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Resurrect changes by shappir to improve memory usage of sparse histograms. #760

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Resurrect changes by shappir to improve memory usage of sparse histograms. #760

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e9ee891
perf: significantly improve the memory usage of histogram
Feb 6, 2024
21d9d0d
perf: use optional chaining
Feb 12, 2024
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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@zbjornson zbjornson Aug 9, 2026

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Not sure if you always use the "create merge commit" merge method, but the second commit is basically empty/has the wrong commit message and could be rebased out.

Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,8 @@ This release marks our first release under the Prometheus umbrella.
- chore: Add copyright license headers and test
- Make cluster and worker-thread metric aggregation order deterministic
- Export `MetricObject`, `MetricObjectWithValues`, `MetricValue` and `MetricValueWithName` from the TypeScript definitions
- perf: Improve the memory usage of histograms by delaying allocation of bucket data
- fix: Avoid updating exemplar values during subsequent metric changes (Fixes [#616](https://github.com/prometheus/client_js/issues/616))

### Added

Expand Down
56 changes: 25 additions & 31 deletions lib/histogram.js
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,7 @@ class Histogram extends Metric {
this.type = 'histogram';
this.defaultLabels = {};
this.defaultExemplarLabelSet = {};
this.enableExemplars = false;
this.enableExemplars = config.enableExemplars;

for (const label of this.labelNames) {
if (label === 'le') {
Expand All @@ -51,26 +51,17 @@ class Histogram extends Metric {
return acc;
}, {});

if (config.enableExemplars) {
this.enableExemplars = true;
this.bucketExemplars = this.upperBounds.reduce((acc, upperBound) => {
acc[upperBound] = null;
return acc;
}, {});
Object.freeze(this.bucketExemplars);
this.observe = this.observeWithExemplar;
} else {
this.observe = this.observeWithoutExemplar;
}
this.observe = this.enableExemplars
? this.observeWithExemplar
: this.observeWithoutExemplar;

Object.freeze(this.bucketValues);
Object.freeze(this.upperBounds);

if (this.labelNames.length === 0) {
this.store = new LabelMap(this.labelNames);
this.store.merge(
{},
createBaseValues({}, this.bucketValues, this.bucketExemplars),
createBaseValues({}, this.bucketValues, this.enableExemplars),
);
}
}
Expand All @@ -90,14 +81,13 @@ class Histogram extends Metric {
value,
exemplarLabels = this.defaultExemplarLabelSet,
} = {}) {
observe(this, labels === 0 ? 0 : labels || {}, value);
this.updateExemplar(labels, value, exemplarLabels);
const valueFromMap = observe(this, labels === 0 ? 0 : labels || {}, value);
this.updateExemplar(valueFromMap, value, exemplarLabels);
}

updateExemplar(labels, value, exemplarLabels) {
updateExemplar({ bucketExemplars }, value, exemplarLabels) {
if (isEmpty(exemplarLabels)) return;
const bound = findBound(this.upperBounds, value);
const { bucketExemplars } = this.store.entry(labels);
let exemplar = bucketExemplars[bound];
if (!isObject(exemplar)) {
exemplar = new Exemplar();
Expand Down Expand Up @@ -147,7 +137,7 @@ class Histogram extends Metric {
this.store.validate(labels);
this.store.merge(
labels,
createBaseValues(labels, this.bucketValues, this.bucketExemplars),
createBaseValues(labels, this.bucketValues, this.enableExemplars),
);
}

Expand All @@ -173,7 +163,9 @@ class Histogram extends Metric {
const labels = getLabels(this.labelNames, args);
this.store.validate(labels);
return {
observe: value => observe(this, labels, value),
observe: value => {
observe(this, labels, value);
},
startTimer: () => startTimer(this, labels),
};
}
Expand Down Expand Up @@ -233,6 +225,7 @@ function findBound(upperBounds, value) {
* @param {Histogram} histogram
* @param {object} labels - Object with labels where key is the label key and value is label value. Can only be one level deep
* @param {number} value - Value to observe in the histogram
* @returns {object} bucket data
*/
function observe(histogram, labels, value) {
const labelValuePair = convertLabelsAndValues(labels, value);
Expand All @@ -251,7 +244,7 @@ function observe(histogram, labels, value) {
createBaseValues(
labelValuePair.labels,
histogram.bucketValues,
histogram.bucketExemplars,
histogram.enableExemplars,
),
);
}
Expand All @@ -261,20 +254,22 @@ function observe(histogram, labels, value) {
entry.sum += labelValuePair.value;
entry.count += 1;

if (Object.hasOwn(entry.bucketValues, b)) {
if (typeof entry.bucketValues[b] === 'number') {
entry.bucketValues[b] += 1;
}

return entry;
}

function createBaseValues(labels, bucketValues, bucketExemplars) {
function createBaseValues(labels, bucketValues, enableExemplars) {
const result = {
labels,
bucketValues: { ...bucketValues },
bucketValues: Object.create(bucketValues),
sum: 0,
count: 0,
};
if (bucketExemplars) {
result.bucketExemplars = { ...bucketExemplars };
if (enableExemplars) {
result.bucketExemplars = {};
}
return result;
}
Expand All @@ -295,16 +290,15 @@ function extractBucketValuesForExport(histogram) {
const name = `${histogram.name}_bucket`;
return bucketData => {
let acc = 0;
const { labels, bucketValues, bucketExemplars } = bucketData;
const buckets = histogram.upperBounds.map(upperBound => {
acc += bucketData.bucketValues[upperBound];
acc += bucketValues[upperBound];
return setValuePair(
{ le: upperBound },
acc,
name,
bucketData.bucketExemplars
? bucketData.bucketExemplars[upperBound]
: null,
bucketData.labels,
bucketExemplars?.[upperBound] ?? null,
labels,
);
});
return { buckets, data: bucketData };
Expand Down
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