Deciding query step for a given range of timeseries data in a line chart

[dko21]

Hi all, I’m new to the community.

I want to know how Grafana decides on a query step given a time range. E.g. I choose ‘Last 7 days’ on the time filter and not specify a query step, yet - as I saw next to the Query Options - Grafana has a preconfigured or dynamically adjusted query step based on my specified filter. It shows me MD = 400 Interval = 30m from the get-go and the Interval shrinks to 2 seconds as I keep zooming in. I assumed the first 30m and 2 seconds to be the query step in those instances.

In the docs, it says that

Interval - The interval is a time span that you can use when aggregating or grouping data points by time.

Grafana automatically calculates an appropriate interval and it can be used as a variable in templated queries. The variable is either in seconds: $__interval or in milliseconds: $__interval_ms. It is typically used in aggregation functions like sum or average. For example, a Prometheus query using the interval variable: rate(http_requests_total[$__interval]).

This automatic interval is calculated based on the width of the graph. If the user zooms out a lot then the interval becomes greater, resulting in a more coarse grained aggregation whereas if the user zooms in then the interval decreases resulting in a more fine grained aggregation.

The part about deciding the Interval based on how wide the graph is confused me. If we are deciding the Interval based on graph width, then does that mean my graph width dictates how many data points I want to show? I’m confused about Interval’s relationship with query step. Do they affect each other?

I read about query step and resolution in these two links.

Please correct me if I have any misunderstandings.