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

1 files changed, 0 insertions, 12 deletions

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