Slony uses the pgsql protocol for inter-node communication.  I can
attest to success with IPSec VPN compatibility from a Major Vendor.  You
just need to plan your WAN bandwidth needs accordingly.  Check out
"Metro Ethernet" technology for metro-area networks.
 

On Wed, 2007-06-27 at 16:05 -0400, Christopher Browne wrote:
> Andrew Sullivan <ajs at crankycanuck.ca> writes:
> > On Wed, Jun 27, 2007 at 10:12:31AM +0800, Dewi Andriyanti wrote:
> >> I intend to build a replication system via VPN using Slony but I need more
> >> reference. Is Slony good in data integrity, consistency, reliability and
> >> response time? Is Slony better than PGCluster? What is drawbacks of Slony?
> >> Would anybody help me to share stable configuration for replication system
> >> via VPN using Slony?
> >
> > What's the bandwidth available inside the VPN?  You need to make sure
> > you can propagate the changes fast enough.  I don't believe PGCluster
> > can work over wide areas -- I think it has to be local.
> 
> I haven't seen any discussion of PGCluster in a while; the thing that
> has been discussed a lot more of late has been PGCluster-2.
> 
> That's a system which shares parts of PostgreSQL shared memory across
> the network; I would expect that to perform extraordinarily badly
> across a WAN.  If PGCluster uses a similar architecture, then the same
> would presumably be true.  I'm not sure they are identical that way,
> though...