Optimize tag writing process (#911)

* only call tag cache once

* write tags right away instead of at the end of the request

* read from pending write in composable cache

* fix unit test

* review fix

---------

Co-authored-by: Nicolas Dorseuil <nicolas@gitbook.io>

Author: conico974

packages/open-next/src/adapters/cache.ts

@@ -3,7 +3,7 @@ import type {
   IncrementalCacheContext,
   IncrementalCacheValue,
 } from "types/cache";
-import { getTagsFromValue, hasBeenRevalidated } from "utils/cache";
+import { getTagsFromValue, hasBeenRevalidated, writeTags } from "utils/cache";
 import { isBinaryContentType } from "../utils/binary";
 import { debug, error, warn } from "./logger";
 
@@ -326,7 +326,7 @@ export default class Cache {
       if (globalThis.tagCache.mode === "nextMode") {
         const paths = (await globalThis.tagCache.getPathsByTags?.(_tags)) ?? [];
 
-        await globalThis.tagCache.writeTags(_tags);
+        await writeTags(_tags);
         if (paths.length > 0) {
           // TODO: we should introduce a new method in cdnInvalidationHandler to invalidate paths by tags for cdn that supports it
           // It also means that we'll need to provide the tags used in every request to the wrapper or converter.
@@ -378,7 +378,7 @@ export default class Cache {
         }
 
         // Update all keys with the given tag with revalidatedAt set to now
-        await globalThis.tagCache.writeTags(toInsert);
+        await writeTags(toInsert);
 
         // We can now invalidate all paths in the CDN
         // This only applies to `revalidateTag`, not to `res.revalidate()`
@@ -442,7 +442,7 @@ export default class Cache {
     const storedTags = await globalThis.tagCache.getByPath(key);
     const tagsToWrite = derivedTags.filter((tag) => !storedTags.includes(tag));
     if (tagsToWrite.length > 0) {
-      await globalThis.tagCache.writeTags(
+      await writeTags(
         tagsToWrite.map((tag) => ({
           path: key,
           tag: tag,

packages/open-next/src/adapters/composable-cache.ts

@@ -1,10 +1,18 @@
 import type { ComposableCacheEntry, ComposableCacheHandler } from "types/cache";
+import { writeTags } from "utils/cache";
 import { fromReadableStream, toReadableStream } from "utils/stream";
 import { debug } from "./logger";
 
+const pendingWritePromiseMap = new Map<string, Promise<ComposableCacheEntry>>();
+
 export default {
   async get(cacheKey: string) {
     try {
+      // We first check if we have a pending write for this cache key
+      // If we do, we return the pending promise instead of fetching the cache
+      if (pendingWritePromiseMap.has(cacheKey)) {
+        return pendingWritePromiseMap.get(cacheKey);
+      }
       const result = await globalThis.incrementalCache.get(
         cacheKey,
         "composable",
@@ -48,7 +56,10 @@ export default {
   },
 
   async set(cacheKey: string, pendingEntry: Promise<ComposableCacheEntry>) {
-    const entry = await pendingEntry;
+    pendingWritePromiseMap.set(cacheKey, pendingEntry);
+    const entry = await pendingEntry.finally(() => {
+      pendingWritePromiseMap.delete(cacheKey);
+    });
     const valueToStore = await fromReadableStream(entry.value);
     await globalThis.incrementalCache.set(
       cacheKey,
@@ -62,9 +73,7 @@ export default {
       const storedTags = await globalThis.tagCache.getByPath(cacheKey);
       const tagsToWrite = entry.tags.filter((tag) => !storedTags.includes(tag));
       if (tagsToWrite.length > 0) {
-        await globalThis.tagCache.writeTags(
-          tagsToWrite.map((tag) => ({ tag, path: cacheKey })),
-        );
+        await writeTags(tagsToWrite.map((tag) => ({ tag, path: cacheKey })));
       }
     }
   },
@@ -83,7 +92,7 @@ export default {
   },
   async expireTags(...tags: string[]) {
     if (globalThis.tagCache.mode === "nextMode") {
-      return globalThis.tagCache.writeTags(tags);
+      return writeTags(tags);
     }
     const tagCache = globalThis.tagCache;
     const revalidatedAt = Date.now();
@@ -104,7 +113,7 @@ export default {
     for (const entry of pathsToUpdate.flat()) {
       setToWrite.add(entry);
     }
-    await globalThis.tagCache.writeTags(Array.from(setToWrite));
+    await writeTags(Array.from(setToWrite));
   },
 
