diff --git a/packages/backend/server/src/core/sync/gateway.ts b/packages/backend/server/src/core/sync/gateway.ts
index ade38a6a8e..e56dc87209 100644
--- a/packages/backend/server/src/core/sync/gateway.ts
+++ b/packages/backend/server/src/core/sync/gateway.ts
@@ -45,7 +45,9 @@ type EventResponse<Data = any> = Data extends never
       data: Data;
     };
 
-type RoomType = 'sync' | `${string}:awareness`;
+// 019 only receives space:broadcast-doc-updates and send space:push-doc-updates
+// 020 only receives space:broadcast-doc-update and send space:push-doc-update
+type RoomType = 'sync' | `${string}:awareness` | 'sync-019';
 
 function Room(
   spaceId: string,
@@ -214,7 +216,16 @@ export class SpaceSyncGateway
   ): Promise<EventResponse<{ clientId: string; success: true }>> {
     await this.assertVersion(client, clientVersion);
 
-    await this.selectAdapter(client, spaceType).join(user.id, spaceId);
+    // TODO(@forehalo): remove this after 0.19 goes out of life
+    // simple match 0.19.x
+    if (/^0.19.[\d]$/.test(clientVersion)) {
+      const room = Room(spaceId, 'sync-019');
+      if (!client.rooms.has(room)) {
+        await client.join(room);
+      }
+    } else {
+      await this.selectAdapter(client, spaceType).join(user.id, spaceId);
+    }
 
     return { data: { clientId: client.id, success: true } };
   }
@@ -270,6 +281,8 @@ export class SpaceSyncGateway
 
   /**
    * @deprecated use [space:push-doc-update] instead, client should always merge updates on their own
+   *
+   * only 0.19.x client will send this event
    */
   @SubscribeMessage('space:push-doc-updates')
   async onReceiveDocUpdates(
@@ -289,23 +302,19 @@ export class SpaceSyncGateway
       user.id
     );
 
-    // could be put in [adapter.push]
-    // but the event should be kept away from adapter
-    // so
+    // broadcast to 0.19.x clients
     client
-      .to(adapter.room(spaceId))
+      .to(Room(spaceId, 'sync-019'))
       .emit('space:broadcast-doc-updates', { ...message, timestamp });
 
-    // TODO(@forehalo): remove backward compatibility
-    if (spaceType === SpaceType.Workspace) {
-      const id = new DocID(docId, spaceId);
-      client.to(adapter.room(spaceId)).emit('server-updates', {
-        workspaceId: spaceId,
-        guid: id.guid,
-        updates,
+    // broadcast to new clients
+    updates.forEach(update => {
+      client.to(adapter.room(spaceId)).emit('space:broadcast-doc-update', {
+        ...message,
+        update,
         timestamp,
       });
-    }
+    });
 
     return {
       data: {
@@ -333,9 +342,8 @@ export class SpaceSyncGateway
       user.id
     );
 
-    // TODO(@forehalo): separate different version of clients into different rooms,
-    // so the clients won't receive useless updates events
-    client.to(adapter.room(spaceId)).emit('space:broadcast-doc-updates', {
+    // broadcast to 0.19.x clients
+    client.to(Room(spaceId, 'sync-019')).emit('space:broadcast-doc-updates', {
       spaceType,
       spaceId,
       docId,
@@ -445,163 +453,8 @@ export class SpaceSyncGateway
       .to(adapter.room(spaceId, roomType))
       .emit('space:broadcast-awareness-update', message);
 
