Why RHEV-M is not able to access with error Could not get JDBC Connection ?

Issue

• RHEV-M portal is inaccessible and showing internal engine error
• Any api operation to the RHEV-M is failing with internal engine error
• Below error is logged in the engine log:

Caused by: org.springframework.jdbc.support.MetaDataAccessException: Could not get Connection for extracting meta data; nested exception is org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: javax.resource.ResourceException: IJ000453: Unable to get managed connection for java:/ENGINEDataSource
2016-02-04 12:38:08,527 ERROR [org.ovirt.engine.core.bll.SearchQuery] (ajp-/127.0.0.1:8702-9) Query SearchQuery failed. Exception message is Could not get JDBC Connection; nested exception is java.sql.SQLException: javax.resource.ResourceException: IJ000453: Unable to get managed connection for java:/ENGINEDataSource : org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: javax.resource.ResourceException: IJ000453: Unable to get managed connection for java:/ENGINEDataSource: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: javax.resource.ResourceException: IJ000453: Unable to get managed connection for java:/ENGINEDataSource