Batchload blobs for diff generation

After installing a new gem, batch-loader, a construct can be used to
queue data to be fetched in bulk. The gem was also introduced in both
gitlab-org/gitlab-ce!14680 and gitlab-org/gitlab-ce!14846, but those mrs
are not merged yet.

For the generation of diffs, both the old blob and the new blob need to
be loaded. This for every file in the diff, too. Now we collect all
these so we do 1 fetch. Three `.allow_n_plus_1_calls` have been removed,
which I expect to be valid, but this needs to be confirmed by a full CI
run.

Possibly closes:
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37445
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37599
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37431

18 files changed, 86 insertions, 56 deletions

diff --git a/Gemfile b/Gemfile
index 5630f91c054..6034323956c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -263,6 +263,8 @@ gem 'gettext_i18n_rails', '~> 1.8.0'
 gem 'gettext_i18n_rails_js', '~> 1.2.0'
 gem 'gettext', '~> 3.2.2', require: false, group: :development
 
+gem 'batch-loader'
+
 # Perf bar
 gem 'peek', '~> 1.0.1'
 gem 'peek-gc', '~> 0.0.2'
diff --git a/Gemfile.lock b/Gemfile.lock
index 8f6ffa58e5d..4787be92365 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -73,6 +73,7 @@ GEM
       thread_safe (~> 0.3, >= 0.3.1)
     babosa (1.0.2)
     base32 (0.3.2)
+    batch-loader (1.1.1)
     bcrypt (3.1.11)
     bcrypt_pbkdf (1.0.0)
     benchmark-ips (2.3.0)
@@ -982,6 +983,7 @@ DEPENDENCIES
   awesome_print (~> 1.2.0)
   babosa (~> 1.0.2)
   base32 (~> 0.3.0)
+  batch-loader
   bcrypt_pbkdf (~> 1.0)
   benchmark-ips (~> 2.3.0)
   better_errors (~> 2.1.0)
diff --git a/app/controllers/projects/commit_controller.rb b/app/controllers/projects/commit_controller.rb
index 494d412b532..6ff96a3f295 100644
--- a/app/controllers/projects/commit_controller.rb
+++ b/app/controllers/projects/commit_controller.rb
@@ -22,12 +22,7 @@ class Projects::CommitController < Projects::ApplicationController
     apply_diff_view_cookie!
 
     respond_to do |format|
-      format.html do
-        # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37599
-        Gitlab::GitalyClient.allow_n_plus_1_calls do
-          render
-        end
-      end
+      format.html  { render }
       format.diff  { render text: @commit.to_diff }
       format.patch { render text: @commit.to_patch }
     end
@@ -112,7 +107,7 @@ class Projects::CommitController < Projects::ApplicationController
   end
 
   def commit
-    @noteable = @commit ||= @project.commit(params[:id])
+    @noteable = @commit ||= @project.commit_by(oid: params[:id])
   end
 
   def define_commit_vars
diff --git a/app/controllers/projects/merge_requests/diffs_controller.rb b/app/controllers/projects/merge_requests/diffs_controller.rb
index 7d16e77ef66..d60a24d3f1d 100644
--- a/app/controllers/projects/merge_requests/diffs_controller.rb
+++ b/app/controllers/projects/merge_requests/diffs_controller.rb
@@ -10,10 +10,7 @@ class Projects::MergeRequests::DiffsController < Projects::MergeRequests::Applic
   def show
     @environment = @merge_request.environments_for(current_user).last
 
-    # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37431
-    Gitlab::GitalyClient.allow_n_plus_1_calls do
-      render json: { html: view_to_html_string("projects/merge_requests/diffs/_diffs") }
-    end
+    render json: { html: view_to_html_string("projects/merge_requests/diffs/_diffs") }
   end
 
   def diff_for_path
diff --git a/app/models/blob.rb b/app/models/blob.rb
index ad0bc2e2ead..29e762724e3 100644
--- a/app/models/blob.rb
+++ b/app/models/blob.rb
@@ -76,12 +76,24 @@ class Blob < SimpleDelegator
     new(blob, project)
   end
 
