RE: error "can only drop stats once" brings down database

> Floris Van Nee <florisvannee@Optiver.com> writes:
> > Hi,
> > On a database we have we've recently seen a fatal error occur twice. The
> error happened on two different physical replicas (of the same cluster)
> during a WAL redo action in the recovery process. They're running Postgres
> 15.5.
>
> > Occurrence 1:
> > 2024-02-01 06:55:54.476 CET,,,70290,,65a29b60.11292,6,,2024-01-13 15:17:04
> CET,1/0,0,FATAL,XX000,"can only drop stats once",,,,,"WAL redo at
> A7BD1/D6F9B6C0 for Transaction/COMMIT: 2024-02-01 06:55:54.395851+01;
> ...
>
> Hmm.  This must be coming from pgstat_drop_entry_internal.
> I suspect the correct fix is in pgstat_drop_entry, along the lines of
>
> -    if (shent)
> +    if (shent && !shent->dropped)
>
> but it's not clear to me how the already-dropped case ought to affect the
> function's bool result.  Also, how are we getting into a concurrent-drop
> situation in recovery?

Anyone has further thoughts on this? This still happens occasionally.

-Floris