-    // TODO(@forehalo): remove backward compatibility
-    if (spaceType === SpaceType.Workspace) {
-      client
-        .to(adapter.room(spaceId, roomType))
-        .emit('server-awareness-broadcast', {
-          workspaceId: spaceId,
-          awarenessUpdate: message.awarenessUpdate,
-        });
-    }
-
     return {};
   }
-
-  // TODO(@forehalo): remove
-  // deprecated section
-  @SubscribeMessage('client-handshake-sync')
-  async handleClientHandshakeSync(
-    @CurrentUser() user: CurrentUser,
-    @MessageBody('workspaceId') workspaceId: string,
-    @MessageBody('version') version: string,
-    @ConnectedSocket() client: Socket
-  ): Promise<EventResponse<{ clientId: string }>> {
-    await this.assertVersion(client, version);
-
-    return this.onJoinSpace(user, client, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      clientVersion: version,
-    });
-  }
-
-  @SubscribeMessage('client-leave-sync')
-  async handleLeaveSync(
-    @MessageBody() workspaceId: string,
-    @ConnectedSocket() client: Socket
-  ): Promise<EventResponse> {
-    return this.onLeaveSpace(client, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-    });
-  }
-
-  @SubscribeMessage('client-pre-sync')
-  async loadDocStats(
-    @ConnectedSocket() client: Socket,
-    @MessageBody()
-    { workspaceId, timestamp }: { workspaceId: string; timestamp?: number }
-  ): Promise<EventResponse<Record<string, number>>> {
-    return this.onLoadDocTimestamps(client, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      timestamp,
-    });
-  }
-
-  @SubscribeMessage('client-update-v2')
-  async handleClientUpdateV2(
-    @CurrentUser() user: CurrentUser,
-    @MessageBody()
-    {
-      workspaceId,
-      guid,
-      updates,
-    }: {
-      workspaceId: string;
-      guid: string;
-      updates: string[];
-    },
-    @ConnectedSocket() client: Socket
-  ): Promise<EventResponse<{ accepted: true; timestamp?: number }>> {
-    return this.onReceiveDocUpdates(client, user, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      docId: guid,
-      updates,
-    });
-  }
-
-  @SubscribeMessage('doc-load-v2')
-  async loadDocV2(
-    @ConnectedSocket() client: Socket,
-    @MessageBody()
-    {
-      workspaceId,
-      guid,
-      stateVector,
-    }: {
-      workspaceId: string;
-      guid: string;
-      stateVector?: string;
-    }
-  ): Promise<
-    EventResponse<{ missing: string; state?: string; timestamp: number }>
-  > {
-    return this.onLoadSpaceDoc(client, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      docId: guid,
-      stateVector,
-    });
-  }
-
-  @SubscribeMessage('client-handshake-awareness')
-  async handleClientHandshakeAwareness(
-    @ConnectedSocket() client: Socket,
-    @CurrentUser() user: CurrentUser,
-    @MessageBody('workspaceId') workspaceId: string,
-    @MessageBody('version') version: string
-  ): Promise<EventResponse<{ clientId: string }>> {
-    return this.onJoinAwareness(client, user, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      docId: workspaceId,
-      clientVersion: version,
-    });
-  }
-
-  @SubscribeMessage('client-leave-awareness')
-  async handleLeaveAwareness(
-    @MessageBody() workspaceId: string,
-    @ConnectedSocket() client: Socket
-  ): Promise<EventResponse> {
-    return this.onLeaveAwareness(client, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      docId: workspaceId,
-    });
-  }
-
-  @SubscribeMessage('awareness-init')
-  async handleInitAwareness(
-    @MessageBody() workspaceId: string,
-    @ConnectedSocket() client: Socket
-  ): Promise<EventResponse<{ clientId: string }>> {
-    return this.onLoadAwareness(client, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      docId: workspaceId,
-    });
-  }
-
-  @SubscribeMessage('awareness-update')
-  async handleHelpGatheringAwareness(
-    @MessageBody()
-    {
-      workspaceId,
-      awarenessUpdate,
-    }: { workspaceId: string; awarenessUpdate: string },
-    @ConnectedSocket() client: Socket
-  ): Promise<EventResponse> {
-    return this.onUpdateAwareness(client, {
-      spaceType: SpaceType.Workspace,
-      spaceId: workspaceId,
-      docId: workspaceId,
-      awarenessUpdate,
-    });
-  }
 }
 
 abstract class SyncSocketAdapter {
@@ -647,7 +500,8 @@ abstract class SyncSocketAdapter {
   ): Promise<void>;
 
   push(spaceId: string, docId: string, updates: Buffer[], editorId: string) {
-    this.assertIn(spaceId);
+    // TODO(@forehalo): enable this after 0.19 goes out of life
+    // this.assertIn(spaceId);
     return this.storage.pushDocUpdates(spaceId, docId, updates, editorId);
   }