11 files changed, 274 insertions, 66 deletions

diff --git a/app/controllers/projects/commits_controller.rb b/app/controllers/projects/commits_controller.rb
index 28920877635..5f4afd2cdee 100644
--- a/app/controllers/projects/commits_controller.rb
+++ b/app/controllers/projects/commits_controller.rb
@@ -57,6 +57,7 @@ class Projects::CommitsController < Projects::ApplicationController
         @repository.commits(@ref, path: @path, limit: @limit, offset: @offset)
       end
 
+    @commits = @commits.with_pipeline_status
     @commits = prepare_commits_for_rendering(@commits)
   end
 end
diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 22de6680511..abe4e5245b1 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -80,7 +80,8 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   def commits
     # Get commits from repository
     # or from cache if already merged
-    @commits = prepare_commits_for_rendering(@merge_request.commits)
+    @commits =
+      prepare_commits_for_rendering(@merge_request.commits.with_pipeline_status)
 
     render json: { html: view_to_html_string('projects/merge_requests/_commits') }
   end
diff --git a/app/models/ci/pipeline.rb b/app/models/ci/pipeline.rb
index 19814864e50..c77c837ff3f 100644
--- a/app/models/ci/pipeline.rb
+++ b/app/models/ci/pipeline.rb
@@ -149,34 +149,70 @@ module Ci
       end
     end
 
-    # ref can't be HEAD or SHA, can only be branch/tag name
-    scope :latest, ->(ref = nil) do
-      max_id = unscope(:select)
-        .select("max(#{quoted_table_name}.id)")
-        .group(:ref, :sha)
-
-      if ref
-        where(ref: ref, id: max_id.where(ref: ref))
-      else
-        where(id: max_id)
-      end
-    end
     scope :internal, -> { where(source: internal_sources) }
 
+    # Returns the pipelines in descending order (= newest first), optionally
+    # limited to a number of references.
+    #
+    # ref - The name (or names) of the branch(es)/tag(s) to limit the list of
+    #       pipelines to.
+    def self.newest_first(ref = nil)
+      relation = order(id: :desc)
+
+      ref ? relation.where(ref: ref) : relation
+    end
+
     def self.latest_status(ref = nil)
-      latest(ref).status
+      newest_first(ref).pluck(:status).first
     end
 
     def self.latest_successful_for(ref)
-      success.latest(ref).order(id: :desc).first
+      newest_first(ref).success.take
     end
 
     def self.latest_successful_for_refs(refs)
-      success.latest(refs).order(id: :desc).each_with_object({}) do |pipeline, hash|
+      relation = newest_first(refs).success
+
+      relation.each_with_object({}) do |pipeline, hash|
         hash[pipeline.ref] ||= pipeline
       end
     end
 
+    # Returns a Hash containing the latest pipeline status for every given
+    # commit.
+    #
+    # The keys of this Hash are the commit SHAs, the values the statuses.
+    #
+    # commits - The list of commit SHAs to get the status for.
+    # ref - The ref to scope the data to (e.g. "master"). If the ref is not
+    #       given we simply get the latest status for the commits, regardless
+    #       of what refs their pipelines belong to.
+    def self.latest_status_per_commit(commits, ref = nil)
+      p1 = arel_table
+      p2 = arel_table.alias
+
+      # This LEFT JOIN will filter out all but the newest row for every
+      # combination of (project_id, sha) or (project_id, sha, ref) if a ref is
+      # given.
+      cond = p1[:sha].eq(p2[:sha])
+        .and(p1[:project_id].eq(p2[:project_id]))
+        .and(p1[:id].lt(p2[:id]))
+
+      cond = cond.and(p1[:ref].eq(p2[:ref])) if ref
+      join = p1.join(p2, Arel::Nodes::OuterJoin).on(cond)
+
+      relation = select(:sha, :status)
+        .where(sha: commits)
+        .where(p2[:id].eq(nil))
+        .joins(join.join_sources)
+
+      relation = relation.where(ref: ref) if ref
+
+      relation.each_with_object({}) do |row, hash|
+        hash[row[:sha]] = row[:status]
+      end
+    end
+
     def self.truncate_sha(sha)
       sha[0...8]
     end
diff --git a/app/models/commit.rb b/app/models/commit.rb
index 6dba154a6ea..a31ebe9cc87 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -80,6 +80,7 @@ class Commit
 
