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1. PDP would implement the pub-sub for policies per each component
   1. maintain the database of subscribers with the
      1. list of generic policy-filters (==resource from the request json to /decision/v1 API) and the
      2. subscriber_topic for Message Router of DMaaP that uniquely identifies the component instance like “policies_DCAE_tca_<service-component-name>”
   2. on policy-update/add/remove, the PDP would iterate through the subscribers and do its matching to any of the policy-filters on each subscriber the same way as /decision/v1 does
      
   3. if policy-update/add/remove matches any of the policy-filters, PDP would push the policy-update notification that contains the whole policy-body of each added/updated policy and policy-id of each removed policy to Message Router of DMaaP with the topic that uniquely identifies the component instance like “policies_DCAE_tca_<service-component-name>”=subscriber_topic
   4. there might be a need for some logic to identify the stale subscriptions by checking with the Message Router of DMaaP on the timestamps of the latest delivered/undelivered message per ach topic PDP has the subscription on
2. Message Router of DMaaP will do the following
   
   1. persistently (up to 7 days) deliver all the policy-update notifications per per subscriber_topic
   2. component will listen for the subscriber_topic of the policy-update notification from MR of DMaaP with long-collect-polling time like 15 seconds to grab the push notification
3. Component instance would do the following
   1. on startup – subscribe to PDP with the policy-filter the component is interested in and the DMaaP topic that would uniquely identify the component instance like subscriber_topic=“policies_DCAE_tca_<service-component-name>” that that uniquely identifies the component instance
   2. listen for topic “policies_DCAE_tca_<service-component-name>” subscriber_topic of policy-update notification from MR of DMaaP with long-collect-polling time like 15 seconds to grab the push notification
      
      1. on receiving the policy-update pushed notification from DMaaP, handle the policy-update that contains the whole policy-body of each added/updated policy and policy-id of each removed policy
   3. on stop,
unsubscribe
4. 1. unsubscribe subscriber_topic from PDP

See inside the diagram for more details, data structures, and flow steps

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