Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at> writes:
> The usesysid was originally intended to map pg users to unix accounts.
> I do not see why it should not be possible to map different pg users
> to a single unix account. The above imho stems from an improper use of this
> column which needs to be fixed, not the column made unique.
No. I'm not sure whether or not I believe the comment about Unix
accounts; Postgres does not care about Unix accounts, and never has
to my knowledge. But it has always used the usesysid as owner
identification for database objects (tables etc). If two different
users have the same usesysid then they are both the owner of these
objects; moreover they are interchangeable for permissions checks, too.
This is not a situation that has any practical use AFAICS.
There has been some talk of eliminating usesysid entirely in favor of
using the OID of the pg_shadow entry as the user's ID for ownership
identification. If that happens, we'd want a unique index on OID
instead.
regards, tom lane