Message-ID: <b0752470-6536-4a00-a00a-b2111986b2fd@joeconway.com>
Date: Mon, 16 Feb 2026 10:42:40 -0500
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Subject: Re: A serious change in performance between PG 15 and PG 16, 17, 18.
To: Clive Boughton <clive.boughton@softimp.com.au>,
 pgsql-performance@postgresql.org
References: <5A68A5FD-3CD2-4863-B274-51804235BE3C@softimp.com.au>
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From: Joe Conway <mail@joeconway.com>
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On 2/15/26 22:49, Clive Boughton wrote:
> After adding quite basic indexing, that time was reduced to 1 or 2
> minutes. PG 10.2 remained in place until 2023 when the DB was
> upgraded to PG 15.2 with no problems. In fact performance increased.

> When I recently upgraded to PG 18.1 (without any changes to the DB 
> functions or tables, or indexing) it took 7-10 hours to produce the same 
> result - a *300-600 times decrease in performance*.

> My first step was to reduce the jump in versioning of PG from 15 to 18 
> down to 15 - 16.  This action produced the same very poor performance 
> result as when using PG 18.1


Are some of your indexes on collatable columns? If so, what version of 
glibc is on each of your systems (i.e. did you change OS major versions)?


-- 
Joe Conway
PostgreSQL Contributors Team
Amazon Web Services: https://aws.amazon.com