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

Floris Van Nee <florisvannee@Optiver.com> writes:
>> 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.

I was expecting Andres to comment on it eventually.  I don't know
that code well enough to want to modify it on my own authority,
especially not just before a release.

One thing that would be safe enough and perhaps useful is to
modify the "can only drop stats once" message to provide a
little more detail, like the hash key of the problematic
entry.  That might help us understand what's triggering this.
The OIDs would be opaque perhaps, but the PgStat_Kind value
seems useful to know.

            regards, tom lane