Re: Object like pg_class.relkind = 's' or 'c' have on-disk file?

"Qingqing Zhou" <zhouqq@cs.toronto.edu> writes:
> Pg_xactlock is always there as a special relation.

pg_xactlock isn't really a relation.  The way I think about it is that
it's a dummy entry in pg_class that exists to reserve a relation OID
for a specific purpose --- namely, we can lock transaction IDs by
locking what would otherwise be a page of that relation.

There was some talk recently about reorganizing the locktag design
so that transaction lock tags would be clearly distinguishable from
any lock associated with a relation.  If we got that done, there'd
be no need for the pg_xactlock entry at all.

> I am not sure about 'c'.

'c' entries in pg_class are for composite types.  They don't have
any associated disk storage either.

            regards, tom lane