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From: Andres Freund <[email protected]>
To: Heikki Linnakangas <[email protected]>
Cc: vignesh C <[email protected]>
Cc: [email protected]
Cc: Thomas Munro <[email protected]>
Cc: Melanie Plageman <[email protected]>
Cc: Yura Sokolov <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: David Rowley <[email protected]>
Subject: Re: refactoring relation extension and BufferAlloc(), faster COPY
Date: Sat, 11 Feb 2023 14:04:13 -0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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On 2023-02-11 13:36:51 -0800, Andres Freund wrote:
> Even though it's not a correctness issue, it seems to me that
> DropRelationsAllBuffers() etc ought to check if the buffer is BM_TAG_VALID,
> before doing anything further.  Particularly in DropRelationsAllBuffers(), the
> check we do for each buffer isn't cheap. Doing it for buffers that don't even
> have a tag seems .. not smart.

There's a small regression for a single relation, but after that it's a clear
benefit.

32GB shared buffers, empty. The test creates N new relations and then rolls
back.

		tps		tps
num relations	HEAD		precheck
1		46.11		45.22
2		43.24		44.87
4		35.14		44.20
8		28.72		42.79

I don't understand the regression at 1, TBH.  I think it must be a random code
layout issue, because the same pre-check in DropRelationBuffers() (exercised
via TRUNCATE of a newly created relation), shows a tiny speedup.

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