This document provides answers to frequently asked questions about how metrics work in the ExtraHop system.
On the Dashboard page, you can configure charts to display either top-level or detail metrics. On protocol pages, you can view top-level metrics and then drill down to view detail metrics.
A top-level, or base, metric gives you a sum of data for a specified time period. The ExtraHop system provides you with real-time updates about top-level metrics. For example, you can view the total number of HTTP requests sent by a device for the last 30 minutes.
In the following figure, a bar chart displays the top-level metric for the total number of HTTP requests that were sent to a web server during a specific time period.
Detail metrics provide you with a metric value for a specific key, such as a client IP address, server IP address, URI, hostname, referrer, certificate, or method. For example, you can drill down on the total number of HTTP requests to break out the number of requests sent per client. When you drill down, the ExtraHop system provides you with a topnset of detail metrics. A topnset is the top 1,000 key-value pairs calculated for the time interval you specify in the Time Selector. A topnset is not a complete data set because a topnset only represents the key-values that are recorded for a specific aggregation roll up (based on a specified time interval), and is limited to up to 1,000 keys per topnset.
In the following figure, a Bar chart displays detail metric values by client (which is a key) after drilling down on the top-level metric for HTTP requests. Specifically, the chart displays eight clients that sent the most requests to the web server during a specific time period. You can configure charts to show you either a specific key or a specific number of keys from a topnset.
|Note:||When drilling down to detail metrics from protocol pages, you might encounter a chart that includes more than 1,000 keys. Some charts in the ExtraHop system combine topnsets for multiple detail metrics into one table. You can then sort keys by detail metrics. For example, when you drill down on the responses metric by URI from the Metrics > Applications > All Activity > Web page, the chart displays both a topnset of URIs for HTTP Responses and a topnset of URIs for Server Processing Time.|