Add caching for payload serialization during fan-out (#19642)

app/lib/inline_renderer.rb

@@ -11,6 +11,7 @@ class InlineRenderer
     case @template
     when :status
       serializer = REST::StatusSerializer
+      preload_associations_for_status
     when :notification
       serializer = REST::NotificationSerializer
     when :conversation
@@ -35,6 +36,16 @@ class InlineRenderer
 
   private
 
+  def preload_associations_for_status
+    ActiveRecord::Associations::Preloader.new.preload(@object, {
+      active_mentions: :account,
+
+      reblog: {
+        active_mentions: :account,
+      },
+    })
+  end
+
   def current_user
     @current_account&.user
   end

app/lib/status_cache_hydrator.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+class StatusCacheHydrator
+  def initialize(status)
+    @status = status
+  end
+
+  def hydrate(account_id)
+    # The cache of the serialized hash is generated by the fan-out-on-write service
+    payload = Rails.cache.fetch("fan-out/#{@status.id}") { InlineRenderer.render(@status, nil, :status) }
+
+    # If we're delivering to the author who disabled the display of the application used to create the
+    # status, we need to hydrate the application, since it was not rendered for the basic payload
+    payload[:application] = ActiveModelSerializers::SerializableResource.new(@status.application, serializer: REST::StatusSerializer::ApplicationSerializer).as_json if payload[:application].nil? && @status.account_id == account_id
+
+    # We take advantage of the fact that some relationships can only occur with an original status, not
+    # the reblog that wraps it, so we can assume that some values are always false
+    if payload[:reblog]
+      payload[:favourited] = false
+      payload[:reblogged]  = false
+      payload[:muted]      = false
+      payload[:bookmarked] = false
+      payload[:pinned]     = false
+      payload[:filtered]   = CustomFilter.apply_cached_filters(CustomFilter.cached_filters_for(@status.reblog_of_id), @status.reblog).map { |filter| ActiveModelSerializers::SerializableResource.new(filter, serializer: REST::FilterResultSerializer).as_json }
+
+      # If the reblogged status is being delivered to the author who disabled the display of the application
+      # used to create the status, we need to hydrate it here too
+      payload[:reblog][:application] = ActiveModelSerializers::SerializableResource.new(@status.reblog.application, serializer: REST::StatusSerializer::ApplicationSerializer).as_json if payload[:reblog][:application].nil? && @status.reblog.account_id == account_id
+
+      payload[:reblog][:favourited] = Favourite.where(account_id: account_id, status_id: @status.reblog_of_id).exists?
+      payload[:reblog][:reblogged]  = Status.where(account_id: account_id, reblog_of_id: @status.reblog_of_id).exists?
+      payload[:reblog][:muted]      = ConversationMute.where(account_id: account_id, conversation_id: @status.reblog.conversation_id).exists?
+      payload[:reblog][:bookmarked] = Bookmark.where(account_id: account_id, status_id: @status.reblog_of_id).exists?
+      payload[:reblog][:pinned]     = StatusPin.where(account_id: account_id, status_id: @status.reblog_of_id).exists?
+      payload[:reblog][:filtered]   = payload[:filtered]
+    else
+      payload[:favourited] = Favourite.where(account_id: account_id, status_id: @status.id).exists?
+      payload[:reblogged]  = Status.where(account_id: account_id, reblog_of_id: @status.id).exists?
+      payload[:muted]      = ConversationMute.where(account_id: account_id, conversation_id: @status.conversation_id).exists?
+      payload[:bookmarked] = Bookmark.where(account_id: account_id, status_id: @status.id).exists?
+      payload[:pinned]     = StatusPin.where(account_id: account_id, status_id: @status.id).exists?
+      payload[:filtered]   = CustomFilter.apply_cached_filters(CustomFilter.cached_filters_for(@status.id), @status).map { |filter| ActiveModelSerializers::SerializableResource.new(filter, serializer: REST::FilterResultSerializer).as_json }
+    end
+
+    payload
+  end
+end

app/services/fan_out_on_write_service.rb

@@ -14,6 +14,7 @@ class FanOutOnWriteService < BaseService
     @options   = options
 
     check_race_condition!
+    warm_payload_cache!
 
     fan_out_to_local_recipients!
     fan_out_to_public_recipients! if broadcastable?
@@ -135,13 +136,21 @@ class FanOutOnWriteService < BaseService
     AccountConversation.add_status(@account, @status) unless update?
   end
 
+  def warm_payload_cache!
+    Rails.cache.write("fan-out/#{@status.id}", rendered_status)
+  end
+
   def anonymous_payload
     @anonymous_payload ||= Oj.dump(
       event: update? ? :'status.update' : :update,
-      payload: InlineRenderer.render(@status, nil, :status)
+      payload: rendered_status
     )
   end
 
+  def rendered_status
+    @rendered_status ||= InlineRenderer.render(@status, nil, :status)
+  end
+
   def update?
     @options[:update]
   end

app/workers/push_update_worker.rb

@@ -5,11 +5,12 @@ class PushUpdateWorker
   include Redisable
 
   def perform(account_id, status_id, timeline_id = nil, options = {})
-    @account     = Account.find(account_id)
-    @status      = Status.includes(active_mentions: :account, reblog: { active_mentions: :account }).find(status_id)
-    @timeline_id = timeline_id || "timeline:#{account.id}"
+    @status      = Status.find(status_id)
+    @account_id  = account_id
+    @timeline_id = timeline_id || "timeline:#{account_id}"
     @options     = options.symbolize_keys
 
+    render_payload!
     publish!
   rescue ActiveRecord::RecordNotFound
     true
@@ -17,14 +18,14 @@ class PushUpdateWorker
 
   private
 
-  def payload
-    InlineRenderer.render(@status, @account, :status)
+  def render_payload!
+    @payload = StatusCacheHydrator.new(@status).hydrate(@account_id)
   end
 
   def message
     Oj.dump(
       event: update? ? :'status.update' : :update,
-      payload: payload,
+      payload: @payload,
       queued_at: (Time.now.to_f * 1000.0).to_i
     )
   end

spec/lib/status_cache_hydrator_spec.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe StatusCacheHydrator do
+  let(:status)  { Fabricate(:status) }
+  let(:account) { Fabricate(:account) }
+
+  describe '#hydrate' do
+    subject { described_class.new(status).hydrate(account.id) }
+
+    let(:compare_to_hash) { InlineRenderer.render(status, account, :status) }
+
+    context 'when cache is warm' do
+      before do
+        Rails.cache.write("fan-out/#{status.id}", InlineRenderer.render(status, nil, :status))
+      end
+
+      it 'renders the same attributes as a full render' do
+        expect(subject).to include(compare_to_hash)
+      end
+    end
+
+    context 'when cache is cold' do
+      before do
+        Rails.cache.delete("fan-out/#{status.id}")
+      end
+
+      it 'renders the same attributes as a full render' do
+        expect(subject).to include(compare_to_hash)
+      end
+    end
+
+    context 'when account has favourited status' do
+      before do
+        FavouriteService.new.call(account, status)
+      end
+
+      it 'renders the same attributes as a full render' do
+        expect(subject).to include(compare_to_hash)
+      end
+    end
+
+    context 'when account has reblogged status' do
+      before do
+        ReblogService.new.call(account, status)
+      end
+
+      it 'renders the same attributes as a full render' do
+        expect(subject).to include(compare_to_hash)
+      end
+    end
+  end
+end