Re: [Postgres-xc-general] Questions about Postgres-XC

[Mason S. <ms...@tr...>]

On Thu, May 29, 2014 at 7:27 AM, Alan Bryant <ala...@hd...> wrote:

>
>
>  - Can we shard on schema? (i.e. put some schemas in one location and
> other schemas in different locations, sharded the same way rows are?) Or if
> not, can we shard one table, and have functions execute on the same node as
> some controlling row?
>
>
>  No.
>
>    Interesting. This leaves us with the "one big table" approach, just
> spread across the data nodes. Aren't there performance issues with having
> massive individual tables? What techniques exist to help with this?
>

The individual tables can be replicated or sharded, such as a hash based on
one of the columns in the table.

A parent-child type of relation can be sharded on a primary key of the
parent, and the foreign key referencing that table in the child. The
planner recognizes that this data will co-exist on the same node and
"push-down" joins.

Other tables can be replicated, with an exact copy on each node if desired.
Here joins can always be pushed down. If a query only involves replicated
tables, it will just be sent to one single node. If a coordinator and data
node are on the same server, one can configure the system to prefer to get
this data from a local data node.


>
> Partitioning is one option I guess, using a different (but compatible)
> scheme than the sharding key, perhaps a different bitmask on the same key.
>

At the moment users cannot specify an arbitrary expression like a bitmask.
A modulo option exists, however. I think this is an item that should be a
relatively high-ish priority on the to do list.


>
> Another question is upgrade. We use schemas primarily to make logical
> upgrades possible while online, but what about Postgres-XC itself... what
> is the upgrade model for Postgres-XC? (say, between major PostgreSQL
> versions)
>
>
This is another area that can be improved, leveraging pg_upgrade. For now,
dump and restore...



> Thanks!
> -Alan
>

Regards,

-- 
Mason Sharp

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