feat(sdk-metrics): apply binary search in histogram

CHANGELOG.md

@@ -11,6 +11,8 @@ For experimental package changes, see the [experimental CHANGELOG](experimental/
 
 ### :rocket: (Enhancement)
 
+- feat(sdk-metrics): apply binary search in histogram recording [#3539](https://github.com/open-telemetry/opentelemetry-js/pull/3539) @legendecas
+
 ### :bug: (Bug Fix)
 
 ### :books: (Refine Doc)

packages/sdk-metrics/src/aggregator/Histogram.ts

@@ -23,7 +23,7 @@ import {
 import { DataPointType, HistogramMetricData } from '../export/MetricData';
 import { HrTime } from '@opentelemetry/api';
 import { InstrumentDescriptor, InstrumentType } from '../InstrumentDescriptor';
-import { Maybe } from '../utils';
+import { binarySearchLB, Maybe } from '../utils';
 import { AggregationTemporality } from '../export/AggregationTemporality';
 
 /**
@@ -77,14 +77,8 @@ export class HistogramAccumulation implements Accumulation {
       this._current.hasMinMax = true;
     }
 
-    for (let i = 0; i < this._boundaries.length; i++) {
-      if (value < this._boundaries[i]) {
-        this._current.buckets.counts[i] += 1;
-        return;
-      }
-    }
-    // value is above all observed boundaries
-    this._current.buckets.counts[this._boundaries.length] += 1;
+    const idx = binarySearchLB(this._boundaries, value);
+    this._current.buckets.counts[idx + 1] += 1;
   }
 
   setStartTime(startTime: HrTime): void {
@@ -104,7 +98,7 @@ export class HistogramAggregator implements Aggregator<HistogramAccumulation> {
   public kind: AggregatorKind.HISTOGRAM = AggregatorKind.HISTOGRAM;
 
   /**
-   * @param _boundaries upper bounds of recorded values.
+   * @param _boundaries sorted upper bounds of recorded values.
    * @param _recordMinMax If set to true, min and max will be recorded. Otherwise, min and max will not be recorded.
    */
   constructor(

packages/sdk-metrics/src/utils.ts

@@ -163,3 +163,30 @@ export function setEquals(lhs: Set<unknown>, rhs: Set<unknown>): boolean {
   }
   return true;
 }
+
+/**
+ * Binary search the sorted array to the find lower bound for the value.
+ * @param arr
+ * @param value
+ * @returns
+ */
+export function binarySearchLB(arr: number[], value: number): number {
+  let lo = 0;
+  let hi = arr.length - 1;
+
+  while (hi - lo > 1) {
+    const mid = Math.trunc((hi + lo) / 2);
+    if (arr[mid] <= value) {
+      lo = mid;
+    } else {
+      hi = mid - 1;
+    }
+  }
+
+  if (arr[hi] <= value) {
+    return hi;
+  } else if (arr[lo] <= value) {
+    return lo;
+  }
+  return -1;
+}

packages/sdk-metrics/test/utils.test.ts

@@ -16,7 +16,12 @@
 
 import * as sinon from 'sinon';
 import * as assert from 'assert';
-import { callWithTimeout, hashAttributes, TimeoutError } from '../src/utils';
+import {
+  binarySearchLB,
+  callWithTimeout,
+  hashAttributes,
+  TimeoutError,
+} from '../src/utils';
 import { assertRejects } from './test-utils';
 import { MetricAttributes } from '@opentelemetry/api';
 
@@ -60,4 +65,28 @@ describe('utils', () => {
       }
     });
   });
+
+  describe('binarySearchLB', () => {
+    const tests = [
+      /** [ arr, value, expected lb idx ] */
+      [[0, 10, 100, 1000], -1, -1],
+      [[0, 10, 100, 1000], 0, 0],
+      [[0, 10, 100, 1000], 1, 0],
+      [[0, 10, 100, 1000], 10, 1],
+      [[0, 10, 100, 1000], 1000, 3],
+      [[0, 10, 100, 1000], 1001, 3],
+
+      [[0, 10, 100, 1000, 10_000], -1, -1],
+      [[0, 10, 100, 1000, 10_000], 0, 0],
+      [[0, 10, 100, 1000, 10_000], 10, 1],
+      [[0, 10, 100, 1000, 10_000], 1001, 3],
+      [[0, 10, 100, 1000, 10_000], 10_001, 4],
+    ] as [number[], number, number][];
+
+    for (const [idx, test] of tests.entries()) {
+      it(`test idx(${idx}): find lb of ${test[1]} in [${test[0]}]`, () => {
+        assert.strictEqual(binarySearchLB(test[0], test[1]), test[2]);
+      });
+    }
+  });
 });