Re: TODO Item - Return compressed length of TOAST datatypes (WIP)

Mark Kirkwood <markir@paradise.net.nz> writes:
> I thought I would have a look at:
> (Datatypes) Add function to return compressed length of TOAST data values.

My recollection of that discussion is that we just wanted something
that would return the actual VARSIZE() of the datum.  You're building
something way too confusing ...

A more interesting point is that the way you've declared the function,
it will only work on text values, which is pretty limiting.  Ideally
we'd define this thing as "pg_datum_length(any-varlena-type) returns int"
but there is no pseudotype corresponding to "any varlena type".

I was thinking about this the other day in connection with my proposal
to make something that could return the TOAST value OID of an
out-of-line datum.  I think the only non-restrictive way to do it would
be to declare the function as taking "any", and then add a runtime check
using the get_fn_expr_argtype() mechanism to test that what you've been
given is in fact a varlena datatype.

            regards, tom lane