apt-cache policy postgresql
postgresql:
  Installed: 9.1+129ubuntu1
  Candidate: 9.1+129ubuntu1
  Version table:
 *** 9.1+129ubuntu1 0
        500 http://nova.clouds.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     9.1+129 0
        500 http://nova.clouds.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages