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From: Attila Soki <[email protected]>
To: Andrei Lepikhov <[email protected]>
Cc: [email protected]
Cc: Laurenz Albe <[email protected]>
Subject: Re: unstable query plan on pg 16,17,18
Date: Tue, 24 Feb 2026 16:50:55 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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On 24 Feb 2026, at 12:37, Attila Soki <[email protected]> wrote:
> On 24 Feb 2026, at 12:09, Andrei Lepikhov <[email protected]> wro
>> This update gives us more useful details. In PG14, the join search problem involved at most 9 relations. In PG19, the maximum is now 18 joins. Do you know what your join_collapse_limit is set to? It looks like subplan pull-ups have made things more complex.
>> First, we should look into any possible 'rescan cost' issues on our side as developers.
>> On your end, please check the join_collapse_limit setting. If needed, try increasing it to around 20. This might help.
> 
> join_collapse_limit is not set, so it is the default, 8
> I will try if something around 20 helps.

I tried it with join_collapse_limit 10,15, 20 with no success,
but with join_collapse_limit 1, 5, 7 I get the good plan.

Then I set join_collapse_limit back to default and flipped the plan again with vacuumdb until i get the good plan with the default join_collapse_limit.
Then I tried to increase join_collapse_limit until the query (or planning) runs longer than 28 sec.
I tried 1, 5 ,7, 8, 9 ,10, 15, 20, 40, 100 but the query runs stable with 17-20 sec runtime. so there is still something weird with the statistics.

Now with join_collapse_limit=7 works for me and I am not able to flip the plan. makes that sense?

should I still test with increased statistic on table_k.dp_end_dat as Laurenz suggested?

I could now share some general infos about the query, if you still interested.

thanks.

regards
Attila

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