Sending the last published items blocks processing EventBus events as it is done on the EventBus threads and requires access to the database. Work requiring access to the database should be moved to a separate thread pool, but filtering (checking if anything needs to be done) should be left on the EventBus threads. That would reduce queue build-up, as EventBus will not be blocked and only filtered events will be queued on the new thread pool.

Additionally, presence from MUC should not be forwarded to PubSub (PEP) for processing, as there should be no need to process them, while they are creating artificial load on the PubSub component.