Re: [Postgres-xc-general] postgres-xc on top of existing postgres

On Mon, Jan 28, 2013 at 7:23 PM, Koichi Suzuki <koi...@gm...>wrote:

> I have not looked into it very in detail.   So this is just a guess.
>
> XC's datanode cluster contains three more system catalogues,
> pgxc_class, pgxc_node and pgxc_nodegroup and also contains many more
> build-in functions which have to be hard-coded.
>


Only adding new objects is fine. I think it does not prevent this kind of
migration.

I can think of creating new objects in pg_catalog just before switching to
Postgres-XC.

Does postgres-xc modify any existing postgres catalog tables? (adding
columns, changing types, any structure changes)?

Does postgres-xc modify any existing postgres catalog functions? (function
signatures and/or internal logic)

Do you think it's possible to map/translate existing pg_class to
pgxc_class, existing TXIDs to GXIDs, etc?

I understand that pointing "empty" GTMs and Coordinators to this new
special datanode would simply not work?
We'd have to initialize them in a special way?



>
> Even though other part of the database cluster has no serious
> difference, the above could be very serious.
>

answers to above questions would help me understand _why_ it is serious.



> It looks a good idea to allow XC to start with only one node
> configuration, and then add nodes as needed.
>
>
Yes, that's my idea also - I see there are ALTER TABLE commands which allow
to replicate/redistribute.



> Other than that, you can use pg_dump and pg_restore to move all your
> data from PostgreSQL to Postgres-XC.
>
>
I know it's a standard procedure - but in my case this would take tens of
hours, and I'm looking for other ways.


Thank you,
Filip