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METRICS.md

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Snap Metrics

A metric in snap has the following fields.

  • Namespace []core.NamespaceElement
  • Uniquely identifies the metric
  • LastAdvertisedTime time.Time
  • Describes when the metric was added to the metric catalog
  • Version int
  • Is bound to the version of the plugin
  • Multiple versions of the same metric can be added to the catalog
  • Unless specified in the Task Manifest, the latest available metric will collected
  • Config *cdata.ConfigDataNode
  • Contains data needed to collect a metric
  • Examples include 'uri', 'username', 'password', 'paths'
  • Data interface{}
  • The collected data
  • Tags map[string]string
  • Are key value pairs that provide additional meta data about the metric
  • May be added by the framework or other plugins (processors)
  • The framework currently adds the following standard tag to all metrics
  • plugin_running_on describing on which host the plugin is running. This value is updated every hour due to a TTL set internally.
  • May be added by a task manifests as described here
  • May be added by the snapd config as described here
  • Unit string
  • Describes the magnititude being measured
  • Can be an empty string for unitless data
  • See Metrics20.org for more guidance on units
  • Description string
  • Is stored in the metric catalog and meant to give the user more details about the metric such as how it is derived
  • Timestamp time.Time
  • Describes when the metric was collected

Static Metrics

A metric is described as static when the string representation of the namespace has no wildcards.

String representation examples:

/intel/cassandra/node/zeus/type/Cache/scope/KeyCache/name/Requests/OneMinuteRate
/intel/cassandra/node/zeus/type/ClientRequest/scope/CASRead/name/Unavailables/FiveMinuteRate
/intel/cassandra/node/apollo/type/Cache/scope/RowCache/name/Hits/OneMinuteRate
/intel/cassandra/node/apollo/type/ClientRequest/scope/RangeSlice/name/Latency/OneMinuteRate

Dynamic Metrics

A metric is described as dynamic when it includes one or more wildcards.

String representation examples:

/intel/cassandra/node/*/type/*/scope/*/name/*/OneMinuteRate
/intel/cassandra/node/*/type/*/scope/*/name/*/FiveMinuteRate
/intel/cassandra/node/*/type/*/keyspace/*/name/*/OneMinuteRate
/intel/cassandra/node/*/type/*/keyspace/*/name/*/FiveMinuteRate

Metric Namespace

As described above a metrics Namespace is an array of NamespaceElements ([]core.NamespaceElement).

A NamespaceElement has the following fields.

  • Value string
  • Description string
  • Only used to describe dynamic components of a namespace
  • Name string
  • Only used to describe dynamic components of a namespace

Static Metric Namespace Example

Given a static metric identified by the namespace /intel/psutil/load/load1 the NamespaceElements would have values of 'intel', 'psutil', 'load' and "load1" respectively. The Name and Description fields would have empty values.

The metric's namespace could be created using the following constructor function.

namespace := core.NewNamespace("intel", "psutil", "load", "load1")

Dynamic Metric Namespace Example

Dynamic namespaces enable collector plugins to embed runtime data in the namespace with just enough metadata to enable downstrean plugins (processors and publishers) the ability to extract the data and transform the namespace into its canonical form often required by some backends.

Given a dynamic metric identified by the namespace /intel/libvirt/*/disk/*/wrreq the NamespaceElements would have values of 'intel', 'libvirt', '', 'disk', '' and 'wrreq' respectively. The Name and Description fields of the 2nd and 4th elements would also contain non empty values.

The metric's namespace could be created using the following constructor function.

ns := core.NewNamespace("intel", "libvirt")
    .AddDynamicElement("domain_name", "Domain Name")
    .AddStaticElement("disk")
    .AddDynamicElement("disk_name", "Disk Name")
    .AddStaticElement("wrreq")

It is important to note that the NamespaceElement fields Name and Description should only have non-empty string values when the element they are describing is dynamic in which case the Value field would contain the string value "*".

You can find an example of the influxdb publisher creating tags out of the dynamic elements of the namespace and publishing to a time series here. Using the example above we can expect a datapoint published to a time series with the name /intel/libvirt/disk/wrreq with tags describing domain_name and disk_name.