# `Prometheus.Metric.Summary`
[🔗](https://github.com/prometheus-erl/prometheus.ex/blob/v5.1.0/lib/prometheus/metric/summary.ex#L1)

Summary metric, to track the size of events.

Example use cases for Summaries:
  - Response latency;
  - Request size;
  - Response size.

Example:

```
defmodule MyProxyInstrumenter do

  use Prometheus.Metric

  ## to be called at app/supervisor startup.
  ## to tolerate restarts use declare.
  def setup() do
    Summary.declare([name: :request_size_bytes,
                     help: "Request size in bytes."])

    Summary.declare([name: :response_size_bytes,
                     help: "Response size in bytes."])
  end

  def observe_request(size) do
    Summary.observe([name: :request_size_bytes], size)
  end

  def observe_response(size) do
    Summary.observe([name: :response_size_bytes], size)
  end
end
```

# `declare`

Creates a summary using `spec`.
Summary cannot have a label named "quantile".

If a summary with the same `spec` exists returns `false`.

Raises `Prometheus.MissingMetricSpecKeyError` if required `spec` key is missing.<br>
Raises `Prometheus.InvalidMetricNameError` if metric name is invalid.<br>
Raises `Prometheus.InvalidMetricHelpError` if help is invalid.<br>
Raises `Prometheus.InvalidMetricLabelsError` if labels isn't a list.<br>
Raises `Prometheus.InvalidMetricNameError` if label name is invalid;<br>
Raises `Prometheus.InvalidValueError` exception if duration_unit is unknown or
doesn't match metric name.

# `new`

Creates a summary using `spec`.
Summary cannot have a label named "quantile".

Raises `Prometheus.MissingMetricSpecKeyError` if required `spec` key is missing.<br>
Raises `Prometheus.InvalidMetricNameError` if metric name is invalid.<br>
Raises `Prometheus.InvalidMetricHelpError` if help is invalid.<br>
Raises `Prometheus.InvalidMetricLabelsError` if labels isn't a list.<br>
Raises `Prometheus.InvalidMetricNameError` if label name is invalid.<br>
Raises `Prometheus.InvalidValueError` exception if duration_unit is unknown or
doesn't match metric name.<br>
Raises `Prometheus.MFAlreadyExistsError` if a summary with the same `spec`
already exists.

# `observe`

Observes the given amount.

Raises `Prometheus.InvalidValueError` exception if `amount` isn't a number.<br>
Raises `Prometheus.UnknownMetricError` exception if a summary for `spec`
can't be found.<br>
Raises `Prometheus.InvalidMetricArityError` exception if labels count mismatch.

# `observe_duration`
*macro* 

Observes the amount of time spent executing `body`.

Raises `Prometheus.UnknownMetricError` exception if a summary for `spec`
can't be found.<br>
Raises `Prometheus.InvalidMetricArityError` exception if labels count mismatch.
Raises `Prometheus.InvalidValueError` exception if `fun` isn't a function or block.

# `remove`

Removes summary series identified by spec.

Raises `Prometheus.UnknownMetricError` exception if a summary for `spec`
can't be found.<br>
Raises `Prometheus.InvalidMetricArityError` exception if labels count mismatch.

# `reset`

Resets the value of the summary identified by `spec`.

Raises `Prometheus.UnknownMetricError` exception if a summary for `spec`
can't be found.<br>
Raises `Prometheus.InvalidMetricArityError` exception if labels count mismatch.

# `value`

Returns the value of the summary identified by `spec`. If there is no summary for
given labels combination, returns `:undefined`.

If duration unit set, sum will be converted to the duration unit.
[Read more here.](time.html)

Raises `Prometheus.UnknownMetricError` exception if a summary for `spec`
can't be found.<br>
Raises `Prometheus.InvalidMetricArityError` exception if labels count mismatch.

---

*Consult [api-reference.md](api-reference.md) for complete listing*