Cannot apply range selectors

[maur...@gmail.com]

Hi to all,
I've just discovered Prometheus so I'm testing it.

I've run the current master version with docker and executing the sample query "http_requests_total[5m]" (found on the documentation, see http://prometheus.io/docs/querying/basics/ chapter "Range Vector Selectors") the server returns the following response:

> Error executing query: invalid expression type "matrix" for range query, must be scalar or vector

Is it a bug or I'm mistaking something?

Thanks,
Mauro

[Julius Volz]

Hi,

An expression that returns a range vector can only be queried in tabular view, not in the graph view. The reason is that a graph query itself already evaluates an entire expression over time, so you'd be getting back a whole range of values at each every sampling point along the graph (which doesn't make sense to graph). What you *do* use range vectors for in graphs is things like rates or deltas that take a range vector and return an instant vector, like: rate(http_requests_total[5m]).

The short rule is that only expressions that return an instant vector can be graphed.

Cheers,

Julius

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[Mauro Rocchi]

Hi Julius,

many thanks for the clarification.

Mauro

[hero...@gmail.com]

This is something really confusing. It should be included in the doc. Thank you very much for clarifying that!