Policy Documention Eclipse, PDP-D, Sess Pers

Documentation for Eclipse, PDP-D and Session Persistance.
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Change-Id: I2e988cf5cb64ea60c7173dcd716be5fa25855255
Issue-Id: POLICY-335
Signed-off-by: Saryu Shah <ss3917@att.com>
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+
+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+
+************************************
+Feature: Session Persistence
+************************************
+
+The session persistence feature allows drools kie sessions to be persisted in a database surviving pdp-d restarts.
+
+    .. code-block:: bash
+       :caption: Enable session persistence
+       :linenos:
+
+        policy stop
+        features enable session-persistence
+
+The configuration is located at:
+
+    -  *$POLICY_HOME/config/feature-session-persistence.properties*
+
+Each controller that wants to be started with persistence should contain the following line in its *<controller-name>-controller.properties*
+
+    -  *persistence.type=auto*
+
+    .. code-block:: bash
+       :caption: Start the PDP-D using session-persistence
+       :linenos:
+
+        db-migrator -o upgrade -s ALL
+        policy start
+
+Facts will survive PDP-D restart using the native drools capabilities and introduce a performance overhead.
+
+    .. code-block:: bash
+       :caption: Disable the session-persistence feature
+       :linenos:
+
+        policy stop
+        features disable session-persistence
+        sed -i "/persistence.type=auto/d" <controller-name>-controller.properties 
+        db-migrator -o erase -s sessionpersistence   # delete all its database data (optional)
+        policy start
+
+End of Document
+
+.. SSNote: Wiki page ref. https://wiki.onap.org/display/DW/Feature+Session+Persistence
+
+