PostgreSQL是自由的对象-关系型数据库服务器（数据库管理系统），在灵活的BSD-风格许可证下发行。

可查看官网教程添加源安装。

下面以Debian8 jessie为例，安装PostgreSQL 9.5（Debian仓库内的PostgreSQL是9.4的）

添加源：

echo "deb http://apt.postgresql.org/pub/repos/apt/ jessie-pgdg main" > /etc/apt/sources.list.d/pgdg.list

导入密钥：

wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | \
sudo apt-key add -
sudo apt-get update
sudo apt-get install postgresql-9.5

添加新用户：

sudo -i -u postgres
createuser --interactive

由于Ubuntu 14.04官方源内的PostgreSQL是9.3的，如果已经有数据，升级到9.4时要做以下步骤：

Thanks: Upgrading PostgreSQL from 9.3 to 9.4 when upgrading Ubuntu 14.04 to 14.10

要求：同时安装9.3和9.4的PostgreSQL

0. 先备份数据

$ pg_dumpall > backup.sql

1. 运行pg_lsclusters，保证9.3和9.4都启动了。

$ pg_lsclusters 
Ver Cluster Port Status Owner    Data directory               Log file
9.3 main    5432 online postgres /var/lib/postgresql/9.3/main /var/log/postgresql/postgresql-9.3-main.log
9.4 main    5433 online postgres /var/lib/postgresql/9.4/main /var/log/postgresql/postgresql-9.4-main.log

2. 暂停9.4

sudo pg_dropcluster 9.4 main --stop

3. 迁移9.3数据到最新版本

sudo pg_upgradecluster 9.3 main

4. 此时9.3数据库应该停止stop了

$ pg_lsclusters
Ver Cluster Port Status Owner    Data directory               Log file
9.3 main    5433 down   postgres /var/lib/postgresql/9.3/main /var/log/postgresql/postgresql-9.3-main.log
9.4 main    5432 online postgres /var/lib/postgresql/9.4/main /var/log/postgresql/postgresql-9.4-main.log

5. 移除9.3

sudo pg_dropcluster 9.3 main
sudo aptitude remove postgresql-9.3 postgresql-client-9.3

Visit PostgreSQL Yum Repository and select PostgreSQL version, download repo rpm like this:

wget https://download.postgresql.org/pub/repos/yum/9.5/redhat/rhel-6-x86_64/pgdg-centos95-9.5-3.noarch.rpm
yum install postgresql95 postgresql95-devel postgresql95-libs postgresql95-server

Change user password:

sudo -u postgres psql
 
# psql shell
\password <user>

Set user as supersuer:

sudo -u postgres psql -c "ALTER USER <user> with superuser"

Show size of every PostgreSQL database.[(https://www.peterbe.com/plog/show-size-of-every-postgresql-database)]

First, connect to postgres database:

psql postgres

Then run SQL:

SELECT pg_database.datname, 
  pg_database_size(pg_database.datname), 
  pg_size_pretty(pg_database_size(pg_database.datname)) 
FROM pg_database ORDER BY 2 DESC;

复用连接可提高数据库的性能，详见PgBouncer