Re: Columns in pg_shadow?

"Michael A. Mayo" <mmayo(at)mcauleybrooklyn(dot)org> writes:
> I have been looking for information on the meaning of each column in
> pg_shadow, but have been unable to find any thus far. It would be good if
> someone could enlighten me, or point me to existing documentation. The
> columns I am unsure of are listed below:

> usecreatedb:
> Ability to create new databases?

Check.

> usetrace:
> ?

Searching through the sources shows that this flag is not used anywhere.
The catalogs.sgml doc file defines it as "can user set trace flags?"
but whatever code it controlled must be long dead...

> usesuper:
> I assume this makes the user a "superuser," but I am not sure exactly
> what that means.

A superuser is God as far as the database is concerned: she's not
subject to any protection checks, and there are some security-critical
operations like backend COPY that are only allowed to superusers.
Pretty much the same concept as being "root" on a Unix system.

> usecatupd:
> Ability to change system tables?

Right. The point of this flag is to let superusers be slightly less
Godlike: by turning off her usecatupd flag, a superuser can revoke her
right to alter system tables via direct INSERT/UPDATE/DELETE commands,
and thereby avoid foolish mistakes. Or that seemed to be the plan
anyway. Since there's no really convenient interface for twiddling
this flag, I doubt anyone actually bothers to change it. It starts
out the same as one's usesuper flag, and probably stays that way...

BTW, the easiest way to learn about this sort of stuff is to scan the
source code --- and if you don't have a handy tool for that, allow me
to recommend "glimpse", http://glimpse.cs.arizona.edu/. I wasn't
too sure about usetrace or usecatupd either, but it took just a few
seconds to examine their uses and learn what I said above. (For fans of
the One True Editor: I have an emacs macro that invokes glimpse in the
same way as grep is called by the standard "grep" macro, so that you can
step through all the hits with C-x `. Let me know if you need it.)

regards, tom lane