Re: [RFC][PATCH] wal decoding, attempt #2 - Design Documents (really attached) - Mailing list pgsql-hackers

On 15 October 2012 19:19, Bruce Momjian <bruce@momjian.us> wrote:
> I think Robert is right that if Slony can't use the API, it is unlikely
> any other replication system could use it.

I don't accept that. Clearly there is a circular dependency, and
someone has to go first - why should the Slony guys invest in adopting
this technology if it is going to necessitate using a forked Postgres
with an uncertain future? That would be (with respect to the Slony
guys) a commercial risk that is fairly heavily concentrated with
Afilias. So, if you're going to attach as a condition to its
acceptance that the Slony guys be able to use it immediately (because
"can integrate" really means "will integrate", right?), you're
attaching it to a rather arbitrary condition that has nothing much to
do with the technical merit of the patches proposed. The fact of the
matter is that Slony was originally designed with a somewhat different
set of constraints to those that exist today, so I don't doubt that
this is something that they're going to need to integrate over time,
probably in a separate release branch, to get the upsides of in-core
logical replication, along with the great flexibility that Slony
currently offers (and that Afilias undoubtedly depend upon today).

Another way of putting this is that Postgres should go first because
we will get huge benefits even if only one of the trigger-based
logical replication systems adopts the technology. Though I hope and
expect that the Slony guys will be able to work with what we're doing,
surely a logical replication system with all the benefits implied by
being logical, but with with only some subset of Slony's functionality
is still going to be of great benefit.

My view is that the only reasonable approach is to build something
solid, well-integrated and generic, in core. I'd certainly like to
hear what the Slony guys have to say here, though.

-- 
Peter Geoghegan       http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services