     @raw = raw_commit
     @project = project
+    @statuses = {}
   end
 
   def id
@@ -236,11 +237,13 @@ class Commit
   end
 
   def status(ref = nil)
-    @statuses ||= {}
-
     return @statuses[ref] if @statuses.key?(ref)
 
-    @statuses[ref] = pipelines.latest_status(ref)
+    @statuses[ref] = project.pipelines.latest_status_per_commit(id, ref)[id]
+  end
+
+  def set_status_for_ref(ref, status)
+    @statuses[ref] = status
   end
 
   def signature
diff --git a/app/models/commit_collection.rb b/app/models/commit_collection.rb
new file mode 100644
index 00000000000..dd93af9df64
--- /dev/null
+++ b/app/models/commit_collection.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+# A collection of Commit instances for a specific project and Git reference.
+class CommitCollection
+  include Enumerable
+
+  attr_reader :project, :ref, :commits
+
+  # project - The project the commits belong to.
+  # commits - The Commit instances to store.
+  # ref - The name of the ref (e.g. "master").
+  def initialize(project, commits, ref = nil)
+    @project = project
+    @commits = commits
+    @ref = ref
+  end
+
+  def each(&block)
+    commits.each(&block)
+  end
+
+  # Sets the pipeline status for every commit.
+  #
+  # Setting this status ahead of time removes the need for running a query for
+  # every commit we're displaying.
+  def with_pipeline_status
+    statuses = project.pipelines.latest_status_per_commit(map(&:id), ref)
+
+    each do |commit|
+      commit.set_status_for_ref(ref, statuses[commit.id])
+    end
+
+    self
+  end
+
+  def respond_to_missing?(message, inc_private = false)
+    commits.respond_to?(message, inc_private)
+  end
+
+  # rubocop:disable GitlabSecurity/PublicSend
+  def method_missing(message, *args, &block)
+    commits.public_send(message, *args, &block)
+  end
+end
diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index 1eda0f9cbbd..5382f5cc627 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -284,8 +284,10 @@ class MergeRequestDiff < ActiveRecord::Base
 
   def load_commits
     commits = st_commits.presence || merge_request_diff_commits
+    commits = commits.map { |commit| Commit.from_hash(commit.to_hash, project) }
 
-    commits.map { |commit| Commit.from_hash(commit.to_hash, project) }
+    CommitCollection
+      .new(merge_request.source_project, commits, merge_request.source_branch)
   end
 
   def save_diffs
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 3a89fa9264b..35ee12bdfa1 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -132,7 +132,8 @@ class Repository
 
     commits = Gitlab::Git::Commit.where(options)
     commits = Commit.decorate(commits, @project) if commits.present?
-    commits
+
+    CommitCollection.new(project, commits, ref)
   end
 
   def commits_between(from, to)
@@ -148,11 +149,14 @@ class Repository
     end
 
     raw_repository.gitaly_migrate(:commits_by_message) do |is_enabled|
-      if is_enabled
-        find_commits_by_message_by_gitaly(query, ref, path, limit, offset)
-      else
-        find_commits_by_message_by_shelling_out(query, ref, path, limit, offset)
-      end
+      commits =
+        if is_enabled
+          find_commits_by_message_by_gitaly(query, ref, path, limit, offset)
+        else
+          find_commits_by_message_by_shelling_out(query, ref, path, limit, offset)
+        end
+
+      CommitCollection.new(project, commits, ref)
     end
   end
 
diff --git a/changelogs/unreleased/ci-pipeline-status-query.yml b/changelogs/unreleased/ci-pipeline-status-query.yml
new file mode 100644
index 00000000000..a464e501418
--- /dev/null
+++ b/changelogs/unreleased/ci-pipeline-status-query.yml
@@ -0,0 +1,5 @@
+---
+title: Optimise getting the pipeline status of commits
+merge_request:
+author:
+type: performance
diff --git a/spec/models/ci/pipeline_spec.rb b/spec/models/ci/pipeline_spec.rb
index 2c9e7013b77..b89b0e555d9 100644
--- a/spec/models/ci/pipeline_spec.rb
+++ b/spec/models/ci/pipeline_spec.rb
@@ -625,38 +625,29 @@ describe Ci::Pipeline, :mailer do
 
   shared_context 'with some outdated pipelines' do
     before do
-      create_pipeline(:canceled, 'ref', 'A')
-      create_pipeline(:success, 'ref', 'A')
-      create_pipeline(:failed, 'ref', 'B')
-      create_pipeline(:skipped, 'feature', 'C')
+      create_pipeline(:canceled, 'ref', 'A', project)
+      create_pipeline(:success, 'ref', 'A', project)
+      create_pipeline(:failed, 'ref', 'B', project)
+      create_pipeline(:skipped, 'feature', 'C', project)
     end
 
