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From: Attila Soki <[email protected]>
To: Laurenz Albe <[email protected]>
Cc: [email protected]
Subject: Re: unstable query plan on pg 16,17,18
Date: Mon, 23 Feb 2026 22:19:33 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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> On 23 Feb 2026, at 21:54, Laurenz Albe <[email protected]> wrote:
>>> The difference in the plans is under the "Subquery Scan on odg", starting with
>>> plan node 50 (everything under the "Sort").  I suspect that the mis-estimate
>>> that is at the root of the problem is here:
>>> 
>>> ->  Index Scan using table_k_late_spec_dp_end_dat_key on schema1.table_k kal  (... rows=196053 ...) (... rows=471.00 ...)
>>>      Index Cond: (kal.dp_end_dat < ('now'::cstring)::date)
>>>      Index Searches: 1
>>>      Buffers: shared hit=230 read=49
>>>      I/O Timings: shared read=0.142
>>> 
>>> PostgreSQL overestimates the row count by a factor of over 400.
>>> Try to fix that estimate and see if that gets PostgreSQL to do the right thing.
>>> 
>>> Perhaps a simple ANALYZE on the table can do the trick.
>> 
>> 
>> In the examples I used table_k to flip the plan with
>> vacuum -Upostgres -vZ -t schema1.tbl_used_in_query db1
>> in the explain output schema1.tbl_used_in_query is table_k
> 
> I cannot understand that.


sorry for being unclear.
To "switch" between the ok and wrong plans I execute
vacuumdb -Upostgres -vZ -t schema1.table_k db1
multiple times (1x-3x) until the plan flips. So I thought the table should already have been analyzed.
In my first email I called table_k as the "tbl_used_in_query"
or have I misunderstood that with the analyze?

Thanks

Regards,
Attila

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