Bruce Momjian <maillist@candle.pha.pa.us> writes:
> Zero overhead for types that don't use it is meaningless, because the
> varlena length is 4 bytes, while current atttypmod is only two. Second,
> I don't see how a varlena makes atttypmod less type-specific.
Well, the issue is making sure that it will be adequate for future
datatypes that we can't foresee.
I can see that a variable-size atttypmod might be a tad painful to
support. If you don't want to go that far, a reasonable compromise
would be to make it int4 instead of int2. int2 is already uncomfortably
tight for the numeric/decimal datatypes, which we surely will want to
support soon (at least I do ;-)). int4 should give a little breathing
room for datatypes that need to encode more than one subfield into
atttypmod.
regards, tom lane