From ba093382682380ddf1bb756e9d83b31b776fa7af Mon Sep 17 00:00:00 2001
From: Hazel K <acomputerdog@gmail.com>
Date: Sun, 4 Aug 2024 09:58:01 -0400
Subject: [PATCH] optimize cache GC by stopping early

---
 packages/backend/src/misc/cache.ts | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/packages/backend/src/misc/cache.ts b/packages/backend/src/misc/cache.ts
index fc98ce8132..d968069ca3 100644
--- a/packages/backend/src/misc/cache.ts
+++ b/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,
@@ -289,10 +289,14 @@ 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) {
-				this.cache.delete(key);
-			}
+			// 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);
 		}
 	}