+  def self.lazy(project, commit_id, path)
+    BatchLoader.for(commit_id: commit_id, path: path).batch do |items, loader|
+      project.repository.blobs_at(items.map(&:values)).each do |blob|
+        loader.call({ commit_id: blob.commit_id, path: blob.path }, blob) if blob
+      end
+    end
+  end
+
   def initialize(blob, project = nil)
     @project = project
 
     super(blob)
   end
 
+  def inspect
+    "#<#{self.class.name} oid:#{id[0..8]} commit:#{commit_id[0..8]} path:#{path}>"
+  end
+
   # Returns the data of the blob.
   #
   # If the blob is a text based blob the content is converted to UTF-8 and any
@@ -95,7 +107,10 @@ class Blob < SimpleDelegator
   end
 
   def load_all_data!
-    super(project.repository) if project
+    # Endpoint needed: gitlab-org/gitaly#756
+    Gitlab::GitalyClient.allow_n_plus_1_calls do
+      super(project.repository) if project
+    end
   end
 
   def no_highlighting?
diff --git a/app/models/commit.rb b/app/models/commit.rb
index a31ebe9cc87..8401d99a08f 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -84,7 +84,7 @@ class Commit
   end
 
   def id
-    @raw.id
+    raw.id
   end
 
   def ==(other)
@@ -361,7 +361,7 @@ class Commit
     @deltas ||= raw.deltas
   end
 
-  def diffs(diff_options = nil)
+  def diffs(diff_options = {})
     Gitlab::Diff::FileCollection::Commit.new(self, diff_options: diff_options)
   end
 
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 8a6a8377de9..26d1bc12232 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -478,6 +478,11 @@ class Repository
     nil
   end
 
+  # items is an Array like: [[oid, path], [oid1, path1]]
+  def blobs_at(items)
+    raw_repository.batch_blobs(items).map { |blob| Blob.decorate(blob, project) }
+  end
+
   def root_ref
     if raw_repository
       raw_repository.root_ref
diff --git a/changelogs/unreleased/zj-commit-show-n-1.yml b/changelogs/unreleased/zj-commit-show-n-1.yml
new file mode 100644
index 00000000000..e536434f74a
--- /dev/null
+++ b/changelogs/unreleased/zj-commit-show-n-1.yml
@@ -0,0 +1,5 @@
+---
+title: Fetch blobs in bulk when generating diffs
+merge_request:
+author:
+type: performance
diff --git a/config/initializers/batch_loader.rb b/config/initializers/batch_loader.rb
new file mode 100644
index 00000000000..2e2256b0eb9
--- /dev/null
+++ b/config/initializers/batch_loader.rb
@@ -0,0 +1 @@
+Rails.application.config.middleware.use(BatchLoader::Middleware)
diff --git a/lib/gitlab/diff/file.rb b/lib/gitlab/diff/file.rb
index ea5891a028a..d0cfe2386ca 100644
--- a/lib/gitlab/diff/file.rb
+++ b/lib/gitlab/diff/file.rb
@@ -25,6 +25,10 @@ module Gitlab
         @repository = repository
         @diff_refs = diff_refs
         @fallback_diff_refs = fallback_diff_refs
+
+        # Ensure items are collected in the the batch
+        new_blob
+        old_blob
       end
 
       def position(position_marker, position_type: :text)
@@ -95,21 +99,15 @@ module Gitlab
       end
 
       def new_blob
-        return @new_blob if defined?(@new_blob)
-
-        sha = new_content_sha
-        return @new_blob = nil unless sha
+        return unless new_content_sha
 
-        @new_blob = repository.blob_at(sha, file_path)
+        Blob.lazy(repository.project, new_content_sha, file_path)
       end
 
       def old_blob
-        return @old_blob if defined?(@old_blob)
-
-        sha = old_content_sha
-        return @old_blob = nil unless sha
+        return unless old_content_sha
 
-        @old_blob = repository.blob_at(sha, old_path)
+        Blob.lazy(repository.project, old_content_sha, old_path)
       end
 
       def content_sha
diff --git a/lib/gitlab/diff/file_collection/base.rb b/lib/gitlab/diff/file_collection/base.rb
index 88ae65cb468..a6007ebf531 100644
--- a/lib/gitlab/diff/file_collection/base.rb
+++ b/lib/gitlab/diff/file_collection/base.rb
@@ -22,10 +22,7 @@ module Gitlab
         end
 
         def diff_files
-          # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37445
-          Gitlab::GitalyClient.allow_n_plus_1_calls do
-            @diff_files ||= @diffs.decorate! { |diff| decorate_diff!(diff) }
-          end
+          @diff_files ||= @diffs.decorate! { |diff| decorate_diff!(diff) }
         end
 
         def diff_file_with_old_path(old_path)
diff --git a/lib/gitlab/git/blob.rb b/lib/gitlab/git/blob.rb
index bd5039fb87e..ddd52136bc4 100644
--- a/lib/gitlab/git/blob.rb
+++ b/lib/gitlab/git/blob.rb
@@ -179,6 +179,8 @@ module Gitlab
               )
             end
           end
+        rescue Rugged::ReferenceError
+          nil
         end
 
         def rugged_raw(repository, sha, limit:)
diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index 0c522deb6fa..3cb9b254e6e 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -1161,6 +1161,11 @@ module Gitlab
         Gitlab::Git::Blob.find(self, sha, path) unless Gitlab::Git.blank_ref?(sha)
       end
 
