Re: Implement waiting for wal lsn replay: reloaded

From: Xuneng Zhou <xunengzhou(at)gmail(dot)com>
To: Álvaro Herrera <alvherre(at)kurilemu(dot)de>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>
Cc: jian he <jian(dot)universality(at)gmail(dot)com>, Tomas Vondra <tomas(at)vondra(dot)me>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Implement waiting for wal lsn replay: reloaded
Date: 2025-10-15 00:23:09
Message-ID: CABPTF7X8P42TKwoLt2WsjXxqtCh6S_goK_6st8Wov=g+yA6n4A@mail.gmail.com
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Hi,

On Tue, Oct 14, 2025 at 9:03 PM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
>
> Hi,
>
> On Sat, Oct 4, 2025 at 9:35 AM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
> >
> > Hi,
> >
> > On Sun, Sep 28, 2025 at 5:02 PM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
> > >
> > > Hi,
> > >
> > > On Fri, Sep 26, 2025 at 7:22 PM Xuneng Zhou <xunengzhou(at)gmail(dot)com> wrote:
> > > >
> > > > Hi Álvaro,
> > > >
> > > > Thanks for your review.
> > > >
> > > > On Tue, Sep 16, 2025 at 4:24 AM Álvaro Herrera <alvherre(at)kurilemu(dot)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.
> >
>
> Hi, I’ve split the patch into multiple patch sets for easier review,
> per Michael’s advice [1].
>
> [1] https://www.postgresql.org/message-id/aOMsv9TszlB1n-W7%40paquier.xyz
>

Patch 2 in v13 is corrupted and patch 3 has an error. Sorry for the
noise. Here's v14.

Best,
Xuneng

Attachment Content-Type Size
v14-0003-Implement-WAIT-FOR-command.patch application/octet-stream 47.0 KB
v14-0001-Add-pairingheap_initialize-for-shared-memory-usag.patch application/octet-stream 3.0 KB
v14-0002-Add-infrastructure-for-efficient-LSN-waiting.patch application/octet-stream 24.7 KB

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