@Prudhvi.Athapu if browser client couldn't establish a connection(using websocket which is usual connection establishment immediately after the requestor login), then long polling connection is used. Here message will be sent to the client browser without needing of any request from the client, once the published message in the node finds appropriate subscriptions to this published messages. So messages won't be staying in the server. It will be somehow sent to the client. If we have

Please refer connection topic in the below URL. 

https://docs-previous.pega.com/learning-about-real-time-applications-and-push-notifications-pega-platform

Above explanation is for, we have configured subscription, but user has not logged in or request doesn't reach server. 

If suppose, those messages are not consumed itself, for the performance of disk storage pega keeps messages in kafka cluster for 2.5 days to be available for consuming. This retention period can be changed in prconfig.xml.

Please refer below URL for retention period of kafka Topic messages in cluster. 

https://docs-previous.pega.com/decision-management/87/best-practices-stream-service-configuration