The refresh queue is ITSI's task management system that use the KV Store & Splunk's storage layer to manage your ITSI environment & thus maintaining consistency across the board.
The refresh queue runs and maintains a lot of jobs that check if a given user intearction will have an impact on the environment, and if a user-triggered change is deemed to be impactful to the environment by the reshresh queue, the refresh queue will pick that change request up, assess its impact and THEN commit those changes to the KV Store for the user to see the changes and then delete the change job request from the queue.
To give you an idea, below are a couple of jobs that the refresh queue handles (chanes that could effect your environment as you can telll by the names): service_dependency_changed
For example, if user commits a job to delete a service, the delete_service job is triggered and the refresh queue will do housekeeping tasks to ensure that the requested change does not ruin the environment, updates that object in the KV store (deleting it from KV store in this example), and then concluldes the job by deleting the chanage job from the refresh queue.
In other words, the refresh queue ensures data integrity and eventual consistency of your ITSI configuration.