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

On Mon, Oct 15, 2012 at 09:57:19AM +0200, Andres Freund wrote:
> On Monday, October 15, 2012 04:54:20 AM Robert Haas wrote:
> > On Thu, Oct 11, 2012 at 3:15 AM, Heikki Linnakangas
> >
> > <hlinnakangas(at)vmware(dot)com> wrote:
> > > IMHO that's a good thing, and I'd hope this new logical replication to
> > > live outside core as well, as much as possible. But whether or not
> > > something is in core is just a political decision, not a reason to
> > > implement something new.
> > >
> > > If the only meaningful advantage is reducing the amount of WAL written, I
> > > can't help thinking that we should just try to address that in the
> > > existing solutions, even if it seems "easy to solve at a first glance,
> > > but a solution not using a normal transactional table for its log/queue
> > > has to solve a lot of problems", as the document says. Sorry to be a
> > > naysayer, but I'm pretty scared of all the new code and complexity these
> > > patches bring into core.
>
> > I do not personally believe that a WAL decoding solution adequate to
> > drive logical replication can live outside of core, at least not
> > unless core exposes a whole lot more interface than we do now, and
> > probably not even then. Even if it could, I don't see the case for
> > making every replication solution reinvent that wheel. It's a big
> > wheel to be reinventing, and everyone needs pretty much the same
> > thing.
> Unsurprisingly I aggree.
>
> > That having been said, I have to agree that the people working on this
> > project seem to be wearing rose-colored glasses when it comes to the
> > difficulty of implementing a full-fledged solution in core.
> That very well might be true. Sometimes rose-colored glasses can be quite
> productive in getting something started...
>
> Note at this point were only want wal decoding, background workers and related
> things to get integrated...

Well, TODO does have:

Move pgfoundry's xlogdump to /contrib and have it rely more closely on
the WAL backend code

I think Robert is right that if Slony can't use the API, it is unlikely
any other replication system could use it.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +