doc/prometheus: Mention the long running avg types

Signed-off-by: Boris Ranto <branto@redhat.com>
(cherry picked from commit 7f468f4d51a23d61063f28c46b5e247c5a309762)

diff --git a/doc/mgr/prometheus.rst b/doc/mgr/prometheus.rst
index eb869d11872b526ff650617b69d46cb805fa0d37..fc2f15fe235d4f6cbccf72d71eb747328945cd42 100644 (file)
--- a/doc/mgr/prometheus.rst
+++ b/doc/mgr/prometheus.rst
@@ -49,6 +49,12 @@ The *cluster* statistics (i.e. those global to the Ceph cluster)
 have labels appropriate to what they report on.  For example, 
 metrics relating to pools have a ``pool_id`` label.
 
+
+The long running averages that represent the histograms from core Ceph
+are represented by a pair of ``<name>_sum`` and ``<name>_count`` metrics.
+This is similar to how histograms are represented in `Prometheus <https://prometheus.io/docs/concepts/metric_types/#histogram>`_
+and they can also be treated `similarly <https://prometheus.io/docs/practices/histograms/>`_.
+
 Pool and OSD metadata series
 ----------------------------