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help / color / mirror / Atom feedFrom: Andrei Lepikhov <[email protected]>
To: Ba Jinsheng <[email protected]>
To: [email protected] <[email protected]>
Subject: Re: Performance of Query 60 on TPC-DS Benchmark
Date: Fri, 22 Nov 2024 21:32:57 +0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <SEZPR06MB649422CDEBEBBA3915154EE58A232@SEZPR06MB6494.apcprd06.prod.outlook.com>
References: <SEZPR06MB649422CDEBEBBA3915154EE58A232@SEZPR06MB6494.apcprd06.prod.outlook.com>
On 22/11/2024 18:12, Ba Jinsheng wrote:
> I think the key difference is that the patch disables the usage of Hash
> Join, which incurs a worse performance.
I see here a problem with a number of groups: when predicting it
incorrectly, Postgres doesn't use the Memoize node. Disabling HashJoin
puts NestLoop+Memoize at the place of the best path, which is chosen later.
Unfortunately, we can't see a prediction on the number of groups in
Memoize and can only guess the issue.
--
regards, Andrei Lepikhov
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