Re: pgsql: Add ALTER SUBSCRIPTION ... SKIP.

On Sun, Sep 4, 2022 at 8:39 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Sun, Sep 4, 2022 at 1:48 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> >
> > On 2022-Mar-22, Amit Kapila wrote:
> >
> > > Add ALTER SUBSCRIPTION ... SKIP.
> >
> > There are two messages here that seem oddly worded.
> >
> > msgid "start skipping logical replication transaction finished at %X/%X"
> > msgid "done skipping logical replication transaction finished at %X/%X"
> >
> > Two complaints here. First, the phrases "start / finished" and "done /
> > finished" look very strange. It took me a while to realize that
> > "finished" refers to the LSN, not to the skipping operation. Do we ever
> > talk about a transaction "finished at XYZ" as opposed to a transaction
> > whose LSN is XYZ? (This became particularly strange when I realized
> > that the LSN might come from a PREPARE.)
> >
>
> The reason to add "finished at ..." was to be explicit about whether
> it is a starting LSN or an end LSN of a transaction. We do have such
> differentiation in ReorderBufferTXN (first_lsn ... end_lsn).
>
> > Second, "logical replication transaction". Is it not a regular
> > transaction that we happen to be processing via logical replication?
> >
> > I think they should say something like
> >
> > "logical replication starts skipping transaction with LSN %X/%X"
> > "logical replication completed skipping transaction with LSN %X/%X"
> >
>
> This looks better to me.

+1

> If you find the above argument to
> differentiate between the start and end LSN convincing then we can
> think of replacing "with" in the above messages with "finished at". I
> see your point related to using "finished at" for PREPARE may not be a
> good idea but I don't have better ideas for the same.

Given that the user normally doesn't need to be aware of the
difference between start LSN and end LSN in the context of using this
feature, I think we can use "with LSN %X/%X".

Regards,

--
Masahiko Sawada