If you have topics with no subscriptions, and if the subscriptions were from Durable subscribers, you may notice they are still receiving messages even if there are no active subscriptions. This behavior may be undesirable when you don't want the subscriptions to receive any more messages, such as after an upgrade.
When the launcher starts, two Durable subscriptions are generated to maintain communication between the Agent & the Server, after which the subscriptions are visible in the subscriptions list, and the same subscription gets reused on restart.
The other condition when this gets generated is if you delete the subscriptions when the Durable subscriber is disconnected, and the subscriber comes back online. The notification and stats messages are sent to the topic to maintain the communication. If a launcher no longer exists or is offline, you may see the disconnected durable subscriptions until the subscriptions are deleted.
Since subscriptions are re-used, a new pair of subscriptions will not be generated on every restart. It is safe to delete the subscriptions if the subscribers will not be started again.
The size of SonicMQStore will increase as the messages for disconnected durable subscriptions needs to be stored in pubsub.odb and you may want to check the size limits set for the store to ensure that no other messages are lost.