Jan Wieck <JanWieck at Yahoo.com> writes:
> On 7/3/2007 12:33 PM, Christopher Browne wrote:
>> "Andrew Hammond" <andrew.george.hammond at gmail.com> writes:
>
>>> Also, ISTM that the big reason we don't like statement based
>>> replication is that SQL has many non-deterministic aspects. However,
>>> there is probably a pretty darn big subset of SQL which is provably
>>> non-deterministic. And for that subset, would it be any less
>>> rigorous to transmit those statements than to transmit the per-row
>>> change statments like we currently do?
>> Well, by capturing the values, we have captured a deterministic form
>> of the update.
>
> How to figure out what is deterministic and what isn't? A simple
>
>     insert into summary select id, sum(value) from detail group by id;
>
> seems pretty deterministic, doesn't it? But the result of it depends
> on the exact commit order and the transaction isolation level. We
> don't capture the commit order of single transactions, nor do we care
> for it anywhere in the Slony-I logic.

But at the time that we apply these changes in log_actionseq order, we
have imposed a deterministic order.  (Which happens to be repeatable,
on each node.)
-- 
"cbbrowne","@","linuxfinances.info"
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