Re: Yet another fast GiST build

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Heikki Linnakangas <hlinnaka(at)gmail(dot)com>, 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>
Subject: Re: Yet another fast GiST build
Date: 2021-01-13 18:16:23
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On 13 January 2021 20:04:10 EET, Heikki Linnakangas <hlinnaka(at)gmail(dot)com> wrote:
>On 13 January 2021 13:53:39 EET, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>>Looks like the LSN on the page is not set to GistBuildLSN as expected.
>>Thorntail is a sparc64 system, so little-endian, but the other
>>little-endian buildfarm members are not reporting this error. Any idea
>>what might be going on?
>Status update on this: I am building Postgres in a qemu sparc64 emulated virtual machine, hoping to be able to reproduce this. It's very slow, so it will take hours still to complete.
>I don't think this is a problem with the test, or with the new pageinspect functions, but a genuine bug in the gist building code. Or there is something special on that animal that causes the just-created index pages to be dirtied. It does seem to happen consistently on thorntail, but not on other animals.

Ah, silly me. Thorntail uses "wal_level=minimal". With that, I can readily reproduce this.

I'm still not sure why it happens, but now it should be straightforward to debug.

- Heikki

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