Now that we have both Prometheus and Grafana logging metrics, let's try out some queries. I won't be able to give you a full rundown on every aspect of PromQL—the Prometheus query language—but I can help you to learn enough to be able to examine many of the server metrics that can be accessed from the Prometheus data source.
To get a better understanding of how queries work in time-series databases such as Prometheus, let's first start with a more traditional database, such as MySQL. Typically, the structure of a query looks something like this:
SELECT some fields
FROM some table
WHERE fields match some criteria
You get back from the query some rows, each one containing the contents of some fields. In the case of time-series databases, things work a little differently. The query has a form that is more like the following:
SELECT metric
FROM some data store
WHERE metric tags match some...