public inbox for [email protected]  

help / color / mirror / Atom feed

From: Laurenz Albe <[email protected]>
To: [email protected]
To: [email protected]
Subject: Re: Unexpected deadlock across two separate rows, using Postgres 17 and Django's select_for_update()
Date: Sun, 08 Mar 2026 19:03:04 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CAHAc2jd=x-6hM=CoEYOaJ6ST5p-nGkTxDmh=PrwxacnkUp=31A@mail.gmail.com>
	<[email protected]>

On Sun, 2026-03-08 at 15:15 +0000, [email protected] wrote:
> This is pure speculation.
> It's possible that using SELECT FOR UPDATE also locks the rows in the parent tables referenced in the field list.
> I believe this happened in older versions of PostgreSQL.

I thought about that too, but since both updates affect the same table,
the foreign key would have to reference the table itself.

You are right that a SELECT ... FOR UPDATE will place a lock on any
referenced row (and FOR UPDATE will probably use a lock that is too
strong!), but those locks would still be SHARE locks, which can
coexist.

Yours,
Laurenz Albe

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: Unexpected deadlock across two separate rows, using Postgres 17 and Django's select_for_update()
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox