Re: Yet another fast GiST build

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Cc: Peter Geoghegan <pg(at)bowt(dot)ie>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Darafei Komяpa Praliaskouski <me(at)komzpa(dot)net>, Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com>
Subject: Re: Yet another fast GiST build
Date: 2021-04-07 06:00:10
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On 08/03/2021 19:06, Andrey Borodin wrote:
> There were numerous GiST-build-related patches in this thread. Yet uncommitted is a patch with sortsupport routines for btree_gist contrib module.
> Here's its version which needs review.

Reviewing this now again. One thing caught my eye:

> +static int
> +gbt_bit_sort_build_cmp(Datum a, Datum b, SortSupport ssup)
> +{
> + return DatumGetInt32(DirectFunctionCall2(byteacmp,
> + PointerGetDatum(a),
> + PointerGetDatum(b)));
> +}

That doesn't quite match the sort order used by the comparison
functions, gbt_bitlt and such. The comparison functions compare the bits
first, and use the length as a tie-breaker. Using byteacmp() will
compare the "bit length" first. However, gbt_bitcmp() also uses
byteacmp(), so I'm a bit confused. So, huh?

- Heikki

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