Reset merge status from mergeable MRs

Adds migrations to reset the merge_status of opened,
mergeable MRs. That's required by
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28513
so we're able to sync the status update along merge-ref,
without leaving MRs with a stale merge-ref.

changelogs/unreleased/osw-reset-merge-status-from-mergeable-mrs.yml

+---
+title: Reset merge status from mergeable MRs
+merge_request: 28843
+author:
+type: other

db/migrate/20190530154715_add_index_to_merge_requests_state_and_merge_status.rb

+# 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 AddIndexToMergeRequestsStateAndMergeStatus < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :merge_requests, [:state, :merge_status],
+                         where: "state = 'opened' AND merge_status = 'can_be_merged'"
+  end
+
+  def down
+    remove_concurrent_index :merge_requests, [:state, :merge_status]
+  end
+end

db/post_migrate/20190528180441_enqueue_reset_merge_status.rb

+# 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 EnqueueResetMergeStatus < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  BATCH_SIZE = 10_000
+  MIGRATION = 'ResetMergeStatus'
+  DELAY_INTERVAL = 5.minutes.to_i
+
+  disable_ddl_transaction!
+
+  def up
+    say 'Scheduling `ResetMergeStatus` jobs'
+
+    # We currently have around 135_000 opened, mergeable MRs in GitLab.com. This iteration
+    # will schedule around 13 batches of 10_000 MRs, which should take around 1 hour to
+    # complete.
+    relation = MergeRequest.where(state: 'opened', merge_status: 'can_be_merged')
+
+    relation.each_batch(of: BATCH_SIZE) do |batch, index|
+      range = batch.pluck('MIN(id)', 'MAX(id)').first
+
+      BackgroundMigrationWorker.perform_in(index * DELAY_INTERVAL, MIGRATION, range)
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20190527194900) do
+ActiveRecord::Schema.define(version: 20190530154715) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1361,6 +1361,7 @@ ActiveRecord::Schema.define(version: 20190527194900) do
     t.index ["source_branch"], name: "index_merge_requests_on_source_branch", using: :btree
     t.index ["source_project_id", "source_branch"], name: "index_merge_requests_on_source_project_and_branch_state_opened", where: "((state)::text = 'opened'::text)", using: :btree
     t.index ["source_project_id", "source_branch"], name: "index_merge_requests_on_source_project_id_and_source_branch", using: :btree
+    t.index ["state", "merge_status"], name: "index_merge_requests_on_state_and_merge_status", where: "(((state)::text = 'opened'::text) AND ((merge_status)::text = 'can_be_merged'::text))", using: :btree
     t.index ["target_branch"], name: "index_merge_requests_on_target_branch", using: :btree
     t.index ["target_project_id", "iid"], name: "index_merge_requests_on_target_project_id_and_iid", unique: true, using: :btree
     t.index ["target_project_id", "iid"], name: "index_merge_requests_on_target_project_id_and_iid_opened", where: "((state)::text = 'opened'::text)", using: :btree

lib/gitlab/background_migration/reset_merge_status.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # Updates the range of given MRs to merge_status "unchecked", if they're opened
+    # and mergeable.
+    class ResetMergeStatus
+      def perform(from_id, to_id)
+        relation = MergeRequest.where(id: from_id..to_id,
+                                      state: 'opened',
+                                      merge_status: 'can_be_merged')
+
+        relation.update_all(merge_status: 'unchecked')
+      end
+    end
+  end
+end

spec/lib/gitlab/background_migration/reset_merge_status_spec.rb

+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe Gitlab::BackgroundMigration::ResetMergeStatus, :migration, schema: 20190528180441 do
+  let(:namespaces) { table(:namespaces) }
+  let(:projects) { table(:projects) }
+  let(:namespace) { namespaces.create(name: 'gitlab', path: 'gitlab-org') }
+  let(:project) { projects.create(namespace_id: namespace.id, name: 'foo') }
+  let(:merge_requests) { table(:merge_requests) }
+
+  def create_merge_request(id, extra_params = {})
+    params = {
+      id: id,
+      target_project_id: project.id,
+      target_branch: 'master',
+      source_project_id: project.id,
+      source_branch: 'mr name',
+      title: "mr name#{id}"
+    }.merge(extra_params)
+
+    merge_requests.create!(params)
+  end
+
+  it 'correctly updates opened mergeable MRs to unchecked' do
+    create_merge_request(1, state: 'opened', merge_status: 'can_be_merged')
+    create_merge_request(2, state: 'opened', merge_status: 'can_be_merged')
+    create_merge_request(3, state: 'opened', merge_status: 'can_be_merged')
+    create_merge_request(4, state: 'merged', merge_status: 'can_be_merged')
+    create_merge_request(5, state: 'opened', merge_status: 'cannot_be_merged')
+
+    subject.perform(1, 5)
+
+    expected_rows = [
+      { id: 1, state: 'opened', merge_status: 'unchecked' },
+      { id: 2, state: 'opened', merge_status: 'unchecked' },
+      { id: 3, state: 'opened', merge_status: 'unchecked' },
+      { id: 4, state: 'merged', merge_status: 'can_be_merged' },
+      { id: 5, state: 'opened', merge_status: 'cannot_be_merged' }
+    ]
+
+    rows = merge_requests.order(:id).map do |row|
+      row.attributes.slice('id', 'state', 'merge_status').symbolize_keys
+    end
+
+    expect(rows).to eq(expected_rows)
+  end
+end

spec/migrations/enqueue_reset_merge_status_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20190528180441_enqueue_reset_merge_status.rb')
+
+describe EnqueueResetMergeStatus, :migration, :sidekiq do
+  let(:namespaces) { table(:namespaces) }
+  let(:projects) { table(:projects) }
+  let(:namespace) { namespaces.create(name: 'gitlab', path: 'gitlab-org') }
+  let(:project) { projects.create(namespace_id: namespace.id, name: 'foo') }
+  let(:merge_requests) { table(:merge_requests) }
+
+  def create_merge_request(id, extra_params = {})
+    params = {
+      id: id,
+      target_project_id: project.id,
+      target_branch: 'master',
+      source_project_id: project.id,
+      source_branch: 'mr name',
+      title: "mr name#{id}"
+    }.merge(extra_params)
+
+    merge_requests.create!(params)
+  end
+
+  it 'correctly schedules background migrations' do
+    create_merge_request(1, state: 'opened', merge_status: 'can_be_merged')
+    create_merge_request(2, state: 'opened', merge_status: 'can_be_merged')
+    create_merge_request(3, state: 'opened', merge_status: 'can_be_merged')
+    create_merge_request(4, state: 'merged', merge_status: 'can_be_merged')
+    create_merge_request(5, state: 'opened', merge_status: 'unchecked')
+
+    stub_const("#{described_class.name}::BATCH_SIZE", 2)
+
+    Sidekiq::Testing.fake! do
+      Timecop.freeze do
+        migrate!
+
+        expect(described_class::MIGRATION)
+          .to be_scheduled_delayed_migration(5.minutes, 1, 2)
+
+        expect(described_class::MIGRATION)
+          .to be_scheduled_delayed_migration(10.minutes, 3, 3)
+
+        expect(BackgroundMigrationWorker.jobs.size).to eq(2)
+      end
+    end
+  end
+end