Which of the following is not a metric available in Azure Cognitive Search?

The correct choice indicates that "Count of active users" is not a metric available in Azure Cognitive Search. This is because Azure Cognitive Search focuses on the performance and efficiency metrics directly related to the search capabilities, such as the responsiveness of the search service, query throughput, and the overall health and optimization of the search index.

Metrics like search latency, count of queries per second, and percentage of throttled queries provide essential insights into the service's performance and usage patterns. Search latency measures how quickly the search service can respond to a query, while the count of queries per second helps assess the load and efficiency of the system. The percentage of throttled queries reflects the number of queries that could not be processed due to service limits, which is crucial for managing and optimizing the service capacity.

However, the count of active users deals more with usage statistics that aren't measured by Azure Cognitive Search. It does not provide direct insights into the search functionality or operational effectiveness, which is a more relevant focus for the metrics available in Azure Cognitive Search.