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Message-ID: <064ae3fd-b34e-4c72-94dc-5c5173d999a0@aklaver.com>
Date: Fri, 26 Jun 2026 11:16:23 -0700
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Subject: Re: PostgreSQL 15-->18 slowdown?
From: Adrian Klaver <adrian.klaver@aklaver.com>
To: Israel Brewster <ijbrewster@alaska.edu>,
 PostgreSQL General <pgsql-general@lists.postgresql.org>
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On 6/26/26 11:14 AM, Adrian Klaver wrote:
> 
> 
> 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?

Yes you did: "I get a command timeout after at least half an hour"

Was not thinking.
>>
>> 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
>>
> 
> 
>