Remove event caching code

Flushing the events cache worked by updating a recent number of rows in
the "events" table. This has the result that on PostgreSQL a lot of dead
tuples are produced on a regular basis. This in turn means that
PostgreSQL will spend considerable amounts of time vacuuming this table.
This in turn can lead to an increase of database load.

For GitLab.com we measured the impact of not using events caching and
found no measurable increase in response timings. Meanwhile not flushing
the events cache lead to the "events" table having no more dead tuples
as now rows are only inserted into this table.

As a result of this we are hereby removing events caching as it does not
appear to help and only increases database load.

For more information see the following comment:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6578#note_18864037

6 files changed, 0 insertions, 74 deletions

diff --git a/app/models/event.rb b/app/models/event.rb
index 21eaca917b8..216dba46e74 100644
--- a/app/models/event.rb
+++ b/app/models/event.rb
@@ -43,12 +43,6 @@ class Event < ActiveRecord::Base
   scope :for_milestone_id, ->(milestone_id) { where(target_type: "Milestone", target_id: milestone_id) }
 
   class << self
-    def reset_event_cache_for(target)
-      Event.where(target_id: target.id, target_type: target.class.to_s).
-        order('id DESC').limit(100).
-        update_all(updated_at: Time.now)
-    end
-
     # Update Gitlab::ContributionsCalendar#activity_dates if this changes
     def contributions
       where("action = ? OR (target_type in (?) AND action in (?))",
diff --git a/app/models/issue.rb b/app/models/issue.rb
index 6e8f5d3c422..544f830cc69 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -182,18 +182,6 @@ class Issue < ActiveRecord::Base
     branches_with_iid - branches_with_merge_request
   end
 
-  # Reset issue events cache
-  #
-  # Since we do cache @event we need to reset cache in special cases:
-  # * when an issue is updated
-  # Events cache stored like  events/23-20130109142513.
-  # The cache key includes updated_at timestamp.
-  # Thus it will automatically generate a new fragment
-  # when the event is updated because the key changes.
-  def reset_events_cache
-    Event.reset_event_cache_for(self)
-  end
-
   # To allow polymorphism with MergeRequest.
   def source_project
     project
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 6c3c093d084..bf9edb0b823 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -601,18 +601,6 @@ class MergeRequest < ActiveRecord::Base
     self.target_project.repository.branch_names.include?(self.target_branch)
   end
 
-  # Reset merge request events cache
-  #
-  # Since we do cache @event we need to reset cache in special cases:
-  # * when a merge request is updated
-  # Events cache stored like  events/23-20130109142513.
-  # The cache key includes updated_at timestamp.
-  # Thus it will automatically generate a new fragment
-  # when the event is updated because the key changes.
-  def reset_events_cache
-    Event.reset_event_cache_for(self)
-  end
-
   def merge_commit_message
     message = "Merge branch '#{source_branch}' into '#{target_branch}'\n\n"
     message << "#{title}\n\n"
diff --git a/app/models/note.rb b/app/models/note.rb
index 9ff5e308ed2..9881506edc8 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -198,19 +198,6 @@ class Note < ActiveRecord::Base
     super(noteable_type.to_s.classify.constantize.base_class.to_s)
   end
 
-  # Reset notes events cache
-  #
-  # Since we do cache @event we need to reset cache in special cases:
-  # * when a note is updated
-  # * when a note is removed
-  # Events cache stored like  events/23-20130109142513.
-  # The cache key includes updated_at timestamp.
-  # Thus it will automatically generate a new fragment
-  # when the event is updated because the key changes.
-  def reset_events_cache
-    Event.reset_event_cache_for(self)
-  end
-
   def editable?
     !system?
   end
diff --git a/app/models/project.rb b/app/models/project.rb
index 76c1fc4945d..21d9ed0f51f 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -973,7 +973,6 @@ class Project < ActiveRecord::Base
       begin
         gitlab_shell.mv_repository(repository_storage_path, "#{old_path_with_namespace}.wiki", "#{new_path_with_namespace}.wiki")
         send_move_instructions(old_path_with_namespace)
-        reset_events_cache
 
         @old_path_with_namespace = old_path_with_namespace
 
@@ -1040,22 +1039,6 @@ class Project < ActiveRecord::Base
     attrs
   end
 
-  # Reset events cache related to this project
-  #
-  # Since we do cache @event we need to reset cache in special cases:
-  # * when project was moved
-  # * when project was renamed
-  # * when the project avatar changes
-  # Events cache stored like  events/23-20130109142513.
-  # The cache key includes updated_at timestamp.
-  # Thus it will automatically generate a new fragment
-  # when the event is updated because the key changes.
-  def reset_events_cache
-    Event.where(project_id: self.id).
-      order('id DESC').limit(100).
-      update_all(updated_at: Time.now)
-  end
-
   def project_member(user)
     project_members.find_by(user_id: user)
   end
diff --git a/app/models/user.rb b/app/models/user.rb
index 29fb849940a..8a67aa94e79 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -704,20 +704,6 @@ class User < ActiveRecord::Base
       project.project_member(self)
   end
 
-  # Reset project events cache related to this user
-  #
-  # Since we do cache @event we need to reset cache in special cases:
-  # * when the user changes their avatar
-  # Events cache stored like  events/23-20130109142513.
-  # The cache key includes updated_at timestamp.
-  # Thus it will automatically generate a new fragment
-  # when the event is updated because the key changes.
-  def reset_events_cache
-    Event.where(author_id: id).
-      order('id DESC').limit(1000).
-      update_all(updated_at: Time.now)
-  end
-
   def full_website_url
     return "http://#{website_url}" if website_url !~ /\Ahttps?:\/\//