Re: Simple IN vs IN values performace

[Pavel Stehule <pavel.stehule@xxxxxxxxx>]

Hi

út 23. 2. 2021 v 10:36 odesílatel Alexander Voytsekhovskyy <young.inbox@xxxxxxxxx> napsal:

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

you can increase these limits - they are relatively low, and can be increased on modern CPU.

https://www.postgresql.org/docs/current/runtime-config-query.html

Regards

Pavel

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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