Re: Transactions involving multiple postgres foreign servers, take 2

On Wed, 3 Jun 2020 at 14:50, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Tue, May 19, 2020 at 12:33 PM Masahiko Sawada
> <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> >
> > I think that the current three values are useful for users. The
> > ‘required’ mode is used when users want to ensure all writes involved
> > with the transaction are committed atomically. That being said, as
> > some FDW plugin might not support the prepare API we cannot force
> > users to use this mode all the time when using atomic commit.
> > Therefore ‘prefer’ mode would be useful for this case. Both modes use
> > 2pc only when it's required for atomic commit.
> >
> > So what do you think my idea that adding the behavior you proposed as
> > another new mode? As it’s better to keep the first version simple as
> > much as possible
> >
>
> If the intention is to keep the first version simple, then why do we
> want to support any mode other than 'required'? I think it will limit
> its usage for the cases where 2PC can be used only when all FDWs
> involved support Prepare API but if that helps to keep the design and
> patch simpler then why not just do that for the first version and then
> extend it later. OTOH, if you think it will be really useful to keep
> other modes, then also we could try to keep those in separate patches
> to facilitate the review and discussion of the core feature.

‘disabled’ is the fundamental mode. We also need 'disabled' mode,
otherwise existing FDW won't work. I was concerned that many FDW
plugins don't implement FDW transaction APIs yet when users start
using this feature. But it seems to be a good idea to move 'prefer'
mode to a separate patch while leaving 'required'. I'll do that in the
next version patch.

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
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