Re: TODO Item - Return compressed length of TOAST datatypes

Tom Lane wrote:
> 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 ...
>

I was guessing a little about exactly what was wanted - for some reason
   I couldn't access the mail archives for the last few days (however,
can now).

> 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.
>

Yes - was thinking I needed to check if the Datum was a varlena (and
didn't know how to do it...), so thanks for the pointer!

With these thoughts in mind, I'll have another go :-)

Cheers

Mark