Re: Clustering features for upcoming developer meeting -- please claim yours!

On 5/10/2010 4:25 PM, Marko Kreen wrote:
> AFAICS the "agreeable order" should take care of positioning:
>
>   http://wiki.postgresql.org/wiki/ModificationTriggerGDQ#Suggestions_for_Implementation
>
> This combined with DML triggers that react to invalidate events (like
> PgQ ones) should already work fine?
>
> Are there situations where such setup fails?
>

That explanation of an agreeable order only solves the problems of
placing the DDL into the replication stream between transactions,
possibly done by multiple clients.

It does in no way address the problem of one single client executing a
couple of updates, modifies the object, then continues with updates. In
this case, there isn't even a transaction boundary at which the DDL
happened on the master. And this one transaction could indeed alter the
object several times.

This means that a generalized data queue needs to have hooks, so that
DDL triggers can inject their payload into it.


Jan

--
Anyone who trades liberty for security deserves neither
liberty nor security. -- Benjamin Franklin