From: | Josh Berkus <josh(at)agliodbs(dot)com> |
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To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: [PATCH 8/8] Introduce wal decoding via catalog timetravel |
Date: | 2012-10-11 22:27:27 |
Message-ID: | 507747CF.7040301@agliodbs.com |
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Thread: | |
Lists: | pgsql-hackers |
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
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