PERF: Use `MessageBus.last_ids` instead of `MessageBus.last_id` for chat (#19523)

Prior to this change, each request executed 2 Redis calls per chat channel
that was loaded. The number of Redis calls quickly adds up once a user
is following multiple channels.

plugins/chat/app/serializers/chat_channel_serializer.rb

@@ -24,6 +24,8 @@ class ChatChannelSerializer < ApplicationSerializer
 
   def initialize(object, opts)
     super(object, opts)
+
+    @opts = opts
     @current_user_membership = opts[:membership]
   end
 
@@ -98,8 +100,8 @@ class ChatChannelSerializer < ApplicationSerializer
 
   def message_bus_last_ids
     {
-      new_messages: MessageBus.last_id("/chat/#{object.id}/new-messages"),
-      new_mentions: MessageBus.last_id("/chat/#{object.id}/new-mentions"),
+      new_messages: @opts[:new_messages_message_bus_last_id] || MessageBus.last_id(ChatPublisher.new_messages_message_bus_channel(object.id)),
+      new_mentions: @opts[:new_mentions_message_bus_last_id] || MessageBus.last_id(ChatPublisher.new_mentions_message_bus_channel(object.id)),
     }
   end
 

plugins/chat/app/serializers/structured_channel_serializer.rb

@@ -10,6 +10,8 @@ class StructuredChannelSerializer < ApplicationSerializer
         root: nil,
         scope: scope,
         membership: channel_membership(channel.id),
+        new_messages_message_bus_last_id: chat_message_bus_last_ids[ChatPublisher.new_messages_message_bus_channel(channel.id)],
+        new_mentions_message_bus_last_id: chat_message_bus_last_ids[ChatPublisher.new_mentions_message_bus_channel(channel.id)]
       )
     end
   end
@@ -21,6 +23,8 @@ class StructuredChannelSerializer < ApplicationSerializer
         root: nil,
         scope: scope,
         membership: channel_membership(channel.id),
+        new_messages_message_bus_last_id: chat_message_bus_last_ids[ChatPublisher.new_messages_message_bus_channel(channel.id)],
+        new_mentions_message_bus_last_id: chat_message_bus_last_ids[ChatPublisher.new_mentions_message_bus_channel(channel.id)]
       )
     end
   end
@@ -31,17 +35,46 @@ class StructuredChannelSerializer < ApplicationSerializer
   end
 
   def message_bus_last_ids
-    last_ids = {
-      channel_metadata: MessageBus.last_id("/chat/channel-metadata"),
-      channel_edits: MessageBus.last_id("/chat/channel-edits"),
-      channel_status: MessageBus.last_id("/chat/channel-status"),
-      new_channel: MessageBus.last_id("/chat/new-channel"),
+    ids = {
+      channel_metadata: chat_message_bus_last_ids[ChatPublisher::CHANNEL_METADATA_MESSAGE_BUS_CHANNEL],
+      channel_edits: chat_message_bus_last_ids[ChatPublisher::CHANNEL_EDITS_MESSAGE_BUS_CHANNEL],
+      channel_status: chat_message_bus_last_ids[ChatPublisher::CHANNEL_STATUS_MESSAGE_BUS_CHANNEL],
+      new_channel: chat_message_bus_last_ids[ChatPublisher::NEW_CHANNEL_MESSAGE_BUS_CHANNEL]
     }
-    if !scope.anonymous?
-      last_ids[:user_tracking_state] = MessageBus.last_id(
-        "/chat/user-tracking-state/#{scope.user.id}",
-      )
+
+    if id = chat_message_bus_last_ids[ChatPublisher.user_tracking_state_message_bus_channel(scope.user.id)]
+      ids[:user_tracking_state] = id
+    end
+
+    ids
+  end
+
+  private
+
+  def chat_message_bus_last_ids
+    @chat_message_bus_last_ids ||= begin
+      message_bus_channels = [
+        ChatPublisher::CHANNEL_METADATA_MESSAGE_BUS_CHANNEL,
+        ChatPublisher::CHANNEL_EDITS_MESSAGE_BUS_CHANNEL,
+        ChatPublisher::CHANNEL_STATUS_MESSAGE_BUS_CHANNEL,
+        ChatPublisher::NEW_CHANNEL_MESSAGE_BUS_CHANNEL,
+      ]
+
+      if !scope.anonymous?
+        message_bus_channels.push(ChatPublisher.user_tracking_state_message_bus_channel(scope.user.id))
+      end
+
+      object[:public_channels].each do |channel|
+        message_bus_channels.push(ChatPublisher.new_messages_message_bus_channel(channel.id))
+        message_bus_channels.push(ChatPublisher.new_mentions_message_bus_channel(channel.id))
+      end
+
+      object[:direct_message_channels].each do |channel|
+        message_bus_channels.push(ChatPublisher.new_messages_message_bus_channel(channel.id))
+        message_bus_channels.push(ChatPublisher.new_mentions_message_bus_channel(channel.id))
+      end
+
+      MessageBus.last_ids(*message_bus_channels)
     end
-    last_ids
   end
 end

