Cache the number of open issues and merge requests

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 does not include confidential 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. A downside is that if a
project only has 5 confidential issues the counter will be set to 0.

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, 16 insertions, 0 deletions

diff --git a/spec/services/issues/close_service_spec.rb b/spec/services/issues/close_service_spec.rb
index a03f68434de..171f70c32a8 100644
--- a/spec/services/issues/close_service_spec.rb
+++ b/spec/services/issues/close_service_spec.rb
@@ -42,6 +42,11 @@ describe Issues::CloseService do
       service.execute(issue)
     end
 
+    it 'refreshes the number of open issues' do
+      expect { service.execute(issue) }
+        .to change { project.open_issues_count }.from(1).to(0)
+    end
+
     it 'invalidates counter cache for assignees' do
       expect_any_instance_of(User).to receive(:invalidate_issue_cache_counts)
 
diff --git a/spec/services/issues/create_service_spec.rb b/spec/services/issues/create_service_spec.rb
index 9b2d9e79f4f..78b11cd7991 100644
--- a/spec/services/issues/create_service_spec.rb
+++ b/spec/services/issues/create_service_spec.rb
@@ -35,6 +35,10 @@ describe Issues::CreateService do
         expect(issue.due_date).to eq Date.tomorrow
       end
 
+      it 'refreshes the number of open issues' do
+        expect { issue }.to change { project.open_issues_count }.from(0).to(1)
+      end
+
       context 'when current user cannot admin issues in the project' do
         let(:guest) { create(:user) }
 
diff --git a/spec/services/issues/reopen_service_spec.rb b/spec/services/issues/reopen_service_spec.rb
index 205e9ebd237..48fc98b3b2f 100644
--- a/spec/services/issues/reopen_service_spec.rb
+++ b/spec/services/issues/reopen_service_spec.rb
@@ -34,6 +34,13 @@ describe Issues::ReopenService do
         described_class.new(project, user).execute(issue)
       end
 
+      it 'refreshes the number of opened issues' do
+        service = described_class.new(project, user)
+
+        expect { service.execute(issue) }
+          .to change { project.open_issues_count }.from(0).to(1)
+      end
+
       context 'when issue is not confidential' do
         it 'executes issue hooks' do
           expect(project).to receive(:execute_hooks).with(an_instance_of(Hash), :issue_hooks)