Re: Simple IN vs IN values performace

Alexander Voytsekhovskyy <young.inbox@xxxxxxxxx> · Tue, 23 Feb 2021 11:35:42 +0200

Thanks for suggestion
with tmp tables there are another issue - there are already 5-6 tables and 2-3 IN filters. If i will replace them with tmp tables it may hit query planner limits and it will become to produce terrible query plans, for example when genetic query optimizer starts

On Tue, Feb 23, 2021 at 1:45 AM Ron <ronljohnsonjr@xxxxxxxxx> wrote:

    On 2/22/21 9:00 AM, Oleksandr Voytsekhovskyy wrote:

      Greetings,

      We have queries with IN filters with long list of
        INT values

      Sometimes, they running extremely slow, and I have
        found suggestion to use syntax

        Field IN (VALUES(1465), (1478), ...
        Instead of 

        Field IN (1465, 1478, ...
        On some cases it helps, but on other it makes
          query running 1000+ times slower

    Insert the values into a TEMPORARY TABLE, then join that to your
    main table?

      So the issue is:
      - some queries much faster with simple IN
      - some queries much faster with IN + VALUES

      Here is explain on case when it’s extremely slow:

        ->  HashAggregate  (cost=5.78..9.62 rows=385 width=4)
       Group Key: ""*VALUES*"".column1" 
                   ->  Values Scan on ""*VALUES*""  (cost=0.00..4.81 rows=385 width=4)" 
        What is the right way to pass long INT values list
          to IN filter?

      I am using PostgreSQL 13.1 on Ubuntu

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