Message-ID: <b7da2330-1054-4bb8-939a-cb05d377f70f@gmail.com>
Date: Mon, 12 May 2025 14:08:21 +0200
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Subject: Re: inefficient/wrong plan cache mode selection for queries with
 partitioned tables (postgresql 17)
To: Maxim Boguk <maxim.boguk@gmail.com>,
 pgsql-performance@lists.postgresql.org
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From: Andrei Lepikhov <lepihov@gmail.com>
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On 5/12/25 13:49, Maxim Boguk wrote:
> I suspect this situation should be quite common with queries over 
> partitioned tables (where planning time is usually quite a high).
> 
> Any suggestions what could be done there outside of using 
> force_generic_plan for a particular db user (which will kill performance 
> in other queries for sure)?
Thanks for this puzzle!
I suppose, in case generic planning is much faster than custom one, 
there are two candidates exist:
1. Touching the index during planning causes too much overhead - see 
get_actual_variable_range
2. You have a massive default_statistics_target for a table involved.

So, to clarify the problem, may you provide EXPLAIN (without analyze) 
with BUFFERS ON ?
Also, could you provide extra information on the statistics involved? 
For each column (I think created_at is the most important one), show the 
size of MCV and histogram arrays.

-- 
regards, Andrei Lepikhov