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From: Tom Lane <[email protected]>
To: Shaheed Haque <[email protected]>
Cc: pgsql-general list <[email protected]>
Subject: Re: Unexpected deadlock across two separate rows, using Postgres 17 and Django's select_for_update()
Date: Sat, 07 Mar 2026 06:45:29 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAHAc2jd=x-6hM=CoEYOaJ6ST5p-nGkTxDmh=PrwxacnkUp=31A@mail.gmail.com>
References: <CAHAc2jd=x-6hM=CoEYOaJ6ST5p-nGkTxDmh=PrwxacnkUp=31A@mail.gmail.com>

Shaheed Haque <[email protected]> writes:
> How can there be a deadlock between updates to different rows (as per the
> bolded WHERE clauses)?

In isolation, there couldn't be ... but you've told us nothing of
what these transactions did beforehand.  The simplest explanation
is that each one is already holding a lock on the row the other
one wants.

Maybe you are not committing between row updates?

If you have no better debugging ideas, try setting log_statements = all
and then examining everything the transactions did up to the failure.

			regards, tom lane

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