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From: Tomas Vondra <[email protected]>
To: David Rowley <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: Zhihong Yu <[email protected]>
Cc: Andrey V. Lepikhov <[email protected]>
Cc: Teodor Sigaev <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: PostgreSQL Developers <[email protected]>
Subject: Re: POC: GROUP BY optimization
Date: Thu, 18 Aug 2022 09:29:43 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAApHDvr+95wJcABsqSXWcBa+yyUmJ2bq_mnZs9dUnaOi3XRVMg@mail.gmail.com>
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On 8/18/22 03:32, David Rowley wrote:
> On Thu, 18 Aug 2022 at 02:46, Tomas Vondra
> <[email protected]> wrote:
>> So I don't think the current costing is wrong, but it certainly is more
>> complex. But the test does not test what it intended - I have two ideas
>> how to make it work:
>>
>> 1) increase the number of rows in the table
>>
>> 2) increase cpu_operator_cost (for that one test?)
>>
>> 3) tweak the costing somehow, to increase the cost a bit
> 
> Why not, 4) SET parallel_setup_cost = 0;  there are plenty of other
> places we do just that so we get a parallel plan without having to
> generate enough cost to drown out the parallel worker startup cost.
> 
> Here are a couple of patches to demo the idea.
> 

Yeah, that's an option too. I should have mentioned it along with the
cpu_operator_cost.

BTW would you mind taking a look at the costing? I think it's fine, but
it would be good if someone not involved in the patch takes a look.


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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