Aleksander Alekseev <aleksander(at)timescale(dot)com> writes:
> One thing that I couldn't immediately figure out is why 0 hash value
> is treated as a magic invalid value in TypeCacheTypCallback():
I've not read this patch, but IIRC in some places we have a convention
that hash value zero is passed for an sinval reset event (that is,
"flush all cache entries").
regards, tom lane