Re: storage size of "bitstring"?

On Sun, Oct 22, 2006 at 06:24:43PM +0200, Alex Mayrhofer wrote:
> Hi,
>
> Two short questions:
>
> 1) What storage size does the "bit(n)" data type have? Is it one byte per 8
> bits (plus a "length" byte)? I didn't find this in neither the docs nor the
> list archives ...

It'll be a varlena structure, see backend/utils/adt/varbit.c. So 4
bytes + space needed for bits.

> 2) Additionally, how much storage space does a functional index which
> returns "boolean" approx. take? Will it be a bitmap?

A boolean is one byte, plus whatever overhead is associated with the
index.

> Reason: i need to add some flags to a row, and i don't want to spend an
> entire byte per flag on a "boolean" column (even worse, new flags could
> probably be added in the future) - would it make sense to use
> a bitstring, together with a functional index on any "interesting" bit in
> that case?

I'd say give it a shot. Seems reasonable.

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.