Cache commits on the repository model

app/models/ci/pipeline.rb

@@ -249,9 +249,7 @@ module Ci
     end
 
     def commit
-      @commit ||= project.commit(sha)
-    rescue
-      nil
+      @commit ||= project.commit_by(oid: sha)
     end
 
     def branch?

app/models/project.rb

@@ -540,6 +540,10 @@ class Project < ActiveRecord::Base
     repository.commit(ref)
   end
 
+  def commit_by(oid:)
+    repository.commit_by(oid: oid)
+  end
+
   # ref can't be HEAD, can only be branch/tag name or SHA
   def latest_successful_builds_for(ref = default_branch)
     latest_pipeline = pipelines.latest_successful_for(ref)
@@ -553,7 +557,7 @@ class Project < ActiveRecord::Base
 
   def merge_base_commit(first_commit_id, second_commit_id)
     sha = repository.merge_base(first_commit_id, second_commit_id)
-    repository.commit(sha) if sha
+    commit_by(oid: sha) if sha
   end
 
   def saved?

app/models/repository.rb

@@ -76,6 +76,7 @@ class Repository
     @full_path = full_path
     @disk_path = disk_path || full_path
     @project = project
+    @commit_cache = {}
   end
 
   def ==(other)
@@ -103,18 +104,17 @@ class Repository
 
   def commit(ref = 'HEAD')
     return nil unless exists?
+    return ref if ref.is_a?(::Commit)
 
-    commit =
-      if ref.is_a?(Gitlab::Git::Commit)
-        ref
-      else
-        Gitlab::Git::Commit.find(raw_repository, ref)
-      end
+    find_commit(ref)
+  end
 
-    commit = ::Commit.new(commit, @project) if commit
-    commit
-  rescue Rugged::OdbError, Rugged::TreeError
-    nil
+  # Finding a commit by the passed SHA
+  # Also takes care of caching, based on the SHA
+  def commit_by(oid:)
+    return @commit_cache[oid] if @commit_cache.key?(oid)
+
+    @commit_cache[oid] = find_commit(oid)
   end
 
   def commits(ref, path: nil, limit: nil, offset: nil, skip_merges: false, after: nil, before: nil)
@@ -231,7 +231,7 @@ class Repository
   # branches or tags, but we want to keep some of these commits around, for
   # example if they have comments or CI builds.
   def keep_around(sha)
-    return unless sha && commit(sha)
+    return unless sha && commit_by(oid: sha)
 
     return if kept_around?(sha)
 
@@ -1069,6 +1069,18 @@ class Repository
 
   private
 
+  # TODO Generice finder, later split this on finders by Ref or Oid
+  # gitlab-org/gitlab-ce#39239
+  def find_commit(oid_or_ref)
+    commit = if oid_or_ref.is_a?(Gitlab::Git::Commit)
+               oid_or_ref
+             else
+               Gitlab::Git::Commit.find(raw_repository, oid_or_ref)
+             end
+
+    ::Commit.new(commit, @project) if commit
+  end
+
   def blob_data_at(sha, path)
     blob = blob_at(sha, path)
     return unless blob
@@ -1107,12 +1119,12 @@ class Repository
 
   def last_commit_for_path_by_gitaly(sha, path)
     c = raw_repository.gitaly_commit_client.last_commit_for_path(sha, path)
-    commit(c)
+    commit_by(oid: c)
   end
 
   def last_commit_for_path_by_rugged(sha, path)
     sha = last_commit_id_for_path_by_shelling_out(sha, path)
-    commit(sha)
+    commit_by(oid: sha)
   end
 
   def last_commit_id_for_path_by_shelling_out(sha, path)

changelogs/unreleased/zj-commit-cache.yml

+---
+title: Cache commits fetched from the repository
+merge_request:
+author:
+type: performance

lib/gitlab/git/commit.rb

@@ -72,7 +72,8 @@ module Gitlab
 
           decorate(repo, commit) if commit
         rescue Rugged::ReferenceError, Rugged::InvalidError, Rugged::ObjectError,
-               Gitlab::Git::CommandError, Gitlab::Git::Repository::NoRepository
+               Gitlab::Git::CommandError, Gitlab::Git::Repository::NoRepository,
+               Rugged::OdbError, Rugged::TreeError
           nil
         end
 

spec/controllers/projects/pipelines_controller_spec.rb

@@ -46,7 +46,7 @@ describe Projects::PipelinesController do
 
     context 'when performing gitaly calls', :request_store do
       it 'limits the Gitaly requests' do
-        expect { subject }.to change { Gitlab::GitalyClient.get_request_count }.by(10)
+        expect { subject }.to change { Gitlab::GitalyClient.get_request_count }.by(8)
       end
     end
   end

spec/models/merge_request_spec.rb

@@ -86,7 +86,7 @@ describe MergeRequest do
 
     context 'when the target branch does not exist' do
       before do
-        project.repository.raw_repository.delete_branch(subject.target_branch)
+        project.repository.rm_branch(subject.author, subject.target_branch)
       end
 
       it 'returns nil' do
@@ -1388,7 +1388,7 @@ describe MergeRequest do
 
     context 'when the target branch does not exist' do
       before do
-        subject.project.repository.raw_repository.delete_branch(subject.target_branch)
+        subject.project.repository.rm_branch(subject.author, subject.target_branch)
       end
 
       it 'returns nil' do

spec/models/repository_spec.rb

@@ -2238,4 +2238,24 @@ describe Repository do
       end
     end
   end
+
+  describe 'commit cache' do
+    set(:project) { create(:project, :repository) }
+
+    it 'caches based on SHA' do
+      # Gets the commit oid, and warms the cache
+      oid = project.commit.id
+
+      expect(Gitlab::Git::Commit).not_to receive(:find).once
+
+      project.commit_by(oid: oid)
+    end
+
+    it 'caches nil values' do
+      expect(Gitlab::Git::Commit).to receive(:find).once
+
+      project.commit_by(oid: '1' * 40)
+      project.commit_by(oid: '1' * 40)
+    end
+  end
 end