Increasing the maximum number of processes for Oracle database

While using Oracle as a backend database for Hue, if you face issues connecting to the Hue service after restarting the database, then it is possible that the Hue is not able to get a new database connection. The following error in the Hue logs indicates that the maximum number of connections have exhausted: "ORA-12519: TNS:no appropriate service handler found". This can be resolved by increasing the number of available processes.

After restarting the Oracle database, if you are not able to connect to the Hue service, check the Hue logs for the "ORA-12519: TNS:no appropriate service handler found" error. The Hue logs are present in the following directory:

opt/cloudera/parcels/CDH-[***VERSION***]/lib/hue/build/env/lib/python2.7/site-packages/Django-1.11.20-py2.7.egg/django/db/backends/oracle/base.py

If you see the above error in the logs, then work with your database admin to check whether the maximum number of processes have exceeded or not. If the maximum number of processes have exceeded, then you will see the following error: "ORA-00020: maximum number of processes exceeded". Increase the number of processes to resolve this issue.

How to calculate the number of database processes, transactions, and sessions?

Cloudera recommends that you allow 100 maximum connections for each service that requires a database and then add 50 extra connections. For example, for two services, set the maximum connections to 250. If you have five services that require a database on one host (the databases for Cloudera Manager Server, Activity Monitor, Reports Manager, Cloudera Navigator, and Hive metastore), set the maximum connections to 550.

From the maximum number of connections, you can determine the number of anticipated sessions using the following formula: 
sessions = (1.1 * maximum_connections) + 5

For example, if a host has a database for two services, anticipate 250 maximum connections. If you anticipate a maximum of 250 connections, plan for 280 sessions.

Based on the number of sessions, you can determine the number of anticipated transactions using the following formula: 
transactions = 1.1 * sessions

Continuing with the previous example, if you anticipate 280 sessions, you can plan for 308 transactions.

Work with your Oracle database administrator to apply these derived values to your system.

Using the sample values above, Oracle attributes would be set as follows: 
alter system set processes=250;
alter system set transactions=308;
alter system set sessions=280;