Re: Yet another fast GiST build

On 13 January 2021 13:53:39 EET, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>Buildfarm animal thorntail is still not happy:
>
>> --- /home/nm/farm/sparc64_deb10_gcc_64_ubsan/HEAD/pgsql.build/../pgsql/contrib/pageinspect/expected/gist.out 2021-01-13 13:38:09.721752365 +0300
>> +++ /home/nm/farm/sparc64_deb10_gcc_64_ubsan/HEAD/pgsql.build/contrib/pageinspect/results/gist.out 2021-01-13 14:12:21.540046507 +0300
>> @@ -3,21 +3,21 @@
>> CREATE INDEX test_gist_idx ON test_gist USING gist (p);
>> -- Page 0 is the root, the rest are leaf pages
>> SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist_idx', 0));
>> - lsn | nsn | rightlink | flags
>> ------+-----+------------+-------
>> - 0/1 | 0/0 | 4294967295 | {}
>> + lsn | nsn | rightlink | flags
>> +------------+-----+------------+-------
>> + 0/1B8357F8 | 0/0 | 4294967295 | {}
>> (1 row)
>
>Looks like the LSN on the page is not set to GistBuildLSN as expected.
>Weird.
>
>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.

- Heikki