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) .
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 ?
I don't think the record on the page is rewritten in a more compact form. Even if it were, the page would just have a small hole in it.
A different version of this question might be whether the tuple is deleted and then the hopefully smaller row inserted some where else when "UPDATE example SET datecreation = NULL;" is executed. But of course then you'd use more disk space, since now the file(s) will be full of holes. Vacuum will clean them up so that new data can be inserted there, but the files would not be shrunk.