Re: Transactions involving multiple postgres foreign servers, take 2

On Fri, Jun 12, 2020 at 9:54 AM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
>
> On Fri, 12 Jun 2020 at 12:40, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Fri, Jun 12, 2020 at 7:59 AM Masahiko Sawada
> > <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> > >
> > > On Thu, 11 Jun 2020 at 22:21, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > >
> > > > I have another question about
> > > > this field, why can't it be one of the status ('preparing',
> > > > 'prepared', 'committing', 'aborting', 'in-doubt') rather than having a
> > > > separate field?
> > >
> > > Because I'm using in-doubt field also for checking if the foreign
> > > transaction entry can also be resolved manually, i.g.
> > > pg_resolve_foreign_xact(). For instance, a foreign transaction which
> > > status = 'prepared' and in-doubt = 'true' can be resolved either
> > > foreign transaction resolver or pg_resolve_foreign_xact(). When a user
> > > execute pg_resolve_foreign_xact() against the foreign transaction, it
> > > sets status = 'committing' (or 'rollbacking') by checking transaction
> > > status in clog. The user might cancel pg_resolve_foreign_xact() during
> > > resolution. In this case, the foreign transaction is still status =
> > > 'committing' and in-doubt = 'true'. Then if a foreign transaction
> > > resolver process processes the foreign transaction, it can commit it
> > > without clog looking.
> > >
> >
> > I think this is a corner case and it is better to simplify the state
> > recording of foreign transactions then to save a CLOG lookup.
> >
>
> The main usage of in-doubt flag is to distinguish between in-doubt
> transactions and other transactions that have their waiter (I call
> on-line transactions).
>

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.

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