Federation endpoint does not comply with the exposition format specification

[beorn7]

Currently, the federation endpoint exposes one MetricFamily for each time series, thus duplicating a lot of information.

While Prometheus ingests such duplicated MetricFamilies just fine in protobuf format, the text format spec is less lenient about the duplication. Since the text format creator in the expfmt package faithfully translates the duplicated MetricFamilies, the text format output is currently not valid.

We might make it valid, see prometheus/common#54 , but we should also investigate the cost/benefit ratio for collapsing the MetricFamily in federation (saves network bandwidth and the cost of (de-)compression and decoding).

[beorn7]

I had another look at the spec. The protobuf spec is actually as strict as the text format spec WRT repeated metric names: "Each MetricFamily within the same exposition must have a unique name."

So it's a bug even on the protobuf level.

[lock]

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