Below URLs explains the policy/session logging configuration.
http://kb.juniper.net/InfoCenter/index?page=content&id=KB16509&actp=search
http://kb.juniper.net/InfoCenter/index?page=content&id=KB16506&actp=search
http://kb.juniper.net/InfoCenter/index?page=content&id=KB29539&actp=search
http://kb.juniper.net/InfoCenter/index?page=content&id=KB16224&actp=search
http://www.juniper.net/documentation/en_US/junos12.3/topics/task/operational/chassis-cluster-srx-log-message-configuring.html
http://kb.juniper.net/InfoCenter/index?page=content&id=KB16509&actp=search
http://kb.juniper.net/InfoCenter/index?page=content&id=KB16506&actp=search
http://kb.juniper.net/InfoCenter/index?page=content&id=KB29539&actp=search
http://kb.juniper.net/InfoCenter/index?page=content&id=KB16224&actp=search
http://www.juniper.net/documentation/en_US/junos12.3/topics/task/operational/chassis-cluster-srx-log-message-configuring.html