add lru cache

Author: blva

package-lock.json

@@ -62,6 +62,7 @@
     "@mongodb-js/devtools-connect": "^3.7.2",
     "@mongosh/service-provider-node-driver": "^3.6.0",
     "bson": "^6.10.3",
+    "lru-cache": "^11.1.0",
     "mongodb": "^6.15.0",
     "mongodb-log-writer": "^2.4.1",
     "mongodb-redact": "^1.1.6",

package.json

@@ -1,14 +1,26 @@
 import { BaseEvent } from "./types.js";
+import { LRUCache } from "lru-cache";
 
 /**
  * Singleton class for in-memory telemetry event caching
  * Provides a central storage for telemetry events that couldn't be sent
+ * Uses LRU cache to automatically drop oldest events when limit is exceeded
  */
 export class EventCache {
     private static instance: EventCache;
-    private events: BaseEvent[] = [];
+    private static readonly MAX_EVENTS = 1000;
 
-    private constructor() {}
+    private cache: LRUCache<number, BaseEvent>;
+    private nextId = 0;
+
+    private constructor() {
+        this.cache = new LRUCache({
+            max: EventCache.MAX_EVENTS,
+            // Using FIFO eviction strategy for events
+            allowStale: false,
+            updateAgeOnGet: false,
+        });
+    }
 
     /**
      * Gets the singleton instance of EventCache
@@ -26,21 +38,25 @@ export class EventCache {
      * @returns Array of cached BaseEvent objects
      */
     public getEvents(): BaseEvent[] {
-        return [...this.events];
+        return Array.from(this.cache.values());
     }
 
     /**
-     * Sets the cached events, replacing any existing events
-     * @param events - The events to cache
+     * Appends new events to the cached events
+     * LRU cache automatically handles dropping oldest events when limit is exceeded
+     * @param events - The events to append
      */
-    public setEvents(events: BaseEvent[]): void {
-        this.events = [...events];
+    public appendEvents(events: BaseEvent[]): void {
+        for (const event of events) {
+            this.cache.set(this.nextId++, event);
+        }
     }
 
     /**
      * Clears all cached events
      */
     public clearEvents(): void {
-        this.events = [];
+        this.cache.clear();
+        this.nextId = 0;
     }
 }

src/telemetry/eventCache.ts

@@ -110,8 +110,12 @@ export class Telemetry {
             return;
         }
 
-        logger.warning(mongoLogId(1_000_005), "telemetry", `Error sending event to client: ${result.error}`);
-        this.eventCache.setEvents(allEvents);
+        logger.warning(
+            mongoLogId(1_000_005), 
+            "telemetry", 
+            `Error sending event to client: ${result.error instanceof Error ? result.error.message : String(result.error)}`
+        );
+        this.eventCache.appendEvents(events);
     }
 
     /**