How much size saved by updating column to NULL ?

[Sébastien TANIERE <seb.taniere@xxxxxxxxx>]

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 ?

Have a good day

Sébastien TANIERE