Message-ID: <692a315e-6dd8-4194-8c7f-c45425852e77@cornfield.me.uk>
Date: Mon, 7 Apr 2025 20:25:28 +0100
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Subject: Re: Slow timestamp query after upgrading from Pg13 to Pg16
To: Laurenz Albe <laurenz.albe@cybertec.at>, pgsql-general@postgresql.org
References: <27b2975b-c078-45cf-815d-eddbedbda153@cornfield.me.uk>
 <092224fb0376bbc6a5f777199dde3cb9cd1ebf99.camel@cybertec.at>
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From: Simon Windsor <simon.windsor@cornfield.me.uk>
In-Reply-To: <092224fb0376bbc6a5f777199dde3cb9cd1ebf99.camel@cybertec.at>
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Hi

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/

Simon

On 07/04/2025 15:51, Laurenz Albe wrote:
> On Mon, 2025-04-07 at 15:48 +0100, Simon Windsor wrote:
>> After upgrading a Db from Pg13 (Centos) to Pg16(Ubuntu) some queries
>> on a simple, large table (200M rows) are very slow
> If you used "pg_upgrade", did you ANALYZE the database?
>
> If that is not the problem, we can't guess what your problem might be
> unless you provide EXPLAIN (ANALYZE, BUFFERS, SETTINGS) output for auch a
> slow query.  Ideally, add the same information for the fast v13 case.
>
> Yours,
> Laurenz Albe

-- 
Simon Windsor

Eml: simon.windsor@cornfield.me.uk
Mob: 0755 197 9733


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