-    def create_pipeline(status, ref, sha)
-      create(:ci_empty_pipeline, status: status, ref: ref, sha: sha)
+    def create_pipeline(status, ref, sha, project)
+      create(
+        :ci_empty_pipeline,
+        status: status,
+        ref: ref,
+        sha: sha,
+        project: project
+      )
     end
   end
 
-  describe '.latest' do
+  describe '.newest_first' do
     include_context 'with some outdated pipelines'
 
-    context 'when no ref is specified' do
-      let(:pipelines) { described_class.latest.all }
-
-      it 'returns the latest pipeline for the same ref and different sha' do
-        expect(pipelines.map(&:sha)).to contain_exactly('A', 'B', 'C')
-        expect(pipelines.map(&:status))
-          .to contain_exactly('success', 'failed', 'skipped')
-      end
-    end
-
-    context 'when ref is specified' do
-      let(:pipelines) { described_class.latest('ref').all }
-
-      it 'returns the latest pipeline for ref and different sha' do
-        expect(pipelines.map(&:sha)).to contain_exactly('A', 'B')
-        expect(pipelines.map(&:status))
-          .to contain_exactly('success', 'failed')
-      end
+    it 'returns the pipelines from new to old' do
+      expect(described_class.newest_first.pluck(:status))
+        .to eq(%w[skipped failed success canceled])
     end
   end
 
@@ -664,20 +655,14 @@ describe Ci::Pipeline, :mailer do
     include_context 'with some outdated pipelines'
 
     context 'when no ref is specified' do
-      let(:latest_status) { described_class.latest_status }
-
-      it 'returns the latest status for the same ref and different sha' do
-        expect(latest_status).to eq(described_class.latest.status)
-        expect(latest_status).to eq('failed')
+      it 'returns the status of the latest pipeline' do
+        expect(described_class.latest_status).to eq('skipped')
       end
     end
 
     context 'when ref is specified' do
-      let(:latest_status) { described_class.latest_status('ref') }
-
-      it 'returns the latest status for ref and different sha' do
-        expect(latest_status).to eq(described_class.latest_status('ref'))
-        expect(latest_status).to eq('failed')
+      it 'returns the status of the latest pipeline for the given ref' do
+        expect(described_class.latest_status('ref')).to eq('failed')
       end
     end
   end
@@ -686,7 +671,7 @@ describe Ci::Pipeline, :mailer do
     include_context 'with some outdated pipelines'
 
     let!(:latest_successful_pipeline) do
-      create_pipeline(:success, 'ref', 'D')
+      create_pipeline(:success, 'ref', 'D', project)
     end
 
     it 'returns the latest successful pipeline' do
@@ -698,8 +683,13 @@ describe Ci::Pipeline, :mailer do
   describe '.latest_successful_for_refs' do
     include_context 'with some outdated pipelines'
 
-    let!(:latest_successful_pipeline1) { create_pipeline(:success, 'ref1', 'D') }
-    let!(:latest_successful_pipeline2) { create_pipeline(:success, 'ref2', 'D') }
+    let!(:latest_successful_pipeline1) do
+      create_pipeline(:success, 'ref1', 'D', project)
+    end
+
+    let!(:latest_successful_pipeline2) do
+      create_pipeline(:success, 'ref2', 'D', project)
+    end
 
     it 'returns the latest successful pipeline for both refs' do
       refs = %w(ref1 ref2 ref3)
@@ -708,6 +698,62 @@ describe Ci::Pipeline, :mailer do
     end
   end
 
