Re: wrong query results on bf leafhopper

is there different tables "Seq Scan on tenk1 t2" and "Seq Scan on tenk1 
t1", so it might not be a bug, isn't it?

On 16.05.2025 09:19, Andres Freund wrote:
> Hi,
>
> I noticed this recent BF failure:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=leafhopper&dt=2025-05-15%2008%3A10%3A04
>
> === dumping /home/bf/proj/bf/build-farm-17/HEAD/pgsql.build/src/test/recovery/tmp_check/regression.diffs ===
> diff -U3 /home/bf/proj/bf/build-farm-17/HEAD/pgsql.build/src/test/regress/expected/memoize.out /home/bf/proj/bf/build-farm-17/HEAD/pgsql.build/src/test/recovery/tmp_check/results/memoize.out
> --- /home/bf/proj/bf/build-farm-17/HEAD/pgsql.build/src/test/regress/expected/memoize.out	2025-05-15 08:10:04.211926695 +0000
> +++ /home/bf/proj/bf/build-farm-17/HEAD/pgsql.build/src/test/recovery/tmp_check/results/memoize.out	2025-05-15 08:18:29.117733601 +0000
> @@ -42,7 +42,7 @@
>      ->  Nested Loop (actual rows=1000.00 loops=N)
>            ->  Seq Scan on tenk1 t2 (actual rows=1000.00 loops=N)
>                  Filter: (unique1 < 1000)
> -               Rows Removed by Filter: 9000
> +               Rows Removed by Filter: 8982
>            ->  Memoize (actual rows=1.00 loops=N)
>                  Cache Key: t2.twenty
>                  Cache Mode: logical
> @@ -178,7 +178,7 @@
>      ->  Nested Loop (actual rows=1000.00 loops=N)
>            ->  Seq Scan on tenk1 t1 (actual rows=1000.00 loops=N)
>                  Filter: (unique1 < 1000)
> -               Rows Removed by Filter: 9000
> +               Rows Removed by Filter: 8981
>            ->  Memoize (actual rows=1.00 loops=N)
>                  Cache Key: t1.two, t1.twenty
>                  Cache Mode: binary
>
>
> For a moment I thought this could be a bug in memoize, but that doesn't
> actually make sense - the failure isn't in memoize, it's the seqscan.
>
> Subsequently I got worried that this is an AIO bug or such causing wrong query
> results. But there are instances of this error well before AIO was
> merged. E.g.
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=leafhopper&dt=2024-12-18%2023%3A35%3A04
>
> The same error is also present down to 16.
>
> In 15, I saw a potentially related error
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=leafhopper&dt=2024-12-16%2023%3A43%3A03
>
>
> There have been other odd things on leafhopper, see e.g.:
> https://www.postgresql.org/message-id/35d87371-f3ab-42c8-9aac-bb39ab5bd987%40gmail.com
> https://postgr.es/m/Z4npAKvchWzKfb_r%40paquier.xyz
>
> Greetings,
>
> Andres Freund
>
>
-- 
Regards,
Alena Rybakina
Postgres Professional