Cache the number of open issues and merge requestscache-issue-and-mr-counts

Every project page displays a navigation menu that in turn displays the
number of open issues and merge requests. This means that for every
project page we run two COUNT(*) queries, each taking up roughly 30
milliseconds on GitLab.com. By caching these numbers and refreshing them
whenever necessary we can reduce loading times of all these pages by up
to roughly 60 milliseconds.

The number of open issues _includes_ confidential issues, even if you
can not see these issues. This is a trade-off to keep the code simple
and to ensure refreshing the data only needs 2 COUNT(*) queries instead
of 3. Further, by including all issues we don't need any additional work
to determine if the issue counter we display to a user should include
confidential issues or not. This does mean that if a project has 10
issues of which 5 are confidential, everybody (that can see the project)
will see the number 10.

Because we now have 3 similar counting service classes the code
previously used in Projects::ForksCountService has mostly been moved to
Projects::CountService, which in turn is reused by the various service
classes.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/36622

3 files changed, 15 insertions, 1 deletions

diff --git a/app/models/issue.rb b/app/models/issue.rb
index 1c948c8957e..9dbc018ed3e 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -54,6 +54,7 @@ class Issue < ActiveRecord::Base
   scope :preload_associations, -> { preload(:labels, project: :namespace) }
 
   after_save :expire_etag_cache
+  after_commit :update_project_counter_caches, on: :destroy
 
   attr_spammable :title, spam_title: true
   attr_spammable :description, spam_description: true
@@ -269,6 +270,10 @@ class Issue < ActiveRecord::Base
     end
   end
 
+  def update_project_counter_caches
+    Projects::OpenIssuesCountService.new(project).refresh_cache
+  end
+
   private
 
   # Returns `true` if the given User can read the current Issue.
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index ac08dc0ee1f..7fe7df75944 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -32,6 +32,7 @@ class MergeRequest < ActiveRecord::Base
 
   after_create :ensure_merge_request_diff, unless: :importing?
   after_update :reload_diff_if_branch_changed
+  after_commit :update_project_counter_caches, on: :destroy
 
   # When this attribute is true some MR validation is ignored
   # It allows us to close or modify broken merge requests
@@ -937,6 +938,10 @@ class MergeRequest < ActiveRecord::Base
     true
   end
 
+  def update_project_counter_caches
+    Projects::OpenMergeRequestsCountService.new(target_project).refresh_cache
+  end
+
   private
 
   def write_ref
diff --git a/app/models/project.rb b/app/models/project.rb
index be248bc99e1..ddef8b82dee 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -1158,7 +1158,11 @@ class Project < ActiveRecord::Base
   end
 
   def open_issues_count
-    issues.opened.count
+    Projects::OpenIssuesCountService.new(self).count
+  end
+
+  def open_merge_requests_count
+    Projects::OpenMergeRequestsCountService.new(self).count
   end
 
   def visibility_level_allowed_as_fork?(level = self.visibility_level)