Re: UUID's as primary keys

On Wed, Jun 28, 2006 at 10:22:45AM +0200, Thomas Hallgren wrote:
> Thanks. That would of course work but at the same time it increases the
> complexity of my app. Yet another component to install and keep track
> of. It's also a bit of an overkill since the only thing I need is an
> opaque bit storage. Why is it that PostgreSQL lack a fixed length binary
> type similar to the RAW type in Oracle? ISTM that could be very useful
> and not very hard to implement.

AIUI, it can't be done because of a basic rule of the type system: the
typmod can't be necessary to interpret the binary representation of a
value. For something like RAW(16) the type would be the oid for "raw"
and the typmod would be 16. However, when reading the value from a disk
page, you're not given the typmod, so you have no way of determining
the length.

That's why there is a verlena header for types where you don't know the
length, which adds overhead. The alternative is to create a type of the
exact length you want, but in your case that's not acceptable either.

I'm not sure if there are any other alternatives.

Have a ncie day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.