Content-Type: text/plain;
	charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.700.81\))
Subject: Re: Optimize LISTEN/NOTIFY
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: <38de1036-d8cf-420c-b845-edb5a946b191@app.fastmail.com>
Date: Tue, 28 Oct 2025 14:46:50 +0800
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <87E40BF8-8877-4DBD-9040-99AF8A4E6358@gmail.com>
References: <6899c044-4a82-49be-8117-e6f669765f7e@app.fastmail.com>
 <165530.1752362320@sss.pgh.pa.us>
 <02a7cd37-e2fc-4212-8b19-f8c239c95fb8@app.fastmail.com>
 <e396ecf3-4227-4918-b9ff-e9568dcebcf0@app.fastmail.com>
 <b6a427fe-2ed6-4568-85d9-207a68172617@app.fastmail.com>
 <CAK80=jhmE40KVqQ3ho37MArS7cAED1p9m7uikDxcnDmqdW7t8A@mail.gmail.com>
 <96f00bf1-cc9d-4520-9d02-9e14e7767c88@app.fastmail.com>
 <30c2aa7d-dd6c-4b68-a2e4-f217a1a34acf@app.fastmail.com>
 <CA+hUKGLrMGkWDB0cwTa0RqD+AF7O-Ywgck8aVYKwOQnZgYRRug@mail.gmail.com>
 <0b4d402a-9ac2-4aa8-acf8-8231dbe579ea@app.fastmail.com>
 <c8e84bb2-d2e5-4a77-b547-3a93c5778e7e@app.fastmail.com>
 <3095599.1758644879@sss.pgh.pa.us>
 <0dc6a2cc-5216-4dc1-9dd2-430cafc6095b@app.fastmail.com>
 <E7D8A5CD-C445-4713-B6B7-6CC1D3A71161@gmail.com>
 <baf71275-9083-41be-ae13-f80821541a1a@app.fastmail.com>
 <52CC167F-763B-4ECA-B0B4-DAB381816828@gmail.com>
 <d35a114d-204a-4b40-9284-06749532b724@app.fastmail.com>
 <9186C6D0-F7A9-482A-9183-89E530B57E36@gmail.com>
 <da0996!!!!!!d8-ecf9-490d-bbd0-2a5bdb5b115a@app.fastmail.com>
 <D1CF7CA5-213A-4FC1-86DB-052D58904A0A@gmail.com>
 <cad78ff4-aae9-4c1c-8e16-ff0ccd4957f1@app.fastmail.com>
 <1073593.1759423179@sss.pgh.pa.us>
 <4bd5e6c4-6fa7-44bb-869d-59a32a331fa8@app.fastmail.com>
 <CAFY6G8dap-bCnAnMG-2Gzew8yv2Vbi9gsx9+yszKMmd57ygfvA@mail.gmail.com>
 <85828f29-e72e-4400-94f3-9a69bc8dc239@app.fastmail.com>
 <2495353.1759860890@sss.pgh.pa.us>
 <8aeae418-92a6-4bbd-9c06-9574c79e59f7@app.fastmail.com>
 <2531672.1759868124@sss.pgh.pa.us>
 <474efa78-337c-41cd-a73a-f845a0115109@app.fastmail.com>
 <2749343.1759949176@sss.pgh.pa.us>
 <8bfca2be-1ec0-4e15-aafb-0b7b661fe936@app.fastmail.com>
 <9eba307f-f2fb-48f0-9507-2e197f39ef9e@app.fastmail.com>
 <cde2a91d-d47a-43b5-ab27-f98aa739d38e@app.fastmail.com>
 <8c71183a-0d28-4bcf-a806-78446ff95404@app.fastmail.com>
 <1009807.1760476747@sss.pgh.pa.us>
 <1F7227F5-C33D-4E2C-8511-33F1468590D0@gmail.com>
 <0a5a20d3-4621-46b3-b2ab-903f63a20dea@app.fastmail.com>
 <6F913129-ABEF-4004-AAF3-F22FC34!29AE8@gmail.com>
 <cbabbb45-ec27-47f1-a8f3-eb29073e9aef@app.fastmail.com>
 <ceab2c54-3463-4029-a7d8-895a617bb457@app.fastmail.com>
 <1547585.1760645808@sss.pgh.pa.us>
 <b8df8040-1b15-4a1a-b5f6-74acebbd2d0c@app.fastmail.com>
 <CAE7r3MLivh1sHWF06hrVXkiQbw-KChPcQsh+9CheXprm5vRVMQ@mail.gmail.com>
 <14865EB6-0BF4-462B-9072-10BDAC10C052@gmail.com>
 <CAE7r3MK-3AOdh1mpZ8hw9h6F_i0D5RMoAy7CttnfCJRpB8GJDA@mail.gmail.com>
 <0BCA1C2D-B92C-459E-B1A6-6D06BA4C62CF@gmail.com>
 <55d24cbb-e9ef-491f-a99b-b3dbd7cecdf9@app.fastmail.com>
 <38574cad-e90d-47b7-a015-753bb6bbc360@app.fastmail.com>
 <66631FB7-5BEA-4ED5-A694-9AD8B9CCFEE8@gmail.com>
 <4b7b49a5-5e1a-44a8-93e0-60457d15cb1d@app.fastmail.com>
 <82DEA2B6-6FC5-4A79-BDE3-1FD72F104A6E@gmail.com>
 <38de1036-d8cf-420c-b845-edb5a946b191@app.fastmail.com>
To: Joel Jacobson <joel@compiler.org>
Archived-At: 
 <https://www.postgresql.org/message-id/87E40BF8-8877-4DBD-9040-99AF8A4E6358%40gmail.com>
Precedence: bulk


> On Oct 28, 2025, at 14:41, Joel Jacobson <joel@compiler.org> wrote:
>=20
> On Tue, Oct 28, 2025, at 02:02, Chao Li wrote:
>>>> =46rom this perspective, we need to add a new field=20
>>>> adviancingTillPos to QueueBackendStatus. (This field was also =
missing=20
>>>> from my proposed patch).
>>>=20
>>> I'm doubtful yet another field is worth the added complexity cost.
>>>=20
>>> Before increasing the complexity further, I think we should first
>>> try to simulate somewhat realistic workloads, to see if we actually
>>> have a problem first.
>>>=20
>>> /Joel
>>>=20
>>=20
>> I don=E2=80=99t think that=E2=80=99s extra complexity, IMO, that just =
ensure =E2=80=9Cdirect=20
>> advancement=E2=80=9D to be fully functional.
>=20
> An extra field is by definition extra complexity;
> If it's worth it depends on how much we would gain from it,
> that's why I'm doubtful it's worth it.
>=20
> The extra adviancingTillPos field would only avoid wakeups in some
> scenarios, if you study the example given by Arseniy, it's easy to see
> why we would really need something like a the list of skip ranges
> Arseniy suggested, per backend, for it to be complete,
> but that's even more complexity.
>=20
> I don't think it's too bad for a backend to read through the entire
> queue, even if it contains some entires that are not interesting, when =
a
> backend is awaken, processing is fast, that's not the big cost here,
> what really costs is the context switches. But I've been wrong before,
> so could be wrong again of course. This is just based on my intuition.
>=20
>> But anyway, we should run some load tests to verify every solution to=20=

>> see how much they really improve. Do you already have or plan to work=20=

>> on a load test script?
>=20
> Yes, I'm currently working on a combined benchmark / correctness test =
suite.
>=20

Cool. Then we can run the benchmark and decide.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/