Optimize caching of revisions/documents (immutable entries) in memory and cloudflare cache (#252)

* Better handle immutable cache entries in memory/cf-cache

* Format

* Update src/lib/cache/utils.ts

Co-authored-by: Steven H <shne24@gmail.com>

---------

Co-authored-by: Steven H <shne24@gmail.com>

src/lib/cache/cloudflare-cache.ts

@@ -3,11 +3,10 @@ import { Buffer } from 'node:buffer';
 import type { CacheStorage, Cache, Response as WorkerResponse } from '@cloudflare/workers-types';
 
 import { CacheBackend, CacheEntry } from './types';
-import { getCacheMaxAge } from './utils';
+import { getCacheMaxAge, isCacheEntryImmutable } from './utils';
 import { trace } from '../tracing';
 
 const cacheVersion = 1;
-const cacheMaxAge = 2 * 60;
 
 /**
  * Cache implementation using the Cloudflare Cache API.
@@ -102,8 +101,16 @@ function serializeEntry(entry: CacheEntry): WorkerResponse {
     headers.set('Content-Type', 'application/json');
     const cacheTags = ['gitbook-open', ...entry.meta.tags];
 
-    // Limit the cloudflare cache to a low fix duration
-    headers.set('Cache-Control', `public, max-age=${getCacheMaxAge(entry.meta, 10, cacheMaxAge)}`);
+    // When the entry is immutable, we can cache it for the entire duration.
+    // If the entry can be invalidated, we cache it for maximum 2 minutes as it could be invalidated in another data center.
+    headers.set(
+        'Cache-Control',
+        `public, max-age=${getCacheMaxAge(
+            entry.meta,
+            10,
+            isCacheEntryImmutable(entry.meta) ? 2 * 60 : undefined,
+        )}`,
+    );
     headers.set('Cache-Tag', cacheTags.join(','));
 
     // @ts-ignore

src/lib/cache/memory.ts

@@ -1,9 +1,5 @@
 import { CacheBackend, CacheEntry } from './types';
-
-/**
- * In production, we limit the cache to 5 minutes as it can't be invalidated on all instances.
- */
-const cacheMaxAge = process.env.NODE_ENV === 'development' ? Infinity : 5 * 60;
+import { isCacheEntryImmutable } from './utils';
 
 export const memoryCache: CacheBackend = {
     name: 'memory',
@@ -30,7 +26,16 @@ export const memoryCache: CacheBackend = {
             ...entry,
             meta: {
                 ...entry.meta,
-                expiresAt: Math.min(Date.now() + cacheMaxAge * 1000, entry.meta.expiresAt),
+                ...(isCacheEntryImmutable(entry.meta) || process.env.NODE_ENV === 'development'
+                    ? {}
+                    : {
+                          // For mutable entries, we limit the cache to 1 minute
+                          // as it could be invalidated at any time.
+                          expiresAt: Math.min(
+                              entry.meta.setAt ?? Date.now() + 60 * 1000,
+                              entry.meta.expiresAt,
+                          ),
+                      }),
             },
         });
     },

src/lib/cache/types.ts

@@ -22,7 +22,8 @@ export interface CacheEntryMeta {
     revalidatesAt?: number;
 
     /**
-     * Tags associated with the entry.
+     * Tags associated with the entry, used for revalidation.
+     * If no tags is present, the entry is considered immutable.
      */
     tags: string[];
 

src/lib/cache/utils.ts

@@ -12,3 +12,10 @@ export function getCacheMaxAge(meta: CacheEntryMeta, min?: number, max?: number)
 
     return maxAge;
 }
+
+/**
+ * Return true if a cache entry can be considered immutable.
+ */
+export function isCacheEntryImmutable(meta: CacheEntryMeta): boolean {
+    return !meta.tags || meta.tags.length === 0;
+}

src/lib/images.ts

@@ -50,7 +50,6 @@ export async function getResizedImageURL(
         return () => input;
     }
 
-
     const signature = await generateSignature(input);
     if (!signature) {
         return () => input;