Re: Physical column size

On Fri, Mar 03, 2006 at 11:03:24AM +0100, Paul Mackay wrote:
> The end result is that the physical size on disk used by table tmp_A is
> exactly the same as table tmp_B (as revealed by the pg_relation_size
> function) ! Given that a "char" field is supposed to be 1 byte in size and a
> int4 4 bytes, shouldn't the tmp_A use a smaller disk space ? Or is it that
> any value, whatever the type, requires at least 4 bytes to be stored ?

Alignment. An int4 value must start on a multiple of 4 offset, so you
get three bytes of padding. If you put the int4, then the char it
should work better. Although whole rows have alignment requirements
too...

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.