Cache loading and update optimization (#756)

.changeset/fast-points-count.md

@@ -0,0 +1,5 @@
+---
+'@cloudflare/next-on-pages': minor
+---
+
+Optimized cache tags manifest loading; cache updates do not block responses

packages/next-on-pages/templates/_worker.js/utils/cache.ts

@@ -6,6 +6,8 @@ const CACHE_TAGS_HEADER = 'x-vercel-cache-tags';
 // https://github.com/vercel/next.js/blob/ba23d986/packages/next/src/lib/constants.ts#L18
 const NEXT_CACHE_SOFT_TAGS_HEADER = 'x-next-cache-soft-tags';
 
+const REQUEST_CONTEXT_KEY = Symbol.for('__cloudflare-request-context__');
+
 /**
  * Handles an internal request to the suspense cache.
  *
@@ -58,15 +60,29 @@ export async function handleSuspenseCacheRequest(request: Request) {
 				});
 			}
 			case 'POST': {
-				// Update the value in the cache.
-				const body = await request.json<IncrementalCacheValue>();
-				// Falling back to the cache tags header for Next.js 13.5+
-				if (body.data.tags === undefined) {
-					body.tags ??= getTagsFromHeader(request, CACHE_TAGS_HEADER) ?? [];
+				// Retrieve request context.
+				const reqCtx = (globalThis as unknown as Record<symbol, unknown>)[
+					REQUEST_CONTEXT_KEY
+				] as { ctx: ExecutionContext };
+
+				const update = async () => {
+					// Update the value in the cache.
+					const body = await request.json<IncrementalCacheValue>();
+					// Falling back to the cache tags header for Next.js 13.5+
+					if (body.data.tags === undefined) {
+						body.tags ??= getTagsFromHeader(request, CACHE_TAGS_HEADER) ?? [];
+					}
+
+					await cache.set(cacheKey, body);
+				};
+
+				if (reqCtx) {
+					// Avoid waiting for the cache to update before responding, if possible.
+					reqCtx.ctx.waitUntil(update());
+				} else {
+					await update();
 				}
 
-				await cache.set(cacheKey, body);
-
 				return new Response(null, { status: 200 });
 			}
 			default:

packages/next-on-pages/templates/cache/adaptor.ts

@@ -13,6 +13,8 @@ export class CacheAdaptor {
 	public tagsManifest: TagsManifest | undefined;
 	/** The key used for the tags manifest in the cache. */
 	public tagsManifestKey = 'tags-manifest';
+	/** Promise that resolves when tags manifest is loaded */
+	public tagsManifestPromise: Promise<void> | undefined;
 
 	/**
 	 * @param ctx The incremental cache context from Next.js. NOTE: This is not currently utilised in NOP.
@@ -52,7 +54,7 @@ export class CacheAdaptor {
 		};
 
 		// Update the cache entry.
-		await this.update(key, JSON.stringify(newEntry));
+		const updateOp = this.update(key, JSON.stringify(newEntry));
 
 		switch (newEntry.value?.kind) {
 			case 'FETCH': {
@@ -70,6 +72,9 @@ export class CacheAdaptor {
 				);
 			}
 		}
+
+		// Make sure the cache has been updated before returning
+		await updateOp;
 	}
 
 	/**
@@ -84,7 +89,12 @@ export class CacheAdaptor {
 		{ softTags }: { softTags?: string[] },
 	): Promise<CacheHandlerValue | null> {
 		// Get entry from the cache.
-		const entry = await this.retrieve(key);
+		const entryPromise = this.retrieve(key);
+
+		// Start loading the tags manifest.
+		const tagsManifestLoad = this.loadTagsManifest();
+
+		const entry = await entryPromise;
 		if (!entry) return null;
 
 		let data: CacheHandlerValue;
@@ -97,8 +107,8 @@ export class CacheAdaptor {
 
 		switch (data.value?.kind) {
 			case 'FETCH': {
-				// Load the tags manifest.
-				await this.loadTagsManifest();
+				// Await for the tags manifest to end loading.
+				await tagsManifestLoad;
 
 				// Check if the cache entry is stale or fresh based on the tags.
 				const tags = getTagsFromEntry(data);
@@ -140,8 +150,29 @@ export class CacheAdaptor {
 
 	/**
 	 * Loads the tags manifest from the suspense cache.
+	 *
+	 * @param force Whether to force a reload of the tags manifest.
+	 */
+	public async loadTagsManifest(force = false): Promise<void> {
+		// Load tags manifest if missing or refresh if forced.
+		const shouldLoad = force || !this.tagsManifest;
+
+		if (!shouldLoad) {
+			return;
+		}
+
+		// If the tags manifest is not already being loaded, kickstart the retrieval.
+		if (!this.tagsManifestPromise) {
+			this.tagsManifestPromise = this.loadTagsManifestInternal();
+		}
+
+		await this.tagsManifestPromise;
+	}
+
+	/**
+	 * Internal method to load the tags manifest from the suspense cache.
 	 */
-	public async loadTagsManifest(): Promise<void> {
+	private async loadTagsManifestInternal(): Promise<void> {
 		try {
 			const rawManifest = await this.retrieve(this.tagsManifestKey);
 			if (rawManifest) {
@@ -152,6 +183,7 @@ export class CacheAdaptor {
 		}
 
 		this.tagsManifest ??= { version: 1, items: {} };
+		this.tagsManifestPromise = undefined;
 	}
 
 	/**
@@ -174,7 +206,7 @@ export class CacheAdaptor {
 		tags: string[],
 		{ cacheKey, revalidatedAt }: { cacheKey?: string; revalidatedAt?: number },
 	): Promise<void> {
-		await this.loadTagsManifest();
+		await this.loadTagsManifest(true);
 
 		// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
 		const tagsManifest = this.tagsManifest!;