Configuring and Starting the PostgreSQL Server

By default, PostgreSQL only accepts connections on the loopback interface. You must reconfigure PostgreSQL to accept connections from the fully qualified domain names (FQDN) of the hosts hosting the services for which you are configuring databases. If you do not make these changes, the services cannot connect to and use the database on which they depend.

If you are making changes to an existing database, make sure to stop any services that use the database before continuing.

Make sure that LC_ALL is set to en_US.UTF-8 and initialize the database as follows:

RHEL 7:

echo 'LC_ALL="en_US.UTF-8"' >> /etc/locale.conf
sudo su -l postgres -c "postgresql-setup initdb"

SLES 12:

sudo su -l postgres -c "initdb --pgdata=/var/lib/pgsql/data --encoding=UTF-8"

Ubuntu:
```
sudo service postgresql start
```

Enable MD5 authentication. Edit pg_hba.conf, which is usually found in /var/lib/pgsql/data or /etc/postgresql/<version>/main. Add the following line:
```
host all all 127.0.0.1/32 md5
```
If the default pg_hba.conf file contains the following line:
```
host all all 127.0.0.1/32 ident
```
then the host line specifying md5 authentication shown above must be inserted before this ident line. Failure to do so may cause an authentication error when running the scm_prepare_database.sh script. You can modify the contents of the md5 line shown above to support different configurations. For example, if you want to access PostgreSQL from a different host, replace 127.0.0.1 with your IP address and update postgresql.conf, which is typically found in the same place as pg_hba.conf, to include:
```
listen_addresses = '*'
```
Configure settings to ensure your system performs as expected. Update these settings in the /var/lib/pgsql/data/postgresql.conf or /var/lib/postgresql/data/postgresql.conf file. Settings vary based on cluster size and resources as follows:
- Small to mid-sized clusters - Consider the following settings as starting points. If resources are limited, consider reducing the buffer sizes and checkpoint segments further. Ongoing tuning may be required based on each host's resource utilization. For example, if the Cloudera Manager Server is running on the same host as other roles, the following values may be acceptable:
  - max_connection - In general, allow each database on a host 100 maximum connections and then add 50 extra connections. You may have to increase the system resources available to PostgreSQL, as described at Connection Settings.
  - shared_buffers - 256MB
  - wal_buffers - 8MB
  - checkpoint_segments - 16
    note
    The checkpoint_segments setting is removed in PostgreSQL 9.5 and higher, replaced by min_wal_size and max_wal_size. The PostgreSQL 9.5 release notes provides the following formula for determining the new settings:
    max_wal_size = (3 * checkpoint_segments) * 16MB
  - checkpoint_completion_target - 0.9
- Large clusters - Can contain up to 1000 hosts. Consider the following settings as starting points.
  - max_connection - For large clusters, each database is typically hosted on a different host. In general, allow each database on a host 100 maximum connections and then add 50 extra connections. You may have to increase the system resources available to PostgreSQL, as described at Connection Settings.
  - shared_buffers - 1024 MB. This requires that the operating system can allocate sufficient shared memory. See PostgreSQL information on Managing Kernel Resources for more information on setting kernel resources.
  - wal_buffers - 16 MB. This value is derived from the shared_buffers value. Setting wal_buffers to be approximately 3% of shared_buffers up to a maximum of approximately 16 MB is sufficient in most cases.
  - checkpoint_segments - 128. The PostgreSQL Tuning Guide recommends values between 32 and 256 for write-intensive systems, such as this one.
    note
    The checkpoint_segments setting is removed in PostgreSQL 9.5 and higher, replaced by min_wal_size and max_wal_size. The PostgreSQL 9.5 Release Notes provides the following formula for determining the new settings:
    max_wal_size = (3 * checkpoint_segments) * 16MB
  - checkpoint_completion_target - 0.9.

Configure the PostgreSQL server to start at boot.


OS	Command
RHEL 7 compatible	`sudo systemctl enable postgresql`

Restart the PostgreSQL database:
- RHEL 7 Compatible:
```
sudo systemctl restart postgresql
```

Creating Databases for Cloudera Software

You must create databases and service accounts for components that require databases.

The following components require databases:

Cloudera Manager Server
Cloudera Management Service roles:
- Reports Manager
Data Analytics Studio (DAS) Supported with PostgreSQL only.
Hue
Each Hive metastore
Oozie
Data Analytics Studio
Schema Registry
Streams Messaging Manager

The databases must be configured to support the PostgreSQL UTF8 character set encoding.

Record the values you enter for database names, usernames, and passwords. The Cloudera Manager installation wizard requires this information to correctly connect to these databases.

To create databases for Cloudera Manager Server, Cloudera Management Service roles, Activity Monitor, Reports Manager, Hue, Hive metastores, Oozie, and DAS, complete the following steps:

Connect to PostgreSQL:
```
sudo -u postgres psql
```

Create databases for each service you are using from the below table:

CREATE ROLE <user> LOGIN PASSWORD '<password>';

CREATE DATABASE <database> OWNER <user> ENCODING 'UTF8';

You can use any value you want for <database>, <user>, and <password>. The following examples are the default names provided in the Cloudera Manager configuration settings, but you are not required to use them:

Table 1. Databases for Cloudera Software
Service	Database	User
Cloudera Manager Server	scm	scm
Reports Manager	rman	rman
Hue	hue	hue
Hive Metastore Server	metastore	hive
Oozie	oozie	oozie
Data Analytics Studio (DAS) Supported with PostgreSQL only.	das	das
Schema Registry	schemaregistry	schemaregistry
Streams Messaging Manager	smm	smm

Record the databases, usernames, and passwords chosen because you will need them later.

For PostgreSQL 8.4 and higher, set standard_conforming_strings=off for the Hive Metastore and Oozie databases:
```
ALTER DATABASE <database> SET standard_conforming_strings=off;
```

If you plan to use Apache Ranger, see the following topic for instructions on creating and configuring the Ranger database. See Configuring a PostgreSQL Database for Ranger.
If you plan to use Schema Registry or Streams Messaging Manager, see the following topic for instructions on configuring the database: Configuring the Database for Streaming Components
After you install and configure PostgreSQL databases for Cloudera software, continue to Step 5: Set up the Cloudera Manager Database to configure a database for Cloudera Manager.