Horton

Re: Implement waiting for wal lsn replay: reloaded

Xuneng Zhou <xunengzhou@gmail.com>

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From: Xuneng Zhou <xunengzhou@gmail.com>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@lists.postgresql.org>, Andres Freund <andres@anarazel.de>, Álvaro Herrera <alvherre@kurilemu.de>, Michael Paquier <michael@paquier.xyz>, jian he <jian.universality@gmail.com>, Tomas Vondra <tomas@vondra.me>, Yura Sokolov <y.sokolov@postgrespro.ru>
Date: 2025-12-18T12:24:38Z
Lists: pgsql-hackers 
Hi Alexander,

On Thu, Dec 18, 2025 at 6:38 PM Alexander Korotkov <aekorotkov@gmail.com> wrote:
>
> Hi, Xuneng!
>
> On Tue, Dec 16, 2025 at 6:46 AM Xuneng Zhou <xunengzhou@gmail.com> wrote:
> > Remove the erroneous WAIT_LSN_TYPE_COUNT case from the switch
> > statement in v5 patch 1.
>
> Thank you for your work on this patchset.  Generally, it looks like
> good and quite straightforward extension of the current functionality.
> But this patch adds 4 new unreserved keywords to our grammar.  Do you
> think we can put mode into with options clause?
>

Thanks for pointing this out. Yeah, 4 unreserved keywords add
complexity to the parser and it may not be worthwhile since replay is
expected to be the common use scenario. Maybe we can do something like
this:

-- Default (REPLAY mode)
WAIT FOR LSN '0/306EE20' WITH (TIMEOUT '1s');

-- Explicit REPLAY mode
WAIT FOR LSN '0/306EE20' WITH (MODE 'replay', TIMEOUT '1s');

-- WRITE mode
WAIT FOR LSN '0/306EE20' WITH (MODE 'write', TIMEOUT '1s');

If no mode is set explicitly in the options clause, it defaults to
replay. I'll update the patch per your suggestion.

-- 
Best,
Xuneng