From 184807b253991bc0aed20cad038c6d6602b5dba8 Mon Sep 17 00:00:00 2001
From: Igor Drozdov <idrozdov@gitlab.com>
Date: Tue, 2 Jul 2019 17:42:58 +0300
Subject: Add cleanup migration for MR's mutliple assignees

The migration steals the remaining background jobs
of populating MRs with assignees, executes them
synchronously and then makes sure that all the
assignees are migrated
---
 changelogs/unreleased/id-clean-up-mr-assignees.yml |  5 +++++
 ...6_populate_remaining_merge_request_assignees.rb | 20 +++++++++++++++++
 .../populate_merge_request_assignees_table.rb      |  8 +++++++
 .../populate_merge_request_assignees_table_spec.rb | 26 +++++++++++++++++-----
 4 files changed, 53 insertions(+), 6 deletions(-)
 create mode 100644 changelogs/unreleased/id-clean-up-mr-assignees.yml
 create mode 100644 db/post_migrate/20190702173936_populate_remaining_merge_request_assignees.rb

diff --git a/changelogs/unreleased/id-clean-up-mr-assignees.yml b/changelogs/unreleased/id-clean-up-mr-assignees.yml
new file mode 100644
index 00000000000..7ff03c9f00b
--- /dev/null
+++ b/changelogs/unreleased/id-clean-up-mr-assignees.yml
@@ -0,0 +1,5 @@
+---
+title: Add cleanup migration for MR's multiple assignees
+merge_request: 30261
+author:
+type: changed
diff --git a/db/post_migrate/20190702173936_populate_remaining_merge_request_assignees.rb b/db/post_migrate/20190702173936_populate_remaining_merge_request_assignees.rb
new file mode 100644
index 00000000000..c435b94015d
--- /dev/null
+++ b/db/post_migrate/20190702173936_populate_remaining_merge_request_assignees.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class PopulateRemainingMergeRequestAssignees < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  BATCH_SIZE = 10_000
+  MIGRATION = 'PopulateMergeRequestAssigneesTable'
+
+  disable_ddl_transaction!
+
+  def up
+    Gitlab::BackgroundMigration.steal(MIGRATION)
+
+    Gitlab::BackgroundMigration::PopulateMergeRequestAssigneesTable.new.perform_all_sync(batch_size: BATCH_SIZE)
+  end
+end
diff --git a/lib/gitlab/background_migration/populate_merge_request_assignees_table.rb b/lib/gitlab/background_migration/populate_merge_request_assignees_table.rb
index a4c6540c61b..eb4bc0aaf28 100644
--- a/lib/gitlab/background_migration/populate_merge_request_assignees_table.rb
+++ b/lib/gitlab/background_migration/populate_merge_request_assignees_table.rb
@@ -18,6 +18,14 @@ module Gitlab
         execute("INSERT INTO merge_request_assignees (merge_request_id, user_id) #{select_sql}")
       end
 
+      def perform_all_sync(batch_size:)
+        MergeRequest.each_batch(of: batch_size) do |batch|
+          range = batch.pluck('MIN(id)', 'MAX(id)').first
+
+          perform(*range)
+        end
+      end
+
       private
 
       def merge_request_assignees_not_exists_clause
diff --git a/spec/lib/gitlab/background_migration/populate_merge_request_assignees_table_spec.rb b/spec/lib/gitlab/background_migration/populate_merge_request_assignees_table_spec.rb
index 4a81a37d341..ad4fa4fe03a 100644
--- a/spec/lib/gitlab/background_migration/populate_merge_request_assignees_table_spec.rb
+++ b/spec/lib/gitlab/background_migration/populate_merge_request_assignees_table_spec.rb
@@ -27,14 +27,19 @@ describe Gitlab::BackgroundMigration::PopulateMergeRequestAssigneesTable, :migra
     merge_requests.create(params)
   end
 
+  before do
+    create_merge_request(2, assignee_id: user.id)
+    create_merge_request(3, assignee_id: user_2.id)
+    create_merge_request(4, assignee_id: user_3.id)
+
+    # Test filtering MRs without assignees
+    create_merge_request(5, assignee_id: nil)
+    # Test filtering already migrated row
+    merge_request_assignees.create!(merge_request_id: 2, user_id: user_3.id)
+  end
+
   describe '#perform' do
     it 'creates merge_request_assignees rows according to merge_requests' do
-      create_merge_request(2, assignee_id: user.id)
-      create_merge_request(3, assignee_id: user_2.id)
-      create_merge_request(4, assignee_id: user_3.id)
-      # Test filtering already migrated row
-      merge_request_assignees.create!(merge_request_id: 2, user_id: user_3.id)
-
       subject.perform(1, 4)
 
       rows = merge_request_assignees.order(:id).map { |row| row.attributes.slice('merge_request_id', 'user_id') }
@@ -53,4 +58,13 @@ describe Gitlab::BackgroundMigration::PopulateMergeRequestAssigneesTable, :migra
       end
     end
   end
+
+  describe '#perform_all_sync' do
+    it 'executes peform for all merge requests in batches' do
+      expect(subject).to receive(:perform).with(2, 4).ordered
+      expect(subject).to receive(:perform).with(5, 5).ordered
+
+      subject.perform_all_sync(batch_size: 3)
+    end
+  end
 end
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