# Custom Distribution

Custom distributions are used to record the distribution of arbitrary values.

It should be used only when direct control over how the histogram buckets are computed is required. Otherwise, look at the standard distribution metric types:

Note: Custom distributions are currently not universally supported. See below for available APIs.

## Recording API

### accumulateSamples

Accumulate the provided samples in the metric.

import org.mozilla.yourApplication.GleanMetrics.Graphics

Graphics.checkerboardPeak.accumulateSamples([23])

import org.mozilla.yourApplication.GleanMetrics.Graphics;

Graphics.INSTANCE.checkerboardPeak().accumulateSamples(listOf(23));

Graphics.checkerboardPeak.accumulateSamples([23])

from glean import load_metrics

metrics.graphics.checkerboard_peak.accumulate_samples([23])

use glean_metrics::graphics;

graphics::checkerboard_peak.accumulate_samples_signed(vec![23]);

import * as graphics from "./path/to/generated/files/graphics.js";

graphics.checkerboardPeak.accumulateSamples([23]);


C++

#include "mozilla/glean/GleanMetrics.h"

mozilla::glean::graphics::checkerboard_peak.AccumulateSamples({ 23 });


JavaScript

Glean.graphics.checkerboardPeak.accumulateSamples([23])


#### Limits

• The maximum value of bucket_count is 100.
• Only non-negative values may be recorded (>= 0).

#### Recorded errors

• invalid_value: If recording a negative value.

## Testing API

### testGetValue

Gets the recorded value for a given counter metric.
Returns a struct with counts per buckets and total sum if data is stored.
Returns a language-specific empty/null value if no data is stored.

import org.mozilla.yourApplication.GleanMetrics.Graphics

// Get snapshot
val snapshot = Graphics.checkerboardPeak.testGetValue()

// Does the sum have the expected value?
assertEquals(23, snapshot.sum)

// Does the count have the expected value?
assertEquals(1L, snapshot.count)

// Buckets are indexed by their lower bound.
assertEquals(1L, snapshot.values[19])

import org.mozilla.yourApplication.GleanMetrics.Graphics;

// Get snapshot
val snapshot = Graphics.INSTANCE.checkerboardPeak().testGetValue();

// Does the sum have the expected value?
assertEquals(23, snapshot.sum);

// Does the count have the expected value?
assertEquals(1L, snapshot.count);

// Get snapshot.
let snapshot = graphics.checkerboardPeak.testGetValue()

// Does the sum have the expected value?
XCTAssertEqual(23, snapshot.sum)

// Does the count have the expected value?
XCTAssertEqual(1, snapshot.count)

// Buckets are indexed by their lower bound.
XCTAssertEqual(1L, snapshot.values[19])

from glean import load_metrics

# Get snapshot.
snapshot = metrics.graphics.checkerboard_peak.test_get_value()

# Does the sum have the expected value?
assert 23 == snapshot.sum

# Does the count have the expected value?
assert 1 == snapshot.count

# Buckets are indexed by their lower bound.
assert 1 == snapshot.values[19]

use glean_metrics::graphics;

// Does the sum have the expected value?
assert_eq!(23, graphics::checkerboard_peak.test_get_value(None).unwrap().sum);

// Does the count have the expected value?
assert_eq!(1, graphics::checkerboard_peak.test_get_value(None).unwrap().count);

// Buckets are indexed by their lower bound.
assert_eq!(1, snapshot.values[19])

import * as graphics from "./path/to/generated/files/graphics.js";

// Get snapshot
const snapshot = await graphics.checkerboardPeak.testGetValue();

// Does the sum have the expected value?
assert.equal(23, snapshot.sum);

// Buckets are indexed by their lower bound.
assert.equal(1, snapshot.values[19]);


C++

#include "mozilla/glean/GleanMetrics.h"

auto data = mozilla::glean::graphics::checkerboard_peak.TestGetValue().value();
ASSERT_EQ(23UL, data.sum);


JavaScript

let data = Glean.graphics.checkerboardPeak.testGetValue();
Assert.equal(23, data.sum);


### testGetNumRecordedErrors

Gets the number of errors recorded for a the custom distribution metric.

import org.mozilla.yourApplication.GleanMetrics.Graphics

/// Did the metric receive a negative value?
assertEquals(
0,
Graphics.checkerboardPeak.testGetNumRecordedErrors(ErrorType.INVALID_VALUE)
)

import org.mozilla.yourApplication.GleanMetrics.Graphics;

/// Did the metric receive a negative value?
assertEquals(
0,
Graphics.INSTANCE.checkerboardPeak().testGetNumRecordedErrors(
ErrorType.INVALID_VALUE
)
)

// Assert that no errors were recorded.
XCTAssertEqual(0, Graphics.checkerboardPeak.testGetNumRecordedErrors(.invalidValue))

from glean import load_metrics

# Assert that no errors were recorded.
assert 0 == metrics.graphics.checkerboard_peak.test_get_num_recorded_errors(
ErrorType.INVALID_VALUE
)

use glean::ErrorType;
use glean_metrics::graphics;

// Were any of the values negative and thus caused an error to be recorded?
assert_eq!(
0,
graphics::checkerboard_peak.test_get_num_recorded_errors(
ErrorType::InvalidValue,
None
)
);

import * as graphics from "./path/to/generated/files/graphics.js";
import { ErrorType } from "@mozilla/glean/<platform>";

// Did the metric receive a negative value?
assert.equal(
0,
graphics.checkerboardPeak.testGetNumRecordedErrors(ErrorType.InvalidValue)
);


## Metric Parameters

Example custom distribution metric definition:

graphics:
checkerboard_peak:
type: custom_distribution
description: >
Peak number of CSS pixels checkerboarded during a checkerboard event.
range_min: 1
range_max: 66355200
bucket_count: 50
histogram_type: exponential
unit: pixels
gecko_datapoint: CHECKERBOARD_PEAK
bugs:
- https://bugzilla.mozilla.org/000000
data_reviews:
- https://bugzilla.mozilla.org/show_bug.cgi?id=000000#c3
- me@mozilla.com
expires: 2020-10-01


### Extra metric parameters

Custom distributions have the following required parameters:

• range_min: (Integer) The minimum value of the first bucket
• range_max: (Integer) The minimum value of the last bucket
• bucket_count: (Integer) The number of buckets
• histogram_type:
• linear: The buckets are evenly spaced
• exponential: The buckets follow a natural logarithmic distribution

Note Check out how these bucketing algorithms would behave on the Custom distribution simulator.

Custom distributions have the following optional parameters:

• unit: (String) The unit of the values in the metric. For documentation purposes only -- does not affect data collection.
• gecko_datapoint: (String) This is a Gecko-specific property. It is the name of the Gecko metric to accumulate the data from, when using a Glean SDK in a product using GeckoView.