Re: Transaction-controlled robustness for replication

On Tue, 2008-08-12 at 11:52 -0400, Bruce Momjian wrote:
> Simon Riggs wrote:
> > 
> > On Sat, 2008-07-26 at 10:17 +0200, Markus Wanner wrote:
> > > What I still don't understand is, why you are speaking about
> > > "logical" 
> > > replication. It rather sounds like an ordinary log shipping approach, 
> > > where the complete WAL is sent over the wire. Nothing wrong with
> > > that, 
> > > it certainly fits many needs and I welcome such a solution for
> > > Postgres.
> > 
> > Yes, first stage is log shipping. Second stage is either physical or
> > logical apply.
> 
> What is the attraction of logical application of the WAL logs? 
> Transmitting to a server with different architecture?

Yes,

* different release
* different encoding
* different CPU architecture
* (with the correct transform) a different DBMS

So logical apply can provide a route for data transfer between
applications, not just replication for DR or HA.

Physical apply works and will be more performant, but it will always be
more restrictive. So there are arguments for doing it both ways.

I believe that we can and should offer both options to provide customer
choice. Ideally, it would be nice to be able to switch between the two
without significant reconfiguration, but that's definitely not for this
release.

(Pragmatically, implementation will be limited by my funding.)

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support