[SOLR-12564] Full support for histogram and summary metric types in Prometheus exporter

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 7.3.1
• Component/s: contrib - prometheus-exporter, metrics
• Assignee: Unassigned
• Reporter: Michał Politowski
• Created: 19/Jul/18 15:24
• Updated: 29/Nov/20 06:23

Description

The Prometheus metrics exporter in contrib does not support exposing complex metrics types: histograms and summaries. In particular request times metrics in Solr provide quantile values, which could be exposed as a Prometheus summary.

These complex types are represented in the Prometheus wire format as multiple samples with different, related names, which should be produced in a particular order under a common header as described in https://prometheus.io/docs/instrumenting/exposition_formats/

The current Solr Prometheus exporter is able to produce any required sample lines, but not to group them as specified.

This is only a minor issue for now, as Prometheus currently seems to ignore these constraints (and metrics types in general) itself, but this may change in the future (as stated eg. in https://prometheus.io/docs/concepts/metric_types/)