   // This one is necessary for older versions of next

packages/open-next/src/types/global.ts

@@ -63,6 +63,8 @@ interface OpenNextRequestContext {
   // Last modified time of the page (used in main functions, only available for ISR/SSG).
   lastModified?: number;
   waitUntil?: WaitUntil;
+  /** We use this to deduplicate write of the tags*/
+  writtenTags: Set<string>;
 }
 
 declare global {

packages/open-next/src/types/overrides.ts

@@ -144,6 +144,12 @@ export type NextModeTagCache = BaseTagCache & {
   getPathsByTags?: (tags: string[]) => Promise<string[]>;
 };
 
+export interface OriginalTagCacheWriteInput {
+  tag: string;
+  path: string;
+  revalidatedAt?: number;
+}
+
 /**
  * On get :
 We just check for the cache key in the tag cache. If it has been revalidated we just return null, otherwise we continue
@@ -168,9 +174,7 @@ export type OriginalTagCache = BaseTagCache & {
   getByTag(tag: string): Promise<string[]>;
   getByPath(path: string): Promise<string[]>;
   getLastModified(path: string, lastModified?: number): Promise<number>;
-  writeTags(
-    tags: { tag: string; path: string; revalidatedAt?: number }[],
-  ): Promise<void>;
+  writeTags(tags: OriginalTagCacheWriteInput[]): Promise<void>;
 };
 
 export type TagCache = NextModeTagCache | OriginalTagCache;

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

@@ -1,4 +1,9 @@
-import type { CacheValue, WithLastModified } from "types/overrides";
+import type {
+  CacheValue,
+  OriginalTagCacheWriteInput,
+  WithLastModified,
+} from "types/overrides";
+import { debug } from "../adapters/logger";
 
 export async function hasBeenRevalidated(
   key: string,
@@ -39,3 +44,39 @@ export function getTagsFromValue(value?: CacheValue<"cache">) {
     return [];
   }
 }
+
+function getTagKey(tag: string | OriginalTagCacheWriteInput): string {
+  if (typeof tag === "string") {
+    return tag;
+  }
+  return JSON.stringify({
+    tag: tag.tag,
+    path: tag.path,
+  });
+}
+
+export async function writeTags(
+  tags: (string | OriginalTagCacheWriteInput)[],
+): Promise<void> {
+  const store = globalThis.__openNextAls.getStore();
+  debug("Writing tags", tags, store);
+  if (!store || globalThis.openNextConfig.dangerous?.disableTagCache) {
+    return;
+  }
+  const tagsToWrite = tags.filter((t) => {
+    const tagKey = getTagKey(t);
+    const shouldWrite = !store.writtenTags.has(tagKey);
+    // We preemptively add the tag to the writtenTags set
+    // to avoid writing the same tag multiple times in the same request
+    if (shouldWrite) {
+      store.writtenTags.add(tagKey);
+    }
+    return shouldWrite;
+  });
+  if (tagsToWrite.length === 0) {
+    return;
+  }
+
+  // Here we know that we have the correct type
+  await globalThis.tagCache.writeTags(tagsToWrite as any);
+}

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

@@ -119,6 +119,7 @@ export function runWithOpenNextRequestContext<T>(
       pendingPromiseRunner: new DetachedPromiseRunner(),
       isISRRevalidation,
       waitUntil,
+      writtenTags: new Set<string>(),
     },
     async () => {
       provideNextAfterProvider();

packages/tests-unit/tests/adapters/cache.test.ts

@@ -56,6 +56,7 @@ describe("CacheHandler", () => {
           resolve: vi.fn(),
         }),
       },
+      writtenTags: new Set(),
     }),
   };