On Wed, Aug 10, 2016 at 12:26 PM, Greg Stark <st...@mit.edu> wrote:

> Complexity like this makes it hard to implement other features such as
> CSNs. IIRC this already bit hot standby as well. I think it would be a
> big improvement if we had a clear, well defined commit order that was
> easy to explain and easy to reason about when new changes are being
> made.

And here I was getting concerned that there was no mention of
"apparent order of execution" for serializable transactions --
which does not necessarily match either the order of LSNs from
commit records nor CSNs.  The order in which transactions become
visible is clearly a large factor in determining AOoE, but it is
secondary to looking at whether a transaction modified data based
on reading the "before" image of a data set modified by a
concurrent transaction.

I still think that our best bet for avoiding anomalies when using
logical replication in complex environments is for logical
replication to apply transactions in apparent order of execution.

Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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