Fix #2619 - When redis feed is empty, fall back to database (#3721)

* Fix #2619 - When redis feed is empty, fall back to database

* Use redis value to return feed from database only while RegenerationWorker
hasn't finished running

* Fix specs

* Replace usage of reject!

3 files changed, 23 insertions, 3 deletions

diff --git a/app/controllers/concerns/user_tracking_concern.rb b/app/controllers/concerns/user_tracking_concern.rb
index 2a3449617..8a63af95d 100644
--- a/app/controllers/concerns/user_tracking_concern.rb
+++ b/app/controllers/concerns/user_tracking_concern.rb
@@ -17,7 +17,7 @@ module UserTrackingConcern
     current_user.update_tracked_fields!(request)
 
     # Regenerate feed if needed
-    RegenerationWorker.perform_async(current_user.account_id) if user_needs_feed_update?
+    regenerate_feed! if user_needs_feed_update?
   end
 
   def user_needs_sign_in_update?
@@ -27,4 +27,9 @@ module UserTrackingConcern
   def user_needs_feed_update?
     current_user.last_sign_in_at < REGENERATE_FEED_DAYS.days.ago
   end
+
+  def regenerate_feed!
+    Redis.current.setnx("account:#{current_user.account_id}:regeneration", true) == 1 && Redis.current.expire("account:#{current_user.account_id}:regeneration", 3_600 * 24)
+    RegenerationWorker.perform_async(current_user.account_id)
+  end
 end
diff --git a/app/models/feed.rb b/app/models/feed.rb
index 3cbc160a0..5125e51ff 100644
--- a/app/models/feed.rb
+++ b/app/models/feed.rb
@@ -7,15 +7,28 @@ class Feed
   end
 
   def get(limit, max_id = nil, since_id = nil)
+    if redis.exists("account:#{@account.id}:regeneration")
+      from_database(limit, max_id, since_id)
+    else
+      from_redis(limit, max_id, since_id)
+    end
+  end
+
+  private
+
+  def from_redis(limit, max_id, since_id)
     max_id     = '+inf' if max_id.blank?
     since_id   = '-inf' if since_id.blank?
     unhydrated = redis.zrevrangebyscore(key, "(#{max_id}", "(#{since_id}", limit: [0, limit], with_scores: true).map(&:last).map(&:to_i)
     status_map = Status.where(id: unhydrated).cache_ids.map { |s| [s.id, s] }.to_h
-
     unhydrated.map { |id| status_map[id] }.compact
   end
 
-  private
+  def from_database(limit, max_id, since_id)
+    Status.as_home_timeline(@account)
+          .paginate_by_max_id(limit, max_id, since_id)
+          .reject { |status| FeedManager.instance.filter?(:home, status, @account.id) }
+  end
 
   def key
     FeedManager.instance.key(@type, @account.id)
diff --git a/app/services/precompute_feed_service.rb b/app/services/precompute_feed_service.rb
index acda5108a..626ec2f6c 100644
--- a/app/services/precompute_feed_service.rb
+++ b/app/services/precompute_feed_service.rb
@@ -17,6 +17,8 @@ class PrecomputeFeedService < BaseService
       statuses.each do |status|
         process_status(status)
       end
+
+      redis.del("account:#{@account.id}:regeneration")
     end
   end