Re: storage size of "bit" data type..

On Dec 5, 2007, at 14:19 , Alex Mayrhofer wrote:

> Hi,
>
> i'm trying to find out the storage size for bit(n) data. My initial
> assumption would be that for any 8 bits, one byte of storage is
> required.

select pg_column_size(B'1') as "1bit",
pg_column_size(B'1111') as "4bits",
pg_column_size(B'11111111') as "1byte",
pg_column_size(B'111111111111') as "12bits",
pg_column_size(B'1111111111111111') as "2bytes",
pg_column_size(B'11111111111111111') as "17bits",
pg_column_size(B'111111111111111111111111') as "3bytes";
1bit | 4bits | 1byte | 12bits | 2bytes | 17bits | 3bytes
------+-------+-------+--------+--------+--------+--------
9 | 9 | 9 | 10 | 10 | 11 | 11
(1 row)

Looks like there's 8 bytes of overhead as well, probably because a
bit string is a varlena type.

Michael Glaesemann
grzm seespotcode net