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

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'

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)

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

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

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?

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

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

changelogs/unreleased/zj-commit-show-n-1.yml

+---
+title: Fetch blobs in bulk when generating diffs
+merge_request:
+author:
+type: performance

config/initializers/batch_loader.rb

+Rails.application.config.middleware.use(BatchLoader::Middleware)

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
-        @new_blob = repository.blob_at(sha, file_path)
+        return unless new_content_sha
+        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
-        @old_blob = repository.blob_at(sha, old_path)
+        return unless old_content_sha
+        Blob.lazy(repository.project, old_content_sha, old_path)
       end
       def content_sha

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)

lib/gitlab/git/blob.rb

@@ -179,6 +179,8 @@ module Gitlab
               )
             end
           end
+        rescue Rugged::ReferenceError
+          nil
         end
         def rugged_raw(repository, sha, limit:)

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)

spec/controllers/projects/commit_controller_spec.rb

 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

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

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

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

spec/models/diff_viewer/server_side_spec.rb

 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