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

On 5/10/2010 1:39 PM, Josh Berkus wrote:
> Jan,
>
>> Aside from that list, I'd like to get into a little more detail on DDL
>> triggers. This seems to be something I could actually work on in the
>> future.
>
> Is this the same thing as the general modification trigger?

To my understanding, the general modification triggers are meant to
unify the "data" queue mechanisms, both Londiste and Slony are based on,
under one new, built in mechanism with the intention to cut down the
overhead associated with them.

There is certainly a big need to coordinate this project with any
attempts made in the direction of DDL triggers. I think it is obvious
that I would later on like to make use of them within Slony to replicate
schema changes. This of course requires that such schema changes get
applied on the replica's at the correct place inside the data stream.
For example, if you "ALTER TABLE ADD COLUMN", you want to replicate all
DML changes, that happened before that ALTER TABLE grabbed its exclusive
lock, before that ALTER TABLE itself. And it would be quite disastrous
to attempt to apply any INSERT that happened on the master with that new
column before the ALTER TABLE happened on the replica.

Jan

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