Date: Wed, 7 Jan 2026 17:06:22 -0600
From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>,
	Euler Taveira <euler@eulerto.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: improve performance of pg_dump with many sequences
Message-ID: <aV7m7rTty4KAb-tF@nathan>
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I'm still looking into this, but here are some preliminary thoughts.

On Mon, Dec 29, 2025 at 12:26:01PM -0500, Tom Lane wrote:
> In the no-good-deed-goes-unpunished department: pg_dump's use
> of pg_get_sequence_data() (nee pg_sequence_read_tuple()) is
> evidently responsible for the complaint in bug #19365 [1]
> that pg_dump can no longer survive concurrent sequence drops.

This seems to be reproducible on older versions.  With a well-timed sleep
right before dumpSequenceData()'s pre-v18 query, I can produce a
relation-does-not-exist error with a concurrent sequence drop.  Perhaps v18
made this easier to reach, but given it moved the sequence tuple access to
collectSequences()'s query, I'm not sure why that would be.

> BTW, I'm unconvinced that pg_dump behaves sanely when this function
> does return nulls.  I think the ideal thing would be for it to skip
> issuing setval(), but right now it looks like it will issue one with
> garbage values.

Before v18, pg_dump just ERRORs due to insufficient privileges on a
sequence.  IMHO that makes sense.  If you ask pg_dump to dump something you
don't have privileges on, I'd expect it to error instead of silently
skipping it.

-- 
nathan