Cache the number of forks of a projectforks-count-cache

The number of forks of a project doesn't change very frequently and
running a COUNT(*) every time this information is requested can be quite
expensive. We also end up running such a COUNT(*) query at least twice
on the homepage of a project.

By caching this data and refreshing it when necessary we can reduce
project homepage loading times by around 60 milliseconds (based on the
timings of https://gitlab.com/gitlab-org/gitlab-ce).

6 files changed, 84 insertions, 0 deletions

diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index d9ab44dc49f..eba71ba2f72 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -2310,4 +2310,14 @@ describe Project do
       end
     end
   end
+
+  describe '#forks_count' do
+    it 'returns the number of forks' do
+      project = build(:project)
+
+      allow(project.forks).to receive(:count).and_return(1)
+
+      expect(project.forks_count).to eq(1)
+    end
+  end
 end
diff --git a/spec/requests/api/projects_spec.rb b/spec/requests/api/projects_spec.rb
index 6cb27d16fe5..a89a58ff713 100644
--- a/spec/requests/api/projects_spec.rb
+++ b/spec/requests/api/projects_spec.rb
@@ -1065,6 +1065,14 @@ describe API::Projects do
         expect(project_fork_target.forked?).to be_truthy
       end
 
+      it 'refreshes the forks count cachce' do
+        expect(project_fork_source.forks_count).to be_zero
+
+        post api("/projects/#{project_fork_target.id}/fork/#{project_fork_source.id}", admin)
+
+        expect(project_fork_source.forks_count).to eq(1)
+      end
+
       it 'fails if forked_from project which does not exist' do
         post api("/projects/#{project_fork_target.id}/fork/9999", admin)
         expect(response).to have_http_status(404)
diff --git a/spec/requests/api/v3/projects_spec.rb b/spec/requests/api/v3/projects_spec.rb
index fca5b5b5d82..a514166274a 100644
--- a/spec/requests/api/v3/projects_spec.rb
+++ b/spec/requests/api/v3/projects_spec.rb
@@ -1004,6 +1004,14 @@ describe API::V3::Projects do
         expect(project_fork_target.forked?).to be_truthy
       end
 
+      it 'refreshes the forks count cachce' do
+        expect(project_fork_source.forks_count).to be_zero
+
+        post v3_api("/projects/#{project_fork_target.id}/fork/#{project_fork_source.id}", admin)
+
+        expect(project_fork_source.forks_count).to eq(1)
+      end
+
       it 'fails if forked_from project which does not exist' do
         post v3_api("/projects/#{project_fork_target.id}/fork/9999", admin)
         expect(response).to have_http_status(404)
diff --git a/spec/services/projects/fork_service_spec.rb b/spec/services/projects/fork_service_spec.rb
index c90536ba346..21c4b30734c 100644
--- a/spec/services/projects/fork_service_spec.rb
+++ b/spec/services/projects/fork_service_spec.rb
@@ -50,6 +50,14 @@ describe Projects::ForkService do
 
           expect(@from_project.avatar.file).to be_exists
         end
+
+        it 'flushes the forks count cache of the source project' do
+          expect(@from_project.forks_count).to be_zero
+
+          fork_project(@from_project, @to_user)
+
+          expect(@from_project.forks_count).to eq(1)
+        end
       end
     end
 
diff --git a/spec/services/projects/forks_count_service_spec.rb b/spec/services/projects/forks_count_service_spec.rb
new file mode 100644
index 00000000000..cf299c5d09b
--- /dev/null
+++ b/spec/services/projects/forks_count_service_spec.rb
@@ -0,0 +1,40 @@
+require 'spec_helper'
+
+describe Projects::ForksCountService do
+  let(:project) { build(:project, id: 42) }
+  let(:service) { described_class.new(project) }
+
+  describe '#count' do
+    it 'returns the number of forks' do
+      allow(service).to receive(:uncached_count).and_return(1)
+
+      expect(service.count).to eq(1)
+    end
+
+    it 'caches the forks count', :use_clean_rails_memory_store_caching do
+      expect(service).to receive(:uncached_count).once.and_return(1)
+
+      2.times { service.count }
+    end
+  end
+
+  describe '#refresh_cache', :use_clean_rails_memory_store_caching do
+    it 'refreshes the cache' do
+      expect(service).to receive(:uncached_count).once.and_return(1)
+
+      service.refresh_cache
+
+      expect(service.count).to eq(1)
+    end
+  end
+
+  describe '#delete_cache', :use_clean_rails_memory_store_caching do
+    it 'removes the cache' do
+      expect(service).to receive(:uncached_count).twice.and_return(1)
+
+      service.count
+      service.delete_cache
+      service.count
+    end
+  end
+end
diff --git a/spec/services/projects/unlink_fork_service_spec.rb b/spec/services/projects/unlink_fork_service_spec.rb
index 2ae8d5f7c54..4f1ab697460 100644
--- a/spec/services/projects/unlink_fork_service_spec.rb
+++ b/spec/services/projects/unlink_fork_service_spec.rb
@@ -29,4 +29,14 @@ describe Projects::UnlinkForkService do
 
     subject.execute
   end
+
+  it 'refreshes the forks count cache of the source project' do
+    source = fork_project.forked_from_project
+
+    expect(source.forks_count).to eq(1)
+
+    subject.execute
+
+    expect(source.forks_count).to be_zero
+  end
 end