Cache the number of forks of a project

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).

1 files changed, 40 insertions, 0 deletions

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