Re: Skipping logical replication transactions on subscriber side

On Tue, Jan 18, 2022 at 8:02 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Mon, Jan 17, 2022 at 10:15 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Mon, Jan 17, 2022 at 6:22 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > >
> > > >
> > > > (5)
> > > >
> > > > I can miss something here but, in one of
> > > > the past discussions, there seems a consensus that
> > > > if the user specifies XID of a subtransaction,
> > > > it would be better to skip only the subtransaction.
> > > >
> > > > This time, is it out of the range of the patch ?
> > > > If so, I suggest you include some description about it
> > > > either in the commit message or around codes related to it.
> > >
> > > How can the user know subtransaction XID? I suppose you refer to
> > > streaming protocol cases but while applying spooled changes we don't
> > > report subtransaction XID neither in server log nor
> > > pg_stat_subscription_workers.
> > >
> >
> > I also think in the current system users won't be aware of
> > subtransaction's XID but I feel Osumi-San's point is valid that we
> > should at least add it in docs that we allow to skip only top-level
> > xacts. Also, in the future, it won't be impossible to imagine that we
> > can have subtransaction's XID info also available to users as we have
> > that in the case of streaming xacts (See subxact_data).
>
> Fair point and more accurate, but I'm a bit concerned that using these
> words could confuse the user. There are some places in the doc where
> we use the words “top-level transaction” and "sub transactions” but
> these are not commonly used in the doc. The user normally would not be
> aware that sub transactions are used to implement SAVEPOINTs. Also,
> the publisher's subtransaction ID doesn’t appear anywhere on the
> subscriber. So if we want to mention it, I think we should use other
> words instead of them but I don’t have a good idea for that. Do you
> have any ideas?
>

How about changing existing text:
+ Specifies the ID of the transaction whose changes are to be skipped
+ by the logical replication worker. Setting <literal>NONE</literal>
+ resets the transaction ID.

to

Specifies the top-level transaction identifier whose changes are to be
skipped by the logical replication worker. We don't support skipping
individual subtransactions. Setting <literal>NONE</literal> resets
the transaction ID.

--
With Regards,
Amit Kapila.