robert Williams <bob(at)bob(dot)usuhs(dot)mil> writes:
> > > I don't thing this should be a problem,
> > > since as I understand it, table and row
> > > locking occurs at the postgres backend level
> > > and lock files are kept in a database table,
> >
> > No, the locking is all done in shared memory. Since you've got two
> > postmasters with two separate shared memory blocks, there is no
> > interlocking between the two sets of backends.
>
> Speaking of which, I vaguely recall the OpenMOSIX guys talking about
> possibly implementing clusterable shared memory (i.e. "shared" across
> machines in a cluster) at some point in the future. There would still
> be some problems with using PostgreSQL in that environment (e.g. the
> different semantics between NFS and normal filesystems), but it's an
> interesting possibility, at any rate.

Only if they implement cluster-shared-memory supporting TAS. Otherwise
we would have to fallback to some sort of cluster-safe implementation of
semaphores for every single bit to lock ... and that I guess would eat
alot of the neat performance someone expects to get from that setup.

Jan

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