Re: PoC Refactor AM analyse API

From: Denis Smirnov <sd(at)arenadata(dot)io>
To: Zhihong Yu <zyu(at)yugabyte(dot)com>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: PoC Refactor AM analyse API
Date: 2021-02-19 07:59:25
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Hello, Zhihong.

Thanks for your comments.

1. I am afraid that an equivalence of "floor(val + 0.5)" to "cell(val)" is incorrect: "floor(2.1 + 0.5)" returns 2 while "cell(2.1)" returns 3. We can’t use such replacement, as you have suggested.

2. >> For compare_rows(), it seems the computation of oa and ob can be delayed to when ba == bb (after the first two if statements).
I have checked some examples of ASM code generated by different compilers with -O2/O3 flags on and didn’t see any big benefit in result CPU instructions. You can check yourself an attached example below.

Attachment Content-Type Size
simplified_compare_rows.c application/octet-stream 611 bytes

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