Batch load only data from same repository when lazy object is accessed

By specifying `key`, we get a different lazy batch loader for each
repository, which means that accessing a lazy object from one repository
will only result in that repository's objects being fetched, not those
of other repositories, saving us some unnecessary Gitaly lookups.

app/graphql/resolvers/full_path_resolver.rb

@@ -11,10 +11,11 @@ module Resolvers
     end
 
     def model_by_full_path(model, full_path)
-      BatchLoader.for(full_path).batch(key: "#{model.model_name.param_key}:full_path") do |full_paths, loader|
+      BatchLoader.for(full_path).batch(key: model) do |full_paths, loader, args|
         # `with_route` avoids an N+1 calculating full_path
-        results = model.where_full_path_in(full_paths).with_route
-        results.each { |project| loader.call(project.full_path, project) }
+        args[:key].where_full_path_in(full_paths).with_route.each do |project|
+          loader.call(project.full_path, project)
+        end
       end
     end
   end

app/graphql/resolvers/merge_request_resolver.rb

@@ -14,9 +14,10 @@ module Resolvers
     def resolve(iid:)
       return unless project.present?
 
-      BatchLoader.for(iid.to_s).batch(key: project.id) do |iids, loader|
-        results = project.merge_requests.where(iid: iids)
-        results.each { |mr| loader.call(mr.iid.to_s, mr) }
+      BatchLoader.for(iid.to_s).batch(key: project) do |iids, loader, args|
+        args[:key].merge_requests.where(iid: iids).each do |mr|
+          loader.call(mr.iid.to_s, mr)
+        end
       end
     end
     # rubocop: enable CodeReuse/ActiveRecord

app/models/blob.rb

@@ -80,15 +80,9 @@ class Blob < SimpleDelegator
   end
 
   def self.lazy(project, commit_id, path)
-    BatchLoader.for({ project: project, commit_id: commit_id, path: path }).batch do |items, loader|
-      items_by_project = items.group_by { |i| i[:project] }
-
-      items_by_project.each do |project, items|
-        items = items.map { |i| i.values_at(:commit_id, :path) }
-
-        project.repository.blobs_at(items).each do |blob|
-          loader.call({ project: blob.project, commit_id: blob.commit_id, path: blob.path }, blob) if blob
-        end
+    BatchLoader.for([commit_id, path]).batch(key: project.repository) do |items, loader, args|
+      args[:key].blobs_at(items).each do |blob|
+        loader.call([blob.commit_id, blob.path], blob) if blob
       end
     end
   end

changelogs/unreleased/dm-batch-loader-key.yml

+---
+title: Batch load only data from same repository when lazy object is accessed
+merge_request: 23309
+author:
+type: performance

lib/gitlab/git/commit.rb

@@ -155,17 +155,9 @@ module Gitlab
         end
 
         def extract_signature_lazily(repository, commit_id)
-          BatchLoader.for({ repository: repository, commit_id: commit_id }).batch do |items, loader|
-            items_by_repo = items.group_by { |i| i[:repository] }
-
-            items_by_repo.each do |repo, items|
-              commit_ids = items.map { |i| i[:commit_id] }
-
-              signatures = batch_signature_extraction(repository, commit_ids)
-
-              signatures.each do |commit_sha, signature_data|
-                loader.call({ repository: repository, commit_id: commit_sha }, signature_data)
-              end
+          BatchLoader.for(commit_id).batch(key: repository) do |commit_ids, loader, args|
+            batch_signature_extraction(args[:key], commit_ids).each do |commit_id, signature_data|
+              loader.call(commit_id, signature_data)
             end
           end
         end
@@ -175,17 +167,9 @@ module Gitlab
         end
 
         def get_message(repository, commit_id)
-          BatchLoader.for({ repository: repository, commit_id: commit_id }).batch do |items, loader|
-            items_by_repo = items.group_by { |i| i[:repository] }
-
-            items_by_repo.each do |repo, items|
-              commit_ids = items.map { |i| i[:commit_id] }
-
-              messages = get_messages(repository, commit_ids)
-
-              messages.each do |commit_sha, message|
-                loader.call({ repository: repository, commit_id: commit_sha }, message)
-              end
+          BatchLoader.for(commit_id).batch(key: repository) do |commit_ids, loader, args|
+            get_messages(args[:key], commit_ids).each do |commit_id, message|
+              loader.call(commit_id, message)
             end
           end
         end

lib/gitlab/git/tag.rb

@@ -14,17 +14,9 @@ module Gitlab
 
       class << self
         def get_message(repository, tag_id)
-          BatchLoader.for({ repository: repository, tag_id: tag_id }).batch do |items, loader|
-            items_by_repo = items.group_by { |i| i[:repository] }
-
-            items_by_repo.each do |repo, items|
-              tag_ids = items.map { |i| i[:tag_id] }
-
-              messages = get_messages(repository, tag_ids)
-
-              messages.each do |id, message|
-                loader.call({ repository: repository, tag_id: id }, message)
-              end
+          BatchLoader.for(tag_id).batch(key: repository) do |tag_ids, loader, args|
+            get_messages(args[:key], tag_ids).each do |tag_id, message|
+              loader.call(tag_id, message)
             end
           end
         end

spec/lib/gitlab/git/commit_spec.rb

@@ -450,11 +450,17 @@ describe Gitlab::Git::Commit, :seed_helper do
             described_class.extract_signature_lazily(repository, commit_id)
           end
 
+          other_repository = double(:repository)
+          described_class.extract_signature_lazily(other_repository, commit_ids.first)
+
           expect(described_class).to receive(:batch_signature_extraction)
             .with(repository, commit_ids)
             .once
             .and_return({})
 
+          expect(described_class).not_to receive(:batch_signature_extraction)
+            .with(other_repository, commit_ids.first)
+
           2.times { signatures.each(&:itself) }
         end
       end

spec/lib/gitlab/git/tag_spec.rb

@@ -38,6 +38,9 @@ describe Gitlab::Git::Tag, :seed_helper do
     end
 
     it 'gets messages in one batch', :request_store do
+      other_repository = double(:repository)
+      described_class.get_message(other_repository, tag_ids.first)
+
       expect { subject.map(&:itself) }.to change { Gitlab::GitalyClient.get_request_count }.by(1)
     end
   end

spec/models/blob_spec.rb

@@ -18,14 +18,23 @@ describe Blob do
 
   describe '.lazy' do
     let(:project) { create(:project, :repository) }
-    let(:commit) { project.commit_by(oid: 'e63f41fe459e62e1228fcef60d7189127aeba95a') }
+    let(:other_project) { create(:project, :repository) }
+    let(:commit_id) { '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')
+    it 'does not fetch blobs when none are accessed' do
+      expect(project.repository).not_to receive(:blobs_at)
 
-      expect(Gitlab::Git::Blob).to receive(:batch).once.and_call_original
-      expect(Gitlab::Git::Blob).not_to receive(:find)
+      described_class.lazy(project, commit_id, 'CHANGELOG')
+    end
+
+    it 'fetches all blobs for the same repository when one is accessed' do
+      expect(project.repository).to receive(:blobs_at).with([[commit_id, 'CHANGELOG'], [commit_id, 'CONTRIBUTING.md']]).once.and_call_original
+      expect(other_project.repository).not_to receive(:blobs_at)
+
+      changelog = described_class.lazy(project, commit_id, 'CHANGELOG')
+      contributing = described_class.lazy(project, commit_id, 'CONTRIBUTING.md')
+
+      described_class.lazy(other_project, commit_id, 'CHANGELOG')
 
       # Access property so the values are loaded
       changelog.id