+  describe '.latest_status_per_commit' do
+    let(:project) { create(:project) }
+
+    before do
+      pairs = [
+        %w[success ref1 123],
+        %w[manual master 123],
+        %w[failed ref 456]
+      ]
+
+      pairs.each do |(status, ref, sha)|
+        create(
+          :ci_empty_pipeline,
+          status: status,
+          ref: ref,
+          sha: sha,
+          project: project
+        )
+      end
+    end
+
+    context 'without a ref' do
+      it 'returns a Hash containing the latest status per commit for all refs' do
+        expect(described_class.latest_status_per_commit(%w[123 456]))
+          .to eq({ '123' => 'manual', '456' => 'failed' })
+      end
+
+      it 'only includes the status of the given commit SHAs' do
+        expect(described_class.latest_status_per_commit(%w[123]))
+          .to eq({ '123' => 'manual' })
+      end
+
+      context 'when there are two pipelines for a ref and SHA' do
+        it 'returns the status of the latest pipeline' do
+          create(
+            :ci_empty_pipeline,
+            status: 'failed',
+            ref: 'master',
+            sha: '123',
+            project: project
+          )
+
+          expect(described_class.latest_status_per_commit(%w[123]))
+            .to eq({ '123' => 'failed' })
+        end
+      end
+    end
+
+    context 'with a ref' do
+      it 'only includes the pipelines for the given ref' do
+        expect(described_class.latest_status_per_commit(%w[123 456], 'master'))
+          .to eq({ '123' => 'manual' })
+      end
+    end
+  end
+
   describe '.internal_sources' do
     subject { described_class.internal_sources }
 
diff --git a/spec/models/commit_collection_spec.rb b/spec/models/commit_collection_spec.rb
new file mode 100644
index 00000000000..066fe7d154e
--- /dev/null
+++ b/spec/models/commit_collection_spec.rb
@@ -0,0 +1,59 @@
+require 'spec_helper'
+
+describe CommitCollection do
+  let(:project) { create(:project, :repository) }
+  let(:commit) { project.commit }
+
+  describe '#each' do
+    it 'yields every commit' do
+      collection = described_class.new(project, [commit])
+
+      expect { |b| collection.each(&b) }.to yield_with_args(commit)
+    end
+  end
+
+  describe '#with_pipeline_status' do
+    it 'sets the pipeline status for every commit so no additional queries are necessary' do
+      create(
+        :ci_empty_pipeline,
+        ref: 'master',
+        sha: commit.id,
+        status: 'success',
+        project: project
+      )
+
+      collection = described_class.new(project, [commit])
+      collection.with_pipeline_status
+
+      recorder = ActiveRecord::QueryRecorder.new do
+        expect(commit.status).to eq('success')
+      end
+
+      expect(recorder.count).to be_zero
+    end
+  end
+
+  describe '#respond_to_missing?' do
+    it 'returns true when the underlying Array responds to the message' do
+      collection = described_class.new(project, [])
+
+      expect(collection.respond_to?(:last)).to eq(true)
+    end
+
+    it 'returns false when the underlying Array does not respond to the message' do
+      collection = described_class.new(project, [])
+
+      expect(collection.respond_to?(:foo)).to eq(false)
+    end
+  end
+
+  describe '#method_missing' do
+    it 'delegates undefined methods to the underlying Array' do
+      collection = described_class.new(project, [commit])
+
+      expect(collection.length).to eq(1)
+      expect(collection.last).to eq(commit)
+      expect(collection).not_to be_empty
+    end
+  end
+end
diff --git a/spec/models/commit_spec.rb b/spec/models/commit_spec.rb
index e3cfa149e3a..d18a5c9dfa6 100644
--- a/spec/models/commit_spec.rb
+++ b/spec/models/commit_spec.rb
@@ -351,12 +351,19 @@ eos
       end
 
       it 'gives compound status from latest pipelines if ref is nil' do
-        expect(commit.status(nil)).to eq(Ci::Pipeline.latest_status)
-        expect(commit.status(nil)).to eq('failed')
+        expect(commit.status(nil)).to eq(pipeline_from_fix.status)
       end
     end
   end
 
+  describe '#set_status_for_ref' do
+    it 'sets the status for a given reference' do
+      commit.set_status_for_ref('master', 'failed')
+
+      expect(commit.status('master')).to eq('failed')
+    end
+  end
+
   describe '#participants' do
     let(:user1) { build(:user) }
     let(:user2) { build(:user) }