Re: Implement waiting for wal lsn replay: reloaded

Hi, Xuneng!

On Sun, Sep 14, 2025 at 4:51 PM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
>
> On Sun, Sep 14, 2025 at 3:31 AM Alexander Korotkov <aekorotkov(at)gmail(dot)com> wrote:
> > On Wed, Aug 27, 2025 at 6:54 PM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
> > > I did a rebase for the patch to v8 and incorporated a few changes:
> > >
> > > 1) Updated documentation, added new tests, and applied minor code
> > > adjustments based on prior review comments.
> > > 2) Tweaked the initialization of waitReplayLSNState so that
> > > non-backend processes can call wait for replay.
> > >
> > > Started a new thread [1] and attached a patch addressing the polling
> > > issue in the function
> > > read_local_xlog_page_guts built on the infra of patch v8.
> > >
> > > [1] https://www.postgresql.org/message-id/CABPTF7Vr99gZ5GM_ZYbYnd9MMnoVW3pukBEviVoHKRvJW-dE3g@mail.gmail.com
> > >
> > > Feedbacks welcome.
> >
> > Thank you for your reviewing and revising this patch.
> >
> > I see you've integrated most of your points expressed in [1]. I went
> > though them and I've integrated the rest of them. Except this one.
> >
> > > 11) The synopsis might read more clearly as:
> > > - WAIT FOR LSN '<lsn>' [ TIMEOUT <milliseconds | 'duration-with-units'> ] [ NO_THROW ]
> >
> > I didn't find examples on how we do the similar things on other places
> > of docs. This is why I decided to leave this place as it currently
> > is.
>
> +1. I re-check other commands with similar parameter patterns, and
> they follow the approach in v9.
>
> >
> > Also, I found some mess up with typedefs.list. I've returned the
> > changes to typdefs.list back and re-indented the sources.
>
> Thanks for catching and fixing that.
>
> > I'd like to ask your opinion of the way this feature is implemented in
> > terms of grammar: generic parsing implemented in gram.y and the rest
> > is done in wait.c. I think this approach should minimize additional
> > keywords and states for parsing code. This comes at the price of more
> > complex code in wait.c, but I think this is a fair price.
>
> It's LGTM. The same pattern is observed in VACUUM, EXPLAIN, and CREATE
> PUBLICATION - all use minimal grammar rules that produce generic
> option lists, with the actual interpretation done in their respective
> implementation files. The moderate complexity in wait.c seems
> acceptable.

The attached revision of patch contains fix of the typo in the comment
you reported off-list.

------
Regards,
Alexander Korotkov
Supabase