Re: Yet another fast GiST build

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, 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>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Yet another fast GiST build
Date: 2020-09-20 23:06:09
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Justin Pryzby <pryzby(at)telsasoft(dot)com> writes:
> This also appears to break checksums.

I was wondering about that, because the typical pattern for use of
smgrextend for indexes seems to be

PageSetChecksumInplace(page, lastblock);
smgrextend(rel->rd_smgr, MAIN_FORKNUM, lastblock,, false);

and gist_indexsortbuild wasn't doing either of the first two things.

gist_indexsortbuild_flush_ready_pages looks like it might be
a few bricks shy of a load too. But my local CLOBBER_CACHE_ALWAYS
run hasn't gotten to anything except the pretty-trivial index
made in point.sql, so I don't have evidence about it.

Another interesting point is that all the other index AMs seem to WAL-log
the new page before the smgrextend call, whereas this code is doing it
in the other order. I strongly doubt that both patterns are equally
correct. Could be that the other AMs are in the wrong though.

regards, tom lane

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