Cache commit stats for a single commit

Changelog: performance

lib/gitlab/git/commit_stats.rb

@@ -14,21 +14,23 @@ module Gitlab
       # Gitaly migration: https://gitlab.com/gitlab-org/gitaly/issues/323
       def initialize(repo, commit)
         @id = commit.id
-        @additions = 0
-        @deletions = 0
-        @total = 0
 
-        wrapped_gitaly_errors do
-          gitaly_stats(repo, commit)
-        end
-      end
+        additions, deletions = fetch_stats(repo, commit)
 
-      def gitaly_stats(repo, commit)
-        stats = repo.gitaly_commit_client.commit_stats(@id)
-        @additions = stats.additions
-        @deletions = stats.deletions
+        @additions = additions.to_i
+        @deletions = deletions.to_i
         @total = @additions + @deletions
       end
+
+      def fetch_stats(repo, commit)
+        Rails.cache.fetch("commit_stats:#{repo.gl_project_path}:#{@id}") do
+          stats = wrapped_gitaly_errors do
+            repo.gitaly_commit_client.commit_stats(@id)
+          end
+
+          [stats.additions, stats.deletions]
+        end
+      end
     end
   end
 end

spec/lib/gitlab/git/commit_stats_spec.rb

+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe Gitlab::Git::CommitStats, :seed_helper do
+  let(:repository) { Gitlab::Git::Repository.new('default', TEST_REPO_PATH, '', 'group/project') }
+  let(:commit) { Gitlab::Git::Commit.find(repository, SeedRepo::Commit::ID) }
+
+  def verify_stats!
+    stats = described_class.new(repository, commit)
+
+    expect(stats).to have_attributes(
+      additions: eq(11),
+      deletions: eq(6),
+      total: eq(17)
+    )
+  end
+
+  it 'returns commit stats and caches them', :use_clean_rails_redis_caching do
+    expect(repository.gitaly_commit_client).to receive(:commit_stats).with(commit.id).and_call_original
+
+    verify_stats!
+
+    expect(Rails.cache.fetch("commit_stats:group/project:#{commit.id}")).to eq([11, 6])
+
+    expect(repository.gitaly_commit_client).not_to receive(:commit_stats)
+
+    verify_stats!
+  end
+end