+      # Items should be of format [[commit_id, path], [commit_id1, path1]]
+      def batch_blobs(items, blob_size_limit: nil)
+        Gitlab::Git::Blob.batch(self, items, blob_size_limit: blob_size_limit)
+      end
+
       def commit_index(user, branch_name, index, options)
         committer = user_to_committer(user)
 
diff --git a/spec/controllers/projects/commit_controller_spec.rb b/spec/controllers/projects/commit_controller_spec.rb
index 5dc27e2bbba..fd90c0d8bad 100644
--- a/spec/controllers/projects/commit_controller_spec.rb
+++ b/spec/controllers/projects/commit_controller_spec.rb
@@ -1,15 +1,15 @@
 require 'spec_helper'
 
 describe Projects::CommitController do
-  let(:project)  { create(:project, :repository) }
-  let(:user)     { create(:user) }
+  set(:project)  { create(:project, :repository) }
+  set(:user)     { create(:user) }
   let(:commit)   { project.commit("master") }
   let(:master_pickable_sha) { '7d3b0f7cff5f37573aea97cebfd5692ea1689924' }
   let(:master_pickable_commit)  { project.commit(master_pickable_sha) }
 
   before do
     sign_in(user)
-    project.team << [user, :master]
+    project.add_master(user)
   end
 
   describe 'GET show' do
diff --git a/spec/lib/gitlab/diff/file_spec.rb b/spec/lib/gitlab/diff/file_spec.rb
index c91895cedc3..ff9acfd08b9 100644
--- a/spec/lib/gitlab/diff/file_spec.rb
+++ b/spec/lib/gitlab/diff/file_spec.rb
@@ -116,12 +116,8 @@ describe Gitlab::Diff::File do
     end
 
     context 'when renamed' do
-      let(:commit) { project.commit('6907208d755b60ebeacb2e9dfea74c92c3449a1f') }
-      let(:diff_file) { commit.diffs.diff_file_with_new_path('files/js/commit.coffee') }
-
-      before do
-        allow(diff_file.new_blob).to receive(:id).and_return(diff_file.old_blob.id)
-      end
+      let(:commit) { project.commit('94bb47ca1297b7b3731ff2a36923640991e9236f') }
+      let(:diff_file) { commit.diffs.diff_file_with_new_path('CHANGELOG.md') }
 
       it 'returns false' do
         expect(diff_file.content_changed?).to be_falsey
diff --git a/spec/models/blob_spec.rb b/spec/models/blob_spec.rb
index 47342f98283..81e35e6c931 100644
--- a/spec/models/blob_spec.rb
+++ b/spec/models/blob_spec.rb
@@ -16,6 +16,23 @@ describe Blob do
     end
   end
 
+  describe '.lazy' do
+    let(:project) { create(:project, :repository) }
+    let(:commit) { project.commit_by(oid: 'e63f41fe459e62e1228fcef60d7189127aeba95a') }
+
+    it 'fetches all blobs when the first is accessed' do
+      changelog = described_class.lazy(project, commit.id, 'CHANGELOG')
+      contributing = described_class.lazy(project, commit.id, 'CONTRIBUTING.md')
+
+      expect(Gitlab::Git::Blob).to receive(:batch).once.and_call_original
+      expect(Gitlab::Git::Blob).not_to receive(:find)
+
+      # Access property so the values are loaded
+      changelog.id
+      contributing.id
+    end
+  end
+
   describe '#data' do
     context 'using a binary blob' do
       it 'returns the data as-is' do
diff --git a/spec/models/diff_viewer/base_spec.rb b/spec/models/diff_viewer/base_spec.rb
index b26de3f3b97..c90b32c5d77 100644
--- a/spec/models/diff_viewer/base_spec.rb
+++ b/spec/models/diff_viewer/base_spec.rb
@@ -32,10 +32,8 @@ describe DiffViewer::Base do
       end
 
