Analyzes how well a candidate shard key would distribute a collection across the shards of a cluster. Analyzing a shard key samples documents on a live cluster and does not finish within one request, so it is submitted as a long-running operation: the request returns an operation to poll, and the completed analysis is a separate resource that the operation links to. To receive the most common shard key values, you must have the Project Data Access Read Only role or higher. Otherwise, MongoDB Cloud omits those values, because they come from the collection's data rather than from statistics about it.