Why did PostgreSQL merge users and groups into roles?

Question

From the PostgreSQL docs:

The concept of roles subsumes the concepts of \"users\" and \"groups\". In PostgreSQL versions before 8.1, users and group

Answer 1

Having a distinction between users and groups doesn't gain you anything.

AFAIK the motivation for changing it was to simplify uses like:

• One user masquerading as another, eg a superuser simulating a reduced permissions user. With unified roles this becomes just another change of current role, no different to changing primary group.

• Groups that are members of other groups to implement granular access permissions.

If you want the details, though, you're best off checking out the archives of the pgsql-hackers list for the period, and the git history (converted from CVS).