added comment

Author: conico974

packages/open-next/src/overrides/incrementalCache/multi-tier-ddb-s3.ts

@@ -100,6 +100,10 @@ const multiTierCache: IncrementalCache = {
     }
     return result;
   },
+
+  // Both for set and delete we choose to do the write to S3 first and then to DynamoDB
+  // Which means that if it fails in DynamoDB, instance that don't have local cache will work as expected.
+  // But instance that have local cache will have a stale cache until the next working set or delete.
   async set(key, value, isFetch) {
     const revalidatedAt = Date.now();
     await S3Cache.set(key, value, isFetch);

packages/open-next/src/utils/lru.ts

@@ -5,7 +5,9 @@ export class LRUCache<T> {
 
   get(key: string) {
     const result = this.cache.get(key);
+    // We could have used .has to allow for nullish value to be stored but we don't need that right now
     if (result) {
+      // By removing and setting the key again we ensure it's the most recently used
       this.cache.delete(key);
       this.cache.set(key, result);
     }