Re: Logical Replication WIP

On 09/08/16 09:59, Masahiko Sawada wrote:
>>> On 2016-08-05 17:00:13 +0200, Petr Jelinek wrote:
>>>> as promised here is WIP version of logical replication patch.
>>>
>
> Thank you for working on this!

Thanks for looking!

>
> I've applied these patches to current HEAD, but got the following error.
>
> libpqwalreceiver.c:48: error: redefinition of typedef ‘WalReceiverConnHandle’
> ../../../../src/include/replication/walreceiver.h:137: note: previous
> declaration of ‘WalReceiverConnHandle’ was here
> make[2]: *** [libpqwalreceiver.o] Error 1
> make[1]: *** [install-backend/replication/libpqwalreceiver-recurse] Error 2
> make: *** [install-src-recurse] Error 2
>
> After fixed this issue with attached patch, I used logical replication a little.
> Some random comments and questions.
>

Interesting, my compiler does have problem. Will investigate.

> The logical replication launcher process and the apply process are
> implemented as a bgworker. Isn't better to have them as an auxiliary
> process like checkpointer, wal writer?
> IMO the number of logical replication connections should not be
> limited by max_worker_processes.
>

What Craig said reflects my rationale for doing this pretty well.

> We need to set the publication up by at least CREATE PUBLICATION and
> ALTER PUBLICATION command.
> Can we make CREATE PUBLICATION possible to define tables as well?
> For example,
> CREATE PUBLICATION mypub [ TABLE table_name, ...] [WITH options]

Agreed, that just didn't make it to the first cut to -hackers. We've 
been also thinking of having special ALL TABLES parameter there that 
would encompass whole db.

> --
> This patch can not drop the subscription.
>
> =# drop subscription sub;
> ERROR:  unrecognized object class: 6102
>

Yeah that's because of the patch 0006, I didn't finish all the 
dependency tracking for the pg_subscription_rel catalog that it adds 
(which is why I called it PoC). I expect to have this working in next 
version (there is still quite a bit of polish work needed in general).

--   Petr Jelinek                  http://www.2ndQuadrant.com/  PostgreSQL Development, 24x7 Support, Training &
Services