Re: [PATCH 8/8] Introduce wal decoding via catalog timetravel

On 10/10/12 7:26 PM, Bruce Momjian wrote:
> How does Slony write its changes without causing serialization replay
> conflicts?

Since nobody from the Slony team answered this:

a) Slony replicates *rows*, not *statements*
b) Slony uses serializable mode internally for row replication
c) it's possible (though difficult) for creative usage to get Slony into
a deadlock situation

FWIW, I have always assumed that is is impossible (even theoretically)
to have statement-based replication without some constraints on the
statements you can run, or some replication failures. I think we should
expect 9.3's logical replication out-the-gate to have some issues and
impose constraints on users, and improve with time but never be perfect.

The design Andres and Simon have advanced already eliminates a lot of
the common failure cases (now(), random(), nextval()) suffered by pgPool
and similar tools. But remember, this feature doesn't have to be
*perfect*, it just has to be *better* than the alternatives.

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com