UI can experience slowness if all appfabric-executor threads are occupied.
AppFabric by default has 20 (appfabric-executor) threads for handling http requests. These threads handle requests from REST api directly as well as API requests from UI. Any custom developed tool to get operational metadata calling these REST api can easily occupy all those 20 threads, causing high priority UI requests to be delayed.
We should look into assigning some priority to the api requests so that UI requests (interactive) will always have high priority over direct REST api calls.