Use s-curve backoff when refreshing github checks

app/src/lib/backoff/scurve.test.ts

@@ -0,0 +1,24 @@
+import { scurveBackoff } from './scurve';
+import { expect, test } from 'vitest';
+
+test('test s-curve backoff 1', () => {
+	const min = 1000;
+	const max = 20000;
+	const initialDelay = scurveBackoff(0, min, max);
+	expect(initialDelay).toBeGreaterThan(min);
+	expect(initialDelay).toBeLessThan(1.1 * min);
+
+	const finalDelay = scurveBackoff(Number.MAX_SAFE_INTEGER, min, max);
+	expect(finalDelay).toEqual(max);
+});
+
+test('test s-curve backoff 2', () => {
+	const min = 10000;
+	const max = 600000;
+	const initialDelay = scurveBackoff(0, min, max);
+	expect(initialDelay).toBeGreaterThan(min);
+	expect(initialDelay).toBeLessThan(1.1 * min);
+
+	const finalDelay = scurveBackoff(Number.MAX_SAFE_INTEGER, min, max);
+	expect(finalDelay).toEqual(max);
+});

app/src/lib/backoff/scurve.ts

@@ -0,0 +1,6 @@
+export function scurveBackoff(ageMs: number, min: number, max: number): number {
+	// S-curve (sigmoid) with y-axis intercept is at ~10 seconds and max value at 10 minutes.
+	const delaySeconds =
+		(max - min) / 1000 / (1 + Math.exp(-(ageMs / 1000 - 2000) / 300)) + min / 1000;
+	return delaySeconds * 1000;
+}

app/src/lib/gitHost/github/githubChecksMonitor.ts

@@ -1,3 +1,4 @@
+import { scurveBackoff } from '$lib/backoff/scurve';
 import { DEFAULT_HEADERS } from '$lib/gitHost/github/headers';
 import { parseGitHubCheckSuites } from '$lib/gitHost/github/types';
 import { sleep } from '$lib/utils/sleep';
@@ -78,9 +79,7 @@ export class GitHubChecksMonitor implements GitHostChecksMonitor {
 		// to a branch GitHub might not report all the checks that will eventually be
 		// run as part of the suite.
 		if (status.completed && ageMs > MIN_COMPLETED_AGE) return;
-
-		const backoff = getBackoffByAge(ageMs);
-		return backoff;
+		return scurveBackoff(ageMs, 10000, 600000);
 	}
 
 	private async fetchChecksWithRetries(ref: string, retries: number, delayMs: number) {
@@ -170,16 +169,3 @@ function parseChecks(
 		finished
 	};
 }
-
-export function getBackoffByAge(age: number) {
-	if (age < 60000) {
-		return 10000;
-	} else if (age < 600000) {
-		return 30000;
-	} else if (age < 1200000) {
-		return 60000;
-	} else if (age < 3600000) {
-		return 120000;
-	}
-	return;
-}