Re: Implement waiting for wal lsn replay: reloaded - Mailing list pgsql-hackers

Hi,

On Tue, Dec 16, 2025 at 1:49 PM Chao Li <li.evan.chao@gmail.com> wrote:
>
>
>
> > On Oct 4, 2025, at 09:35, Xuneng Zhou <xunengzhou@gmail.com> wrote:
> >
> > Hi,
> >
> > On Sun, Sep 28, 2025 at 5:02 PM Xuneng Zhou <xunengzhou@gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> On Fri, Sep 26, 2025 at 7:22 PM Xuneng Zhou <xunengzhou@gmail.com> wrote:
> >>>
> >>> Hi Álvaro,
> >>>
> >>> Thanks for your review.
> >>>
> >>> On Tue, Sep 16, 2025 at 4:24 AM Álvaro Herrera <alvherre@kurilemu.de> wrote:
> >>>>
> >>>> On 2025-Sep-15, Alexander Korotkov wrote:
> >>>>
> >>>>>> 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.
> >>>>
> >>>> Actually I find the code in ExecWaitStmt pretty unusual.  We tend to use
> >>>> lists of DefElem (a name optionally followed by a value) instead of
> >>>> individual scattered elements that must later be matched up.  Why not
> >>>> use utility_option_list instead and then loop on the list of DefElems?
> >>>> It'd be a lot simpler.
> >>>
> >>> I took a look at commands like VACUUM and EXPLAIN and they do follow
> >>> this pattern. v11 will make use of utility_option_list.
> >>>
> >>>> Also, we've found that failing to surround the options by parens leads
> >>>> to pain down the road, so maybe add that.  Given that the LSN seems to
> >>>> be mandatory, maybe make it something like
> >>>>
> >>>> WAIT FOR LSN 'xy/zzy' [ WITH ( utility_option_list ) ]
> >>>>
> >>>> This requires that you make LSN a keyword, albeit unreserved.  Or you
> >>>> could make it
> >>>> WAIT FOR Ident [the rest]
> >>>> and then ensure in C that the identifier matches the word LSN, such as
> >>>> we do for "permissive" and "restrictive" in
> >>>> RowSecurityDefaultPermissive.
> >>>
> >>> Shall make LSN an unreserved keyword as well.
> >>
> >> Here's the updated v11.  Many thanks Jian for off-list discussions and review.
> >
> > v12 removed unused
> > +WaitStmt
> > +WaitStmtParam in pgindent/typedefs.list.
> >
> > Best,
> > Xuneng
> > <v12-0001-Implement-WAIT-FOR-command.patch>
>
> I just tried to review v12 but failed to “git am”. Can you please rebase the change?
>

Thanks for looking into this.

That series of patches implementing the WAIT FOR REPLAY command was
applied last month (8af3ae0d , 447aae13, 3b4e53a0, a1f7f91b) in its
version 20. The current v6 patch set [1] [2] primarily extends the
WAIT FOR functionality to support waiting for flush and write LSNs on
a replica by adding a MODE parameter [3]. This made me wonder whether
it would be more appropriate to start a new thread for the extension,
though it is still part of the same WAIT FOR command.

[1] https://commitfest.postgresql.org/patch/6265/
[2] https://www.postgresql.org/message-id/CABPTF7XKti620ZAOXPGuhSZxCKyaV_9stq7ruhnuxvshUxCeRQ@mail.gmail.com
[3] https://www.postgresql.org/message-id/CAPpHfdt4b0wBC4+Oopp_eFQnNjDvxwQLrQ1r4GMJfCY0XWP0dA@mail.gmail.com

--
Best,
Xuneng