Improve /all-chats performance by replacing Redis SCAN with per-user chat index (#1618)

Fixes OPS-3001.
This change will require a migration script to move all chatIds to
respective user index.

## Additional Notes
### Why /all-chats was slow

- Redis SCAN is O(n) and requires multiple passes.
- It scans all keys, not only chat keys.
- Each chat key triggered a separate GET, causing N+1 calls.

### How it’s now improved

- Each user has a dedicated Redis Set storing their chat IDs.
- Lookup becomes O(1) via SMEMBERS.

Author: ravikiranvm

packages/server/api/src/app/ai/chat/ai-chat.service.ts

@@ -58,6 +58,8 @@ export type MCPChatContext = {
   model?: string;
 };
 
+type ChatSummary = { chatId: string; chatName: string };
+
 export const generateChatId = (
   params: MCPChatContext & {
     userId: string;
@@ -122,6 +124,10 @@ export const updateChatName = async (
   await createChatContext(chatId, userId, projectId, updatedChatContext);
 };
 
+const userChatsIndexKey = (userId: string, projectId: string): string => {
+  return `${projectId}:${userId}:chats`;
+};
+
 export const createChatContext = async (
   chatId: string,
   userId: string,
@@ -136,6 +142,8 @@ export const createChatContext = async (
     context,
     chatExpireTime,
   );
+  const indexKey = userChatsIndexKey(userId, projectId);
+  await cacheWrapper.addToSet(indexKey, chatId);
 };
 
 export const getChatContext = async (
@@ -176,28 +184,27 @@ export const getAllChats = async (
   userId: string,
   projectId: string,
 ): Promise<{ chatId: string; chatName: string }[]> => {
-  const pattern = `${projectId}:${userId}:*:context`;
-  const keys = await cacheWrapper.scanKeys(pattern);
-  const chats: { chatId: string; chatName: string }[] = [];
-
-  for (const key of keys) {
-    const keyParts = key.split(':');
-    if (keyParts.length !== 4) {
-      continue;
-    }
-    const longChatId = keyParts[2];
-
-    const context = await cacheWrapper.getSerializedObject<MCPChatContext>(key);
-
-    if (context?.chatName) {
-      chats.push({
-        chatId: longChatId,
-        chatName: context.chatName,
-      });
-    }
+  const indexKey = userChatsIndexKey(userId, projectId);
+  const chatIds = await cacheWrapper.getSetMembers(indexKey);
+
+  if (chatIds.length === 0) {
+    return [];
   }
 
-  return chats;
+  const chatsOrNull = await Promise.all(
+    chatIds.map(async (chatId): Promise<ChatSummary | null> => {
+      const context = await getChatContext(chatId, userId, projectId);
+      if (!context?.chatName) {
+        return null;
+      }
+      return {
+        chatId,
+        chatName: context.chatName,
+      };
+    }),
+  );
+
+  return chatsOrNull.filter((chat): chat is ChatSummary => chat !== null);
 };
 
 export const saveChatHistory = async (
@@ -221,10 +228,12 @@ export const deleteChatHistory = async (
   userId: string,
   projectId: string,
 ): Promise<void> => {
+  const indexKey = userChatsIndexKey(userId, projectId);
   await Promise.all([
     cacheWrapper.deleteKey(chatHistoryKey(chatId, userId, projectId)),
     cacheWrapper.deleteKey(chatToolsKey(chatId, userId, projectId)),
     cacheWrapper.deleteKey(chatContextKey(chatId, userId, projectId)),
+    cacheWrapper.removeFromSet(indexKey, chatId),
   ]);
 };
 

packages/server/shared/src/lib/cache/memory-wrapper.ts

@@ -73,6 +73,24 @@ const getBufferAndDelete = async (key: string): Promise<Buffer | null> => {
   throw new Error('Not implemented');
 };
 
+const addToSet = async (key: string, member: string): Promise<void> => {
+  const existing = (await getSerializedObject<string[]>(key)) ?? [];
+  if (!existing.includes(member)) {
+    existing.push(member);
+  }
+  await setSerializedObject(key, existing);
+};
+
+const removeFromSet = async (key: string, member: string): Promise<void> => {
+  const existing = (await getSerializedObject<string[]>(key)) ?? [];
+  const updated = existing.filter((id) => id !== member);
+  await setSerializedObject(key, updated);
+};
+
+const getSetMembers = async (key: string): Promise<string[]> => {
+  return (await getSerializedObject<string[]>(key)) ?? [];
+};
+
 export const memoryWrapper = {
   setKey,
   getKey,
@@ -84,4 +102,7 @@ export const memoryWrapper = {
   setSerializedObject,
   getSerializedObject,
   scanKeys,
+  addToSet,
+  removeFromSet,
+  getSetMembers,
 };

packages/server/shared/src/lib/cache/redis-wrapper.ts

@@ -59,6 +59,21 @@ async function setSerializedObject<T>(
   await setKey(key, JSON.stringify(obj), expireInSeconds);
 }
 
+const addToSet = async (key: string, member: string): Promise<void> => {
+  const redis = getRedisClient();
+  await redis.sadd(key, member);
+};
+
+const removeFromSet = async (key: string, member: string): Promise<void> => {
+  const redis = getRedisClient();
+  await redis.srem(key, member);
+};
+
+const getSetMembers = async (key: string): Promise<string[]> => {
+  const redis = getRedisClient();
+  return redis.smembers(key);
+};
+
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 async function getOrAdd<T, Args extends any[]>(
   key: string,
@@ -134,4 +149,7 @@ export const redisWrapper = {
   setSerializedObject,
   getSerializedObject,
   scanKeys,
+  addToSet,
+  removeFromSet,
+  getSetMembers,
 };