Add documentation for usage of PostgreSQL 9.3. Thanks to @bionix

https://github.com/gitlabhq/gitlabhq/pull/7711

database/usage_postgresql_9.3/README.md

@@ -0,0 +1,93 @@
+# Usage of PostgreSQL 9.3
+
+```
+Distribution      : Debian Wheezy
+GitLab version    : 7.x
+Database          : PostgreSQL
+Contributors      : @bionix
+```
+
+This recipe shows how to upgrade the PostrgreSQL database from version 9.1 to 9.3.
+It is **strongly recommended** to take a [backup][] of your GitLab database before
+following the next steps.
+
+## Install PostgreSQL 9.3
+
+Install the [official PostgreSQL Debian/Ubuntu repository][apt]:
+
+    cat >> /etc/apt/sources.list.d/pgdg.list << EOF
+    deb http://apt.postgresql.org/pub/repos/apt/ wheezy-pgdg main
+    EOF
+
+Install the repository signing key:
+
+    sudo apt-get install wget ca-certificates
+    wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
+
+Update your apt lists:
+
+    sudo apt-get update
+
+Upgrade your installed packages:
+
+    sudo apt-get upgrade
+
+## Intregation in the manual installation process
+
+If you arrive the point 4 in the manual [4. Database][db-manual], replace the
+first step with the following command:
+
+    sudo apt-get install -y postgresql-9.3 postgresql-client-9.3 libpq-dev
+
+After that, follow the normal manual instructions.
+
+## Upgrade from PostgreSQL version 9.1 to 9.3
+
+Stop your Gitlab service:
+
+    sudo service gitlab stop
+
+Install all PostgreSQL packages for your environment:
+
+    sudo apt-get install -y postgresql-9.3 postgresql-server-dev-9.3 postgresql-contrib-9.3 postgresql-client-9.3 libpq-dev
+
+Extend your PostgreSQL 9.3. server with your extensions:
+
+    sudo su - postgres -c "psql template1 -p 5433 -c 'CREATE EXTENSION IF NOT EXISTS hstore;'"
+    sudo su - postgres -c "psql template1 -p 5433 -c 'CREATE EXTENSION IF NOT EXISTS \"uuid-ossp\";'"
+
+Stop your PostgreSQL server daemons (both!):
+
+    sudo service postgresql stop
+
+Make the migration from 9.1 to 9.3:
+
+    sudo su - postgres -c '/usr/lib/postgresql/9.3/bin/pg_upgrade \
+                            -b /usr/lib/postgresql/9.1/bin \
+                            -B /usr/lib/postgresql/9.3/bin \
+                            -d /var/lib/postgresql/9.1/main/ \
+                            -D /var/lib/postgresql/9.3/main/ \
+                            -O " -c config_file=/etc/postgresql/9.3/main/postgresql.conf" \
+                            -o " -c config_file=/etc/postgresql/9.1/main/postgresql.conf"'
+
+Remove your old PostgreSQL version, if you have no issues:
+
+    sudo apt-get remove -y postgresql-9.1
+
+Change the listen port of your PostgreSQL 9.3 server:
+
+    sudo sed -i "s:5433:5432:g" /etc/postgresql/9.3/main/postgresql.conf
+
+Start your PostgreSQL service:
+
+    sudo service postgresql start
+
+Start your Gitlab service:
+
+    sudo service gitlab start
+
+Done!
+
+[backup]: http://doc.gitlab.com/ce/raketasks/backup_restore.html
+[apt]: https://wiki.postgresql.org/wiki/Apt
+[db-manual]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/install/installation.md#4-database