From 152a024c6e7d3dd0ba862ff16d060f0be99e37ff Mon Sep 17 00:00:00 2001
From: Chengzhong Wu <chengzhong.wcz@alibaba-inc.com>
Date: Fri, 13 Jan 2023 17:13:11 +0800
Subject: [PATCH] feat(sdk-metrics): apply binary search in histogram

---
 .../sdk-metrics/src/aggregator/Histogram.ts   | 12 ++-----
 packages/sdk-metrics/src/utils.ts             | 27 ++++++++++++++++
 packages/sdk-metrics/test/utils.test.ts       | 31 ++++++++++++++++++-
 3 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/packages/sdk-metrics/src/aggregator/Histogram.ts b/packages/sdk-metrics/src/aggregator/Histogram.ts
index a916e182484..e7b81891eb1 100644
--- a/packages/sdk-metrics/src/aggregator/Histogram.ts
+++ b/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 {
diff --git a/packages/sdk-metrics/src/utils.ts b/packages/sdk-metrics/src/utils.ts
index c2bc4408495..835de92fe1b 100644
--- a/packages/sdk-metrics/src/utils.ts
+++ b/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;
+}
diff --git a/packages/sdk-metrics/test/utils.test.ts b/packages/sdk-metrics/test/utils.test.ts
index 04633a14ba6..16ec0a2b3a0 100644
--- a/packages/sdk-metrics/test/utils.test.ts
+++ b/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]);
+      });
+    }
+  });
 });