Metrics Semantic Conventions
The following semantic conventions surrounding metrics are defined:
- HTTP: For HTTP client and server metrics.
- System: For standard system metrics.
- Process: For standard process metrics.
- Runtime Environment: For runtime environment metrics.
- FaaS: For Function as a Service metrics.
Metric names and attributes exist within a single universe and a single hierarchy. Metric names and attributes MUST be considered within the universe of all existing metric names. When defining new metric names and attributes, consider the prior art of existing standard metrics and metrics from frameworks/libraries.
Associated metrics SHOULD be nested together in a hierarchy based on their usage. Define a top-level hierarchy for common metric categories: for OS metrics, like CPU and network; for app runtimes, like GC internals. Libraries and frameworks should nest their metrics into a hierarchy as well. This aids in discovery and adhoc comparison. This allows a user to find similar metrics given a certain metric.
The hierarchical structure of metrics defines the namespacing. Supporting OpenTelemetry artifacts define the metric structures and hierarchies for some categories of metrics, and these can assist decisions when creating future metrics.
Common attributes SHOULD be consistently named. This aids in discoverability and disambiguates similar attributes to metric names.
“As a rule of thumb, aggregations over all the attributes of a given metric SHOULD be meaningful,” as Prometheus recommends.
Semantic ambiguity SHOULD be avoided. Use prefixed metric names in cases
where similar metrics have significantly different implementations across the
breadth of all existing metrics. For example, every garbage collected runtime
has slightly different strategies and measures. Using a single set of metric
names for GC, not divided by the runtime, could create dissimilar comparisons
and confusion for end users. (For example, prefer
process.runtime.gc.*.) Measures of many operating system metrics are similarly
Name Reuse Prohibition
A new metric MUST NOT be added with the same name as a metric that existed in the past but was renamed (with a corresponding schema file).
When introducing a new metric name check all existing schema files to make sure the name does not appear as a key of any “rename_metrics” section (keys denote old metric names in rename operations).
Conventional metrics or metrics that have their units included in
OpenTelemetry metadata (e.g.
metric.WithUnit in Go) SHOULD NOT include the
units in the metric name. Units may be included when it provides additional
meaning to the metric name. Metrics MUST, above all, be understandable and
When building components that interoperate between OpenTelemetry and a system using the OpenMetrics exposition format, use the OpenMetrics Guidelines.
Metric names SHOULD NOT be pluralized, unless the value being recorded
represents discrete instances of a
Generally, the name SHOULD be pluralized only if the unit of the metric in
question is a non-unit (like
system.cpu.timeshould not be pluralized, even if many data points are recorded.
system.network.packetsshould be pluralized, even if only a single data point is recorded.
General Metric Semantic Conventions
The following semantic conventions aim to keep naming consistent. They provide guidelines for most of the cases in this specification and should be followed for other instruments not explicitly defined in this document.
limit - an instrument that measures the constant, known total amount of something should be called
entity.limit. For example,
system.memory.limitfor the total amount of memory on a system.
usage - an instrument that measures an amount used out of a known total (limit) amount should be called
entity.usage. For example,
state = used | cached | free | ...for the amount of memory in a each state. Where appropriate, the sum of usage over all attribute values SHOULD be equal to the limit.
A measure of the amount consumed of an unlimited resource, or of a resource whose limit is unknowable, is differentiated from usage. For example, the maximum possible amount of virtual memory that a process may consume may fluctuate over time and is not typically known.
utilization - an instrument that measures the fraction of usage out of its limit should be called
entity.utilization. For example,
system.memory.utilizationfor the fraction of memory in use. Utilization values are in the range
time - an instrument that measures passage of time should be called
entity.time. For example,
state = idle | user | system | .... time measurements are not necessarily wall time and can be less than or greater than the real wall time between measurements.
time instruments are a special case of usage metrics, where the limit can usually be calculated as the sum of time over all attribute values. utilization for time instruments can be derived automatically using metric event timestamps. For example,
system.cpu.utilizationis defined as the difference in
system.cpu.timemeasurements divided by the elapsed time and number of CPUs.
io - an instrument that measures bidirectional data flow should be called
entity.ioand have attributes for direction. For example,
Other instruments that do not fit the above descriptions may be named more freely. For example,
system.network.packets. Units do not need to be specified in the names since they are included during instrument creation, but can be added if there is ambiguity.
- Instruments for utilization metrics (that measure the fraction out of a
total) are dimensionless and SHOULD use the default unit
- Instruments that measure an integer count of something SHOULD only use
annotations with curly braces to
give additional meaning without the leading default unit (
1). For example, use