Re: How much size saved by updating column to NULL ?

On Friday, January 12, 2024, Sébastien TANIERE <seb(dot)taniere(at)gmail(dot)com>
wrote:

> Hello,
> in my company, some columns rarely used in a PG database 14.8 have been
> set to NULL in order to save disk space (datecreation & acteurcreation in
> following table) .
>
> create table example
> (
> id varchar(25) not null,
> datecreation timestamp(6),
> acteurcreation varchar(50),
> valeurunit smallint
> )
>
> I am wondering if it is really useful for every type of column.
> Intuitively, i would say that it does not save space for fixed field
> datecreation as it is a fixed size column.
>
> Do we save 8 bytes by timestamp column updated to NULL or not ?
>
>
You probably should just measure it yourself. But yes, the representation
of null in a tuple is the absence of data and a bit in the nulls bitmap.
So there is overhead but also savings. The net effect is case specific.

David J.