Disable migration to backfill design positions

We don't actually need this anymore, since we're now also backfilling
immediately before moving a design.

db/post_migrate/20200724130639_backfill_designs_relative_position.rb

 # frozen_string_literal: true
 
+# This migration is not needed anymore and was disabled, because we're now
+# also backfilling design positions immediately before moving a design.
+#
+# See https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39555
 class BackfillDesignsRelativePosition < ActiveRecord::Migration[6.0]
   include Gitlab::Database::MigrationHelpers
 
   DOWNTIME = false
-  INTERVAL = 2.minutes
-  BATCH_SIZE = 1000
-  MIGRATION = 'BackfillDesignsRelativePosition'
-
-  disable_ddl_transaction!
-
-  class Issue < ActiveRecord::Base
-    include EachBatch
-
-    self.table_name = 'issues'
-
-    has_many :designs
-  end
-
-  class Design < ActiveRecord::Base
-    self.table_name = 'design_management_designs'
-  end
 
   def up
-    issues_with_designs = Issue.where(id: Design.select(:issue_id))
-
-    issues_with_designs.each_batch(of: BATCH_SIZE) do |relation, index|
-      issue_ids = relation.pluck(:id)
-      delay = INTERVAL * index
-
-      migrate_in(delay, MIGRATION, [issue_ids])
-    end
+    # no-op
   end
 
   def down
+    # no-op
   end
 end

doc/development/deleting_migrations.md

@@ -23,7 +23,7 @@ Migrations can be disabled if:
 In order to disable a migration, the following steps apply to all types of migrations:
 
 1. Turn the migration into a no-op by removing the code inside `#up`, `#down`
-  or `#perform` methods, and adding `#no-op` comment instead.
+  or `#perform` methods, and adding `# no-op` comment instead.
 1. Add a comment explaining why the code is gone.
 
 Disabling migrations requires explicit approval of Database Maintainer.

lib/gitlab/background_migration/backfill_designs_relative_position.rb

@@ -2,52 +2,13 @@
 
 module Gitlab
   module BackgroundMigration
-    # Backfill `relative_position` column in `design_management_designs` table
+    # This migration is not needed anymore and was disabled, because we're now
+    # also backfilling design positions immediately before moving a design.
+    #
+    # See https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39555
     class BackfillDesignsRelativePosition
-      # Define the issue model
-      class Issue < ActiveRecord::Base
-        self.table_name = 'issues'
-      end
-
-      # Define the design model
-      class Design < ActiveRecord::Base
-        include RelativePositioning if defined?(RelativePositioning)
-
-        self.table_name = 'design_management_designs'
-
-        def self.relative_positioning_query_base(design)
-          where(issue_id: design.issue_id)
-        end
-
-        def self.relative_positioning_parent_column
-          :issue_id
-        end
-
-        def self.move_nulls_to_start(designs)
-          if defined?(super)
-            super(designs)
-          else
-            logger.error "BackfillDesignsRelativePosition failed because move_nulls_to_start is no longer included in the RelativePositioning concern"
-          end
-        end
-      end
-
       def perform(issue_ids)
-        issue_ids.each do |issue_id|
-          migrate_issue(issue_id)
-        end
-      end
-
-      private
-
-      def migrate_issue(issue_id)
-        issue = Issue.find_by(id: issue_id)
-        return unless issue
-
-        designs = Design.where(issue_id: issue.id).order(:id)
-        return unless designs.any?
-
-        Design.move_nulls_to_start(designs)
+        # no-op
       end
     end
   end

spec/lib/gitlab/background_migration/backfill_designs_relative_position_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-
-RSpec.describe Gitlab::BackgroundMigration::BackfillDesignsRelativePosition do
-  let(:namespace) { table(:namespaces).create!(name: 'gitlab', path: 'gitlab') }
-  let(:project) { table(:projects).create!(namespace_id: namespace.id) }
-  let(:issues) { table(:issues) }
-  let(:designs) { table(:design_management_designs) }
-
-  before do
-    issues.create!(id: 1, project_id: project.id)
-    issues.create!(id: 2, project_id: project.id)
-    issues.create!(id: 3, project_id: project.id)
-    issues.create!(id: 4, project_id: project.id)
-
-    designs.create!(id: 1, issue_id: 1, project_id: project.id, filename: 'design1.jpg')
-    designs.create!(id: 2, issue_id: 1, project_id: project.id, filename: 'design2.jpg')
-    designs.create!(id: 3, issue_id: 2, project_id: project.id, filename: 'design3.jpg')
-    designs.create!(id: 4, issue_id: 2, project_id: project.id, filename: 'design4.jpg')
-    designs.create!(id: 5, issue_id: 3, project_id: project.id, filename: 'design5.jpg')
-  end
-
-  describe '#perform' do
-    it 'backfills the position for the designs in each issue' do
-      expect(described_class::Design).to receive(:move_nulls_to_start).with(
-        a_collection_containing_exactly(
-          an_object_having_attributes(id: 1, issue_id: 1),
-          an_object_having_attributes(id: 2, issue_id: 1)
-        )
-      ).ordered.and_call_original
-
-      expect(described_class::Design).to receive(:move_nulls_to_start).with(
-        a_collection_containing_exactly(
-          an_object_having_attributes(id: 3, issue_id: 2),
-          an_object_having_attributes(id: 4, issue_id: 2)
-        )
-      ).ordered.and_call_original
-
-      # We only expect calls to `move_nulls_to_start` with issues 1 and 2:
-      # - Issue 3 should be skipped because we're not passing its ID
-      # - Issue 4 should be skipped because it doesn't have any designs
-      # - Issue 0 should be skipped because it doesn't exist
-      subject.perform([1, 2, 4, 0])
-
-      expect(designs.find(1).relative_position).to be < designs.find(2).relative_position
-      expect(designs.find(3).relative_position).to be < designs.find(4).relative_position
-      expect(designs.find(5).relative_position).to be_nil
-    end
-  end
-end

spec/migrations/backfill_designs_relative_position_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-require Rails.root.join('db', 'post_migrate', '20200724130639_backfill_designs_relative_position.rb')
-
-RSpec.describe BackfillDesignsRelativePosition do
-  let(:namespace) { table(:namespaces).create!(name: 'gitlab', path: 'gitlab') }
-  let(:project) { table(:projects).create!(namespace_id: namespace.id) }
-  let(:issues) { table(:issues) }
-  let(:designs) { table(:design_management_designs) }
-
-  before do
-    issues.create!(id: 1, project_id: project.id)
-    issues.create!(id: 2, project_id: project.id)
-    issues.create!(id: 3, project_id: project.id)
-    issues.create!(id: 4, project_id: project.id)
-
-    designs.create!(issue_id: 1, project_id: project.id, filename: 'design1.jpg')
-    designs.create!(issue_id: 2, project_id: project.id, filename: 'design2.jpg')
-    designs.create!(issue_id: 4, project_id: project.id, filename: 'design3.jpg')
-
-    stub_const("#{described_class.name}::BATCH_SIZE", 2)
-  end
-
-  it 'correctly schedules background migrations' do
-    Sidekiq::Testing.fake! do
-      Timecop.freeze do
-        migrate!
-
-        expect(described_class::MIGRATION)
-          .to be_scheduled_delayed_migration(2.minutes, [1, 2])
-
-        expect(described_class::MIGRATION)
-          .to be_scheduled_delayed_migration(4.minutes, [4])
-
-        # Issue 3 should be skipped because it doesn't have any designs
-        expect(BackgroundMigrationWorker.jobs.size).to eq(2)
-      end
-    end
-  end
-end