       context 'when the binaryness does not match' do
-        before do
-          allow(diff_file.old_blob).to receive(:binary?).and_return(false)
-          allow(diff_file.new_blob).to receive(:binary?).and_return(false)
-        end
+        let(:commit) { project.commit_by(oid: 'ae73cb07c9eeaf35924a10f713b364d32b2dd34f') }
+        let(:diff_file) { commit.diffs.diff_file_with_new_path('Gemfile.zip') }
 
         it 'returns false' do
           expect(viewer_class.can_render?(diff_file)).to be_falsey
@@ -60,8 +58,7 @@ describe DiffViewer::Base do
 
       context 'when the binaryness does not match' do
         before do
-          allow(diff_file.old_blob).to receive(:binary?).and_return(true)
-          allow(diff_file.new_blob).to receive(:binary?).and_return(true)
+          allow_any_instance_of(Blob).to receive(:binary?).and_return(true)
         end
 
         it 'returns false' do
@@ -77,12 +74,12 @@ describe DiffViewer::Base do
     end
 
     context 'when the file was renamed and only the old blob is supported' do
-      let(:commit) { project.commit('2f63565e7aac07bcdadb654e253078b727143ec4') }
+      let(:commit) { project.commit_by(oid: '2f63565e7aac07bcdadb654e253078b727143ec4') }
       let(:diff_file) { commit.diffs.diff_file_with_new_path('files/images/6049019_460s.jpg') }
 
       before do
         allow(diff_file).to receive(:renamed_file?).and_return(true)
-        allow(diff_file.new_blob).to receive(:extension).and_return('jpeg')
+        viewer_class.extensions = %w(notjpg)
       end
 
       it 'returns false' do
@@ -94,8 +91,7 @@ describe DiffViewer::Base do
   describe '#collapsed?' do
     context 'when the combined blob size is larger than the collapse limit' do
       before do
-        allow(diff_file.old_blob).to receive(:raw_size).and_return(512.kilobytes)
-        allow(diff_file.new_blob).to receive(:raw_size).and_return(513.kilobytes)
+        allow(diff_file).to receive(:raw_size).and_return(1025.kilobytes)
       end
 
       it 'returns true' do
@@ -113,8 +109,7 @@ describe DiffViewer::Base do
   describe '#too_large?' do
     context 'when the combined blob size is larger than the size limit' do
       before do
-        allow(diff_file.old_blob).to receive(:raw_size).and_return(2.megabytes)
-        allow(diff_file.new_blob).to receive(:raw_size).and_return(4.megabytes)
+        allow(diff_file).to receive(:raw_size).and_return(6.megabytes)
       end
 
       it 'returns true' do
@@ -132,8 +127,7 @@ describe DiffViewer::Base do
   describe '#render_error' do
     context 'when the combined blob size is larger than the size limit' do
       before do
-        allow(diff_file.old_blob).to receive(:raw_size).and_return(2.megabytes)
-        allow(diff_file.new_blob).to receive(:raw_size).and_return(4.megabytes)
+        allow(diff_file).to receive(:raw_size).and_return(6.megabytes)
       end
 
       it 'returns :too_large' do
diff --git a/spec/models/diff_viewer/server_side_spec.rb b/spec/models/diff_viewer/server_side_spec.rb
index 92e613f92de..98a8f6d4cc9 100644
--- a/spec/models/diff_viewer/server_side_spec.rb
+++ b/spec/models/diff_viewer/server_side_spec.rb
@@ -1,9 +1,9 @@
 require 'spec_helper'
 
 describe DiffViewer::ServerSide do
-  let(:project) { create(:project, :repository) }
-  let(:commit) { project.commit('570e7b2abdd848b95f2f578043fc23bd6f6fd24d') }
-  let(:diff_file) { commit.diffs.diff_file_with_new_path('files/ruby/popen.rb') }
+  set(:project) { create(:project, :repository) }
+  let(:commit) { project.commit_by(oid: '570e7b2abdd848b95f2f578043fc23bd6f6fd24d') }
+  let!(:diff_file) { commit.diffs.diff_file_with_new_path('files/ruby/popen.rb') }
 
   let(:viewer_class) do
     Class.new(DiffViewer::Base) do
@@ -15,8 +15,7 @@ describe DiffViewer::ServerSide do
 
   describe '#prepare!' do
     it 'loads all diff file data' do
-      expect(diff_file.old_blob).to receive(:load_all_data!)
-      expect(diff_file.new_blob).to receive(:load_all_data!)
+      expect(Blob).to receive(:lazy).at_least(:twice)
 
       subject.prepare!
     end