title: PostgreSQL user groups and authorization
body: <p>Postgresql version 9.0</p>
  
  <p>I need an idea for grouping postgresql users.</p>
  
  <p>i have 150+ table in database, and i want to settle groups of people. some of them can reach all tables, some of them not. 
  I know it is possible to make it using grant or creating roles. but i want to figure out which is the best way to do that. how will it effect the performance?</p>
  
  <p>giving all users to access some of the tables and managing them seems hard to me. so i thought what about creating different tablespaces and set permissions by tablespace. </p>
  
  <p>is there any good tutorial , article or approach for creating user groups? what is your advice?</p>