Re: Transactions involving multiple postgres foreign servers, take 2

On Fri, Jun 12, 2020 at 6:24 PM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
>
> On Fri, 12 Jun 2020 at 19:24, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > > > Which are these other online transactions? I had assumed that foreign
> > > > transaction resolver process is to resolve in-doubt transactions but
> > > > it seems it is also used for some other purpose which anyway was the
> > > > next question I had while reviewing other sections of docs but let's
> > > > clarify as it came up now.
> > >
> > > When a distributed transaction is committed by COMMIT command, the
> > > postgres backend process prepare all foreign transaction and commit
> > > the local transaction.
> > >
>
> Thank you for your review comments! Let me answer your question first.
> I'll see the review comments.
>
> >
> > Does this mean that we will mark the xid as committed in CLOG of the
> > local server?
>
> Well what I meant is that when the client executes COMMIT command, the
> backend executes PREPARE TRANSACTION command on all involved foreign
> servers and then marks the xid as committed in clog in the local
> server.
>

Won't it create an inconsistency in viewing the data from the
different servers? Say, such a transaction inserts one row into a
local server and another into the foreign server. Now, if we follow
the above protocol, the user will be able to see the row from the
local server but not from the foreign server.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com