plugins/chat/app/services/chat_publisher.rb

@@ -1,6 +1,10 @@
 # frozen_string_literal: true
 
 module ChatPublisher
+  def self.new_messages_message_bus_channel(chat_channel_id)
+    "/chat/#{chat_channel_id}/new-messages"
+  end
+
   def self.publish_new!(chat_channel, chat_message, staged_id)
     content =
       ChatMessageSerializer.new(
@@ -10,9 +14,11 @@ module ChatPublisher
     content[:type] = :sent
     content[:stagedId] = staged_id
     permissions = permissions(chat_channel)
+
     MessageBus.publish("/chat/#{chat_channel.id}", content.as_json, permissions)
+
     MessageBus.publish(
-      "/chat/#{chat_channel.id}/new-messages",
+      self.new_messages_message_bus_channel(chat_channel.id),
       {
         message_id: chat_message.id,
         user_id: chat_message.user.id,
@@ -120,22 +126,32 @@ module ChatPublisher
     )
   end
 
+  def self.user_tracking_state_message_bus_channel(user_id)
+    "/chat/user-tracking-state/#{user_id}"
+  end
+
   def self.publish_user_tracking_state(user, chat_channel_id, chat_message_id)
     MessageBus.publish(
-      "/chat/user-tracking-state/#{user.id}",
+      self.user_tracking_state_message_bus_channel(user.id),
       { chat_channel_id: chat_channel_id, chat_message_id: chat_message_id.to_i }.as_json,
       user_ids: [user.id],
     )
   end
 
+  def self.new_mentions_message_bus_channel(chat_channel_id)
+    "/chat/#{chat_channel_id}/new-mentions"
+  end
+
   def self.publish_new_mention(user_id, chat_channel_id, chat_message_id)
     MessageBus.publish(
-      "/chat/#{chat_channel_id}/new-mentions",
+      self.new_mentions_message_bus_channel(chat_channel_id),
       { message_id: chat_message_id }.as_json,
       user_ids: [user_id],
     )
   end
 
+  NEW_CHANNEL_MESSAGE_BUS_CHANNEL = "/chat/new-channel"
+
   def self.publish_new_channel(chat_channel, users)
     users.each do |user|
       serialized_channel =
@@ -145,7 +161,7 @@ module ChatPublisher
           root: :chat_channel,
           membership: chat_channel.membership_for(user),
         ).as_json
-      MessageBus.publish("/chat/new-channel", serialized_channel, user_ids: [user.id])
+      MessageBus.publish(NEW_CHANNEL_MESSAGE_BUS_CHANNEL, serialized_channel, user_ids: [user.id])
     end
   end
 
@@ -171,9 +187,11 @@ module ChatPublisher
     )
   end
 
+  CHANNEL_EDITS_MESSAGE_BUS_CHANNEL = "/chat/channel-edits"
+
   def self.publish_chat_channel_edit(chat_channel, acting_user)
     MessageBus.publish(
-      "/chat/channel-edits",
+      CHANNEL_EDITS_MESSAGE_BUS_CHANNEL,
       {
         chat_channel_id: chat_channel.id,
         name: chat_channel.title(acting_user),
@@ -183,17 +201,21 @@ module ChatPublisher
     )
   end
 
+  CHANNEL_STATUS_MESSAGE_BUS_CHANNEL = "/chat/channel-status"
+
   def self.publish_channel_status(chat_channel)
     MessageBus.publish(
-      "/chat/channel-status",
+      CHANNEL_STATUS_MESSAGE_BUS_CHANNEL,
       { chat_channel_id: chat_channel.id, status: chat_channel.status },
       permissions(chat_channel),
     )
   end
 
+  CHANNEL_METADATA_MESSAGE_BUS_CHANNEL = "/chat/channel-metadata"
+
   def self.publish_chat_channel_metadata(chat_channel)
     MessageBus.publish(
-      "/chat/channel-metadata",
+      CHANNEL_METADATA_MESSAGE_BUS_CHANNEL,
       { chat_channel_id: chat_channel.id, memberships_count: chat_channel.user_count },
       permissions(chat_channel),
     )