To configure Oozie to use PostgreSQL, add the following property to in the oozie-site.xml:
<property>
        <name>oozie.service.JPAService.jdbc.driver</name>
        <value>org.postgresql.Driver</value>
    </property>
    <property>
        <name>oozie.service.JPAService.jdbc.url</name>
        <value>jdbc:postgresql://localhost:5432/oozie</value>
    </property>
    <property>
        <name>oozie.service.JPAService.jdbc.username</name>
        <value>oozie</value>
    </property>
    <property>
        <name>oozie.service.JPAService.jdbc.password</name>
        <value>oozie</value>
    </property>