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From: Laurenz Albe <[email protected]>
To: Simon Windsor <[email protected]>
To: [email protected]
Subject: Re: Slow timestamp query after upgrading from Pg13 to Pg16
Date: Tue, 08 Apr 2025 08:40:11 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>

On Mon, 2025-04-07 at 20:25 +0100, Simon Windsor wrote:
> We used pg_dump|pg_restore to migrate the data.
> 
> The full explain plan is at https://explain.depesz.com/s/742M. The SQL
> 
> explain (analyze, buffers) select count(*) from consignments where 
> (req_status_tstamp >= '2025-03-28 00:00'::timestamp and 
> req_status_tstamp <= '2025-03-28 01:00'::timestamp);
> 
> takes 2-3s with the old Pg13 DB, and over a minute with Pg16
> 
> After spending many hours looking at DB settings and Statistic settings 
> I am at a loss/

Thanks.

- Can you show the index definitions on that table?

- If you "SET enable_seqscan = off;" in an interactive session, PostgreSQL
  should choose an index scan if possible.  Can you show the
  EXPLAIN (ANALYZE, BUFFERS) output for that execution?

Yours,
Laurenz Albe

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