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Message-ID: <2ce465f0-f7f3-4c6a-9f68-b53439416336@aklaver.com>
Date: Fri, 26 Jun 2026 11:14:56 -0700
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Subject: Re: PostgreSQL 15-->18 slowdown?
To: Israel Brewster <ijbrewster@alaska.edu>,
 PostgreSQL General <pgsql-general@lists.postgresql.org>
References: <4A6D9280-1409-42A8-9A1F-99E2A558E2BB@alaska.edu>
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From: Adrian Klaver <adrian.klaver@aklaver.com>
In-Reply-To: <4A6D9280-1409-42A8-9A1F-99E2A558E2BB@alaska.edu>
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On 6/26/26 10:58 AM, Israel Brewster wrote:
> In postgreSQL 15, I had the below query that worked quickly. Now, I make 
> no claims that the query is the best possible, or even a good query, but 
> it DID work, and it did so quickly enough to be un-noticable when running.
> 
> Then I upgrade to PostgreSQL 18 - and now the query never completes (as 
> in, I get a command timeout after at least half an hour before I get a 
> result). Looking at the EXPLAIN (https://explain.depesz.com/s/llAQ 
> <https://explain.depesz.com/s/llAQ>) makes it pretty obvious why: we 
> have a sequence scan on a large table inside a nested loop - and that 
> sequence scan is apparently not short circuiting.

The link provided shows no times or rows, did you pick the correct one?
> 
> I tried the obvious: REINDEX database and VACUUM ANALYZE, but neither 
> helped. I have my default_statistics_target set to 500 at the moment.
> 
> Then I tried SET enable_seqscan = off; Lo and behold, the query ran in 
> only 123.888 ms (fun number :-D ) - https://explain.depesz.com/s/K2K9 
> <https://explain.depesz.com/s/K2K9>

This one does not show the actual query.


> ---
> Israel Brewster
> Software Engineer
> Alaska Volcano Observatory
> Geophysical Institute - UAF
> 2156 Koyukuk Drive
> Fairbanks AK 99775-7320
> Work: 907-474-5172
> cell:  907-328-9145
>