From: Tom Lane <tgl@sss.pgh.pa.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
cc: James Pang <jamespang886@gmail.com>,
        pgsql-performance@lists.postgresql.org
Subject: Re: a lot of session wait on lock relation
In-reply-to: <54994813530a36c0280fd8779e65ad1ad73d910a.camel@cybertec.at>
References: 
 <CAHgTRfdEVMi_YVuq3M4R4uARhXQ8ZgkMid3LhxjFbS+Y+Z_8GQ@mail.gmail.com>
 <54994813530a36c0280fd8779e65ad1ad73d910a.camel@cybertec.at>
Comments: In-reply-to Laurenz Albe <laurenz.albe@cybertec.at>
	message dated "Thu, 15 May 2025 14:08:05 +0200"
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Date: Thu, 15 May 2025 09:24:30 -0400
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Laurenz Albe <laurenz.albe@cybertec.at> writes:
> On Thu, 2025-05-15 at 16:27 +0800, James Pang wrote:
>> why inserts into partition table cause "relation lock" ?

> Something else does; use the pg_blocking_pids() function with the proces=
s ID of
> a blocked backend to find out who is holding the lock.

More specifically: the inserts are only trying to get a shared lock.
If they are blocked, it's because some other operation is already
holding an exclusive lock on the table and is not letting go.
Look for uncommitted DDL changes.

More details about that at [1].

			regards, tom lane

[1] https://www.postgresql.org/docs/current/explicit-locking.html#LOCKING-=
TABLES