add p90ms measurement

Author: dario-piotrowicz

benchmarking/src/benchmarking.ts

@@ -1,10 +1,12 @@
 import nodeTimesPromises from "node:timers/promises";
 import nodeFsPromises from "node:fs/promises";
 import nodePath from "node:path";
+import { getPercentile } from "./utils";
 
 export type FetchBenchmark = {
   callDurationsMs: number[];
   averageMs: number;
+  p90Ms: number;
 };
 
 export type BenchmarkingResults = {
@@ -82,9 +84,12 @@ async function benchmarkFetch(url: string, options: BenchmarkFetchOptions): Prom
 
   const averageMs = callDurationsMs.reduce((time, sum) => sum + time) / callDurationsMs.length;
 
+  const p90Ms = getPercentile(callDurationsMs, 90);
+
   return {
     callDurationsMs,
     averageMs,
+    p90Ms,
   };
 }
 

benchmarking/src/index.ts

@@ -33,6 +33,7 @@ console.log("\n\nSummary: ");
 const summary = benchmarkingResults.map(({ name, fetchBenchmark }) => ({
   name,
   "average fetch duration (ms)": Math.round(fetchBenchmark.averageMs),
+  "90th percentile (ms)": Math.round(fetchBenchmark.p90Ms),
 }));
 console.table(summary);
 

benchmarking/src/utils.ts

@@ -37,3 +37,25 @@ export async function parallelRunWithSpinner<T>(
 
   return results;
 }
+
+/**
+ * Gets a specific percentile for a given set of numbers
+ *
+ * @param data the data which percentile value needs to be computed
+ * @param percentile the requested percentile (a number between 0 and 100)
+ * @returns the computed percentile
+ */
+export function getPercentile(data: number[], percentile: number): number {
+  if (Number.isNaN(percentile) || percentile < 0 || percentile > 100) {
+    throw new Error(`A percentile needs to be between 0 and 100, found: ${percentile}`);
+  }
+
+  data = data.sort((a, b) => a - b);
+
+  const rank = (percentile / 100) * (data.length - 1);
+
+  const rankInt = Math.floor(rank);
+  const rankFract = rank - rankInt;
+
+  return Math.round(data[rankInt]! + rankFract * (data[rankInt + 1]! - data[rankInt]!));
+}