Remove lease from Event#reset_project_activity

Per GitLab.com's performance metrics this method could take up to 5
seconds of wall time to complete, while only taking 1-2 milliseconds of
CPU time. Removing the Redis lease in favour of conditional updates
allows us to work around this.

A slight drawback is that this allows for multiple threads/processes to
try and update the same row. However, only a single thread/process will
ever win since the UPDATE query uses a WHERE condition to only update
rows that were not updated in the last hour.

Fixes gitlab-org/gitlab-ce#22473

1 files changed, 7 insertions, 12 deletions

diff --git a/app/models/event.rb b/app/models/event.rb
index 55a76e26f3c..633019fe0af 100644
--- a/app/models/event.rb
+++ b/app/models/event.rb
@@ -328,13 +328,15 @@ class Event < ActiveRecord::Base
   def reset_project_activity
     return unless project
 
-    # Don't even bother obtaining a lock if the last update happened less than
-    # 60 minutes ago.
+    # Don't bother updating if we know the project was updated recently.
     return if recent_update?
 
-    return unless try_obtain_lease
-
-    project.update_column(:last_activity_at, created_at)
+    # At this point it's possible for multiple threads/processes to try to
+    # update the project. Only one query should actually perform the update,
+    # hence we add the extra WHERE clause for last_activity_at.
+    Project.unscoped.where(id: project_id).
+      where('last_activity_at > ?', RESET_PROJECT_ACTIVITY_INTERVAL.ago).
+      update_all(last_activity_at: created_at)
   end
 
   private
@@ -342,11 +344,4 @@ class Event < ActiveRecord::Base
   def recent_update?
     project.last_activity_at > RESET_PROJECT_ACTIVITY_INTERVAL.ago
   end
-
-  def try_obtain_lease
-    Gitlab::ExclusiveLease.
-      new("project:update_last_activity_at:#{project.id}",
-          timeout: RESET_PROJECT_ACTIVITY_INTERVAL.to_i).
-      try_obtain
-  end
 end