optimize cache GC by stopping early

packages/backend/src/misc/cache.ts

@@ -200,7 +200,7 @@ export class RedisSingleCache<T> {
 
 export class MemoryKVCache<T> {
 	private readonly cache = new Map<string, { date: number; value: T; }>();
-	private readonly gcIntervalHandle = setInterval(() => this.gc(), 1000 * 60 * 3);
+	private readonly gcIntervalHandle = setInterval(() => this.gc(), 1000 * 60 * 3); // 3m
 
 	constructor(
 		private readonly lifetime: number,
@@ -289,12 +289,16 @@ export class MemoryKVCache<T> {
 	@bindThis
 	public gc(): void {
 		const now = Date.now();
+
 		for (const [key, { date }] of this.cache.entries()) {
-			if ((now - date) > this.lifetime) {
+			// The map is ordered from oldest to youngest.
+			// We can stop once we find an entry that's still active, because all following entries must *also* be active.
+			const age = now - date;
+			if (age < this.lifetime) break;
+
 			this.cache.delete(key);
 		}
 	}
-	}
 
 	@bindThis
 	public dispose(): void {