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From: Israel Brewster <[email protected]>
To: Adrian Klaver <[email protected]>
Cc: PostgreSQL General <[email protected]>
Subject: Re: PostgreSQL 15-->18 slowdown?
Date: Fri, 26 Jun 2026 10:19:06 -0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

On Jun 26, 2026, at 10:14 AM, Adrian Klaver <[email protected]> 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?
>> 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.

Right, sorry. It’s the same query as in the first one though. Only difference is sequence scan off.

---
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


> 
> 
>> ---
>> 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
> 

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