Re: Transactions involving multiple postgres foreign servers, take 2

On Mon, Dec 28, 2020 at 11:24 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Wed, Nov 25, 2020 at 9:50 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > Since the previous version conflicts with the current HEAD I've
> > attached the rebased version patch set.
>
> Rebased the patch set again to the current HEAD.
>
> The discussion of this patch is very long so here is a short summary
> of the current state:
>
> It’s still under discussion which approaches are the best for the
> distributed transaction commit as a building block of built-in sharing
> using foreign data wrappers.
>
> Since we’re considering that we use this feature for built-in
> sharding, the design depends on the architecture of built-in sharding.
> For example, with the current patch, the PostgreSQL node that received
> a COMMIT from the client works as a coordinator and it commits the
> transactions using 2PC on all foreign servers involved with the
> transaction. This approach would be good with the de-centralized
> sharding architecture but not with centralized architecture like the
> GTM node of Postgres-XC and Postgres-XL that is a dedicated component
> that is responsible for transaction management. Since we don't get a
> consensus on the built-in sharding architecture yet, it's still an
> open question that this patch's approach is really good as a building
> block of the built-in sharding.
>
> On the other hand, this feature is not necessarily dedicated to the
> built-in sharding. For example, the distributed transaction commit
> through FDW is important also when atomically moving data between two
> servers via FDWs. Using a dedicated process or server like GTM could
> be an over solution. Having the node that received a COMMIT work as a
> coordinator would be better and straight forward.
>
> There is no noticeable TODO in the functionality so far covered by
> this patch set. This patchset adds new FDW APIs to support 2PC,
> introduces the global transaction manager, and implement those FDW
> APIs to postgres_fdw. Also, it has regression tests and documentation.
> Transactions on foreign servers involved with the distributed
> transaction are committed using 2PC. Committing using 2PC is performed
> asynchronously and transparently to the user. Therefore, it doesn’t
> guarantee that transactions on the foreign server are also committed
> when the client gets an acknowledgment of COMMIT. The patch doesn't
> cover synchronous foreign transaction commit via 2PC is not covered by
> this patch as we still need a discussion on the design.
>

I've attached the rebased patches to make cfbot happy.

Regards,

--
Masahiko Sawada
EnterpriseDB: https://www.enterprisedb.com/