Re: Transactions involving multiple postgres foreign servers, take 2 - Mailing list pgsql-hackers

On Tue, Sep 8, 2020 at 8:05 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>
> On 2020/09/08 10:34, Amit Kapila wrote:
> > On Mon, Sep 7, 2020 at 2:29 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
> >>
> >> IMO it's not easy to commit this 2PC patch at once because it's still large
> >> and complicated. So I'm thinking it's better to separate the feature into
> >> several parts and commit them gradually.
> >>
> >
> > Hmm, I don't see that we have a consensus on the design and or
> > interfaces of this patch and without that proceeding for commit
> > doesn't seem advisable. Here are a few points which I remember offhand
> > that require more work.
>
> Thanks!
>
> > 1. There is a competing design proposed and being discussed in another
> > thread [1] for this purpose. I think both the approaches have pros and
> > cons but there doesn't seem to be any conclusion yet on which one is
> > better.
>
> I was thinking that [1] was discussing global snapshot feature for
> "atomic visibility" rather than the solution like 2PC for "atomic commit".
> But if another approach for "atomic commit" was also proposed at [1],
> that's good. I will check that.
>

Okay, that makes sense.

> > 2. In this thread, we have discussed to try integrating this patch
> > with some other FDWs (say MySQL, mongodb, etc.) to ensure that the
> > APIs we are exposing are general enough that other FDWs can use them
> > to implement 2PC. I could see some speculations about the same but no
> > concrete work on the same has been done.
>
> Yes, you're right.
>
> > 3. In another thread [1], we have seen that the patch being discussed
> > in this thread might need to re-designed if we have to use some other
> > design for global-visibility than what is proposed in that thread. I
> > think it is quite likely that can happen considering no one is able to
> > come up with the solution to major design problems spotted in that
> > patch yet.
>
> You imply that global-visibility patch should be come first before "2PC" patch?
>

I intend to say that the global-visibility work can impact this in a
major way and we have analyzed that to some extent during a discussion
on the other thread. So, I think without having a complete
design/solution that addresses both the 2PC and global-visibility, it
is not apparent what is the right way to proceed. It seems to me that
rather than working on individual (or smaller) parts one needs to come
up with a bigger picture (or overall design) and then once we have
figured that out correctly, it would be easier to decide which parts
can go first.

-- 
With Regards,
Amit Kapila.