Re: Yet another fast GiST build

From: "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>
To: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Cc: 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>, Darafei Komяpa Praliaskouski <me(at)komzpa(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Yet another fast GiST build
Date: 2020-09-09 06:43:40
Message-ID: 457812DD-A619-4742-80F3-7EFC7AF6521C@yandex-team.ru
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> 9 сент. 2020 г., в 00:05, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> написал(а):
>
> I've been reviewing the patch today. The biggest changes I've made have been in restructuring the code in gistbuild.c for readability, but there are a bunch of smaller changes throughout. Attached is what I've got so far, squashed into one patch.
Thanks!

> I'm continuing to review it, but a couple of questions so far:
>
> In the gistBuildCallback(), you're skipping the tuple if 'tupleIsAlive == false'. That seems fishy, surely we need to index recently-dead tuples, too. The normal index build path isn't skipping them either.
That's an oversight.
>
> How does the 'sortsupport' routine interact with 'compress'/'decompress'? Which representation is passed to the comparator routine: the original value from the table, the compressed representation, or the decompressed representation? Do the comparetup_index_btree() and readtup_index() routines agree with that?

Currently we pass compressed values, which seems not very good.
But there was a request from PostGIS maintainers to pass values before decompression.
Darafei, please, correct me if I'm wrong. Also can you please provide link on PostGIS B-tree sorting functions?

Thanks!

Best regards, Andrey Borodin.

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