Merge branch 'gh-importer-transactions' into 'master'

Perform pull request IO work outside a transaction

See merge request gitlab-org/gitlab-ce!19372

changelogs/unreleased/gh-importer-transactions.yml

+---
+title: Move PR IO operations out of a transaction
+merge_request:
+author:
+type: performance

lib/gitlab/github_import/importer/pull_request_importer.rb

@@ -22,15 +22,22 @@ module Gitlab
         end
 
         def execute
-          if (mr_id = create_merge_request)
-            issuable_finder.cache_database_id(mr_id)
+          mr, already_exists = create_merge_request
+
+          if mr
+            insert_git_data(mr, already_exists)
+            issuable_finder.cache_database_id(mr.id)
           end
         end
 
         # Creates the merge request and returns its ID.
         #
         # This method will return `nil` if the merge request could not be
-        # created.
+        # created, otherwise it will return an Array containing the following
+        # values:
+        #
+        # 1. A MergeRequest instance.
+        # 2. A boolean indicating if the MR already exists.
         def create_merge_request
           author_id, author_found = user_finder.author_id_for(pull_request)
 
@@ -69,21 +76,42 @@ module Gitlab
             merge_request_id = GithubImport
               .insert_and_return_id(attributes, project.merge_requests)
 
-            merge_request = project.merge_requests.find(merge_request_id)
+            [project.merge_requests.find(merge_request_id), false]
+          end
+        rescue ActiveRecord::InvalidForeignKey
+          # It's possible the project has been deleted since scheduling this
+          # job. In this case we'll just skip creating the merge request.
+          []
+        rescue ActiveRecord::RecordNotUnique
+          # It's possible we previously created the MR, but failed when updating
+          # the Git data. In this case we'll just continue working on the
+          # existing row.
+          [project.merge_requests.find_by(iid: pull_request.iid), true]
+        end
 
+        def insert_git_data(merge_request, already_exists = false)
           # These fields are set so we can create the correct merge request
           # diffs.
           merge_request.source_branch_sha = pull_request.source_branch_sha
           merge_request.target_branch_sha = pull_request.target_branch_sha
 
           merge_request.keep_around_commit
-            merge_request.merge_request_diffs.create
 
-            merge_request.id
+          # MR diffs normally use an "after_save" hook to pull data from Git.
+          # All of this happens in the transaction started by calling
+          # create/save/etc. This in turn can lead to these transactions being
+          # held open for much longer than necessary. To work around this we
+          # first save the diff, then populate it.
+          diff =
+            if already_exists
+              merge_request.merge_request_diffs.take
+            else
+              merge_request.merge_request_diffs.build
             end
-        rescue ActiveRecord::InvalidForeignKey
-          # It's possible the project has been deleted since scheduling this
-          # job. In this case we'll just skip creating the merge request.
+
+          diff.importing = true
+          diff.save
+          diff.save_git_content
         end
       end
     end

spec/lib/gitlab/github_import/importer/issue_importer_spec.rb

@@ -180,12 +180,12 @@ describe Gitlab::GithubImport::Importer::IssueImporter, :clean_gitlab_redis_cach
 
       allow(importer.user_finder)
         .to receive(:user_id_for)
-        .ordered.with(issue.assignees[0])
+        .with(issue.assignees[0])
         .and_return(4)
 
       allow(importer.user_finder)
         .to receive(:user_id_for)
-        .ordered.with(issue.assignees[1])
+        .with(issue.assignees[1])
         .and_return(5)
 
       expect(Gitlab::Database)

spec/lib/gitlab/github_import/importer/pull_request_importer_spec.rb

@@ -40,13 +40,19 @@ describe Gitlab::GithubImport::Importer::PullRequestImporter, :clean_gitlab_redi
 
   describe '#execute' do
     it 'imports the pull request' do
+      mr = double(:merge_request, id: 10)
+
       expect(importer)
         .to receive(:create_merge_request)
-        .and_return(10)
+        .and_return([mr, false])
+
+      expect(importer)
+        .to receive(:insert_git_data)
+        .with(mr, false)
 
       expect_any_instance_of(Gitlab::GithubImport::IssuableFinder)
         .to receive(:cache_database_id)
-        .with(10)
+        .with(mr.id)
 
       importer.execute
     end
@@ -99,18 +105,11 @@ describe Gitlab::GithubImport::Importer::PullRequestImporter, :clean_gitlab_redi
         importer.create_merge_request
       end
 
-      it 'returns the ID of the created merge request' do
-        id = importer.create_merge_request
-
-        expect(id).to be_a_kind_of(Numeric)
-      end
-
-      it 'creates the merge request diffs' do
-        importer.create_merge_request
-
-        mr = project.merge_requests.take
+      it 'returns the created merge request' do
+        mr, exists = importer.create_merge_request
 
-        expect(mr.merge_request_diffs.exists?).to eq(true)
+        expect(mr).to be_instance_of(MergeRequest)
+        expect(exists).to eq(false)
       end
     end
 
@@ -217,5 +216,65 @@ describe Gitlab::GithubImport::Importer::PullRequestImporter, :clean_gitlab_redi
         expect { importer.create_merge_request }.not_to raise_error
       end
     end
+
+    context 'when the merge request already exists' do
+      before do
+        allow(importer.user_finder)
+          .to receive(:author_id_for)
+          .with(pull_request)
+          .and_return([user.id, true])
+
+        allow(importer.user_finder)
+          .to receive(:assignee_id_for)
+          .with(pull_request)
+          .and_return(user.id)
+      end
+
+      it 'returns the existing merge request' do
+        mr1, exists1 = importer.create_merge_request
+        mr2, exists2 = importer.create_merge_request
+
+        expect(mr2).to eq(mr1)
+        expect(exists1).to eq(false)
+        expect(exists2).to eq(true)
+      end
+    end
+  end
+
+  describe '#insert_git_data' do
+    before do
+      allow(importer.milestone_finder)
+        .to receive(:id_for)
+        .with(pull_request)
+        .and_return(milestone.id)
+
+      allow(importer.user_finder)
+        .to receive(:author_id_for)
+        .with(pull_request)
+        .and_return([user.id, true])
+
+      allow(importer.user_finder)
+        .to receive(:assignee_id_for)
+        .with(pull_request)
+        .and_return(user.id)
+    end
+
+    it 'creates the merge request diffs' do
+      mr, exists = importer.create_merge_request
+
+      importer.insert_git_data(mr, exists)
+
+      expect(mr.merge_request_diffs.exists?).to eq(true)
+    end
+
+    it 'creates the merge request diff commits' do
+      mr, exists = importer.create_merge_request
+
+      importer.insert_git_data(mr, exists)
+
+      diff = mr.merge_request_diffs.take
+
+      expect(diff.merge_request_diff_commits.exists?).to eq(true)
+    end
   end
 end