Make DeleteConflictingRedirectRoutes no-op

Both the post-deploy and background migration.

changelogs/unreleased/mk-no-op-delete-conflicting-redirects.yml

+---
+title: Prevent excessive DB load due to faulty DeleteConflictingRedirectRoutes background
+  migration
+merge_request: 16205
+author:
+type: fixed

db/post_migrate/20170907170235_delete_conflicting_redirect_routes.rb

@@ -2,36 +2,12 @@
 # for more information on how to write migrations for GitLab.
 
 class DeleteConflictingRedirectRoutes < ActiveRecord::Migration
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-  MIGRATION = 'DeleteConflictingRedirectRoutesRange'.freeze
-  BATCH_SIZE = 200 # At 200, I expect under 20s per batch, which is under our query timeout of 60s.
-  DELAY_INTERVAL = 12.seconds
-
-  disable_ddl_transaction!
-
-  class Route < ActiveRecord::Base
-    include EachBatch
-
-    self.table_name = 'routes'
-  end
-
   def up
-    say opening_message
-
-    queue_background_migration_jobs_by_range_at_intervals(Route, MIGRATION, DELAY_INTERVAL, batch_size: BATCH_SIZE)
+    # No-op.
+    # See https://gitlab.com/gitlab-com/infrastructure/issues/3460#note_53223252
   end
 
   def down
     # nothing
   end
-
-  def opening_message
-    <<~MSG
-      Clean up redirect routes that conflict with regular routes.
-         See initial bug fix:
-         https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13357
-    MSG
-  end
 end

lib/gitlab/background_migration/delete_conflicting_redirect_routes_range.rb

 # frozen_string_literal: true
-# rubocop:disable Metrics/LineLength
 # rubocop:disable Style/Documentation
 
 module Gitlab
   module BackgroundMigration
     class DeleteConflictingRedirectRoutesRange
-      class Route < ActiveRecord::Base
-        self.table_name = 'routes'
-      end
-
-      class RedirectRoute < ActiveRecord::Base
-        self.table_name = 'redirect_routes'
-      end
-
-      # start_id - The start ID of the range of events to process
-      # end_id - The end ID of the range to process.
       def perform(start_id, end_id)
-        return unless migrate?
-
-        conflicts = RedirectRoute.where(routes_match_redirects_clause(start_id, end_id))
-        num_rows = conflicts.delete_all
-
-        Rails.logger.info("Gitlab::BackgroundMigration::DeleteConflictingRedirectRoutesRange [#{start_id}, #{end_id}] - Deleted #{num_rows} redirect routes that were conflicting with routes.")
-      end
-
-      def migrate?
-        Route.table_exists? && RedirectRoute.table_exists?
-      end
-
-      def routes_match_redirects_clause(start_id, end_id)
-        <<~ROUTES_MATCH_REDIRECTS
-          EXISTS (
-            SELECT 1 FROM routes
-            WHERE (
-              LOWER(redirect_routes.path) = LOWER(routes.path)
-              OR LOWER(redirect_routes.path) LIKE LOWER(CONCAT(routes.path, '/%'))
-            )
-            AND routes.id BETWEEN #{start_id} AND #{end_id}
-          )
-        ROUTES_MATCH_REDIRECTS
+        # No-op.
+        # See https://gitlab.com/gitlab-com/infrastructure/issues/3460#note_53223252
       end
     end
   end

spec/lib/gitlab/background_migration/delete_conflicting_redirect_routes_range_spec.rb

@@ -24,17 +24,12 @@ describe Gitlab::BackgroundMigration::DeleteConflictingRedirectRoutesRange, :mig
     redirect_routes.create!(source_id: 1, source_type: 'Namespace', path: 'foo5')
   end
 
-  it 'deletes the conflicting redirect_routes in the range' do
+  # No-op. See https://gitlab.com/gitlab-com/infrastructure/issues/3460#note_53223252
+  it 'NO-OP: does not delete any redirect_routes' do
     expect(redirect_routes.count).to eq(8)
 
-    expect do
-      described_class.new.perform(1, 3)
-    end.to change { redirect_routes.where("path like 'foo%'").count }.from(5).to(2)
+    described_class.new.perform(1, 5)
 
-    expect do
-      described_class.new.perform(4, 5)
-    end.to change { redirect_routes.where("path like 'foo%'").count }.from(2).to(0)
-
-    expect(redirect_routes.count).to eq(3)
+    expect(redirect_routes.count).to eq(8)
   end
 end

spec/migrations/delete_conflicting_redirect_routes_spec.rb

@@ -10,9 +10,6 @@ describe DeleteConflictingRedirectRoutes, :migration, :sidekiq do
   end
 
   before do
-    stub_const("DeleteConflictingRedirectRoutes::BATCH_SIZE", 2)
-    stub_const("Gitlab::Database::MigrationHelpers::BACKGROUND_MIGRATION_JOB_BUFFER_SIZE", 2)
-
     routes.create!(id: 1, source_id: 1, source_type: 'Namespace', path: 'foo1')
     routes.create!(id: 2, source_id: 2, source_type: 'Namespace', path: 'foo2')
     routes.create!(id: 3, source_id: 3, source_type: 'Namespace', path: 'foo3')
@@ -32,27 +29,14 @@ describe DeleteConflictingRedirectRoutes, :migration, :sidekiq do
     redirect_routes.create!(source_id: 1, source_type: 'Namespace', path: 'foo5')
   end
 
-  it 'correctly schedules background migrations' do
+  # No-op. See https://gitlab.com/gitlab-com/infrastructure/issues/3460#note_53223252
+  it 'NO-OP: does not schedule any background migrations' do
     Sidekiq::Testing.fake! do
       Timecop.freeze do
         migrate!
 
-        expect(BackgroundMigrationWorker.jobs[0]['args']).to eq([described_class::MIGRATION, [1, 2]])
-        expect(BackgroundMigrationWorker.jobs[0]['at']).to eq(12.seconds.from_now.to_f)
-        expect(BackgroundMigrationWorker.jobs[1]['args']).to eq([described_class::MIGRATION, [3, 4]])
-        expect(BackgroundMigrationWorker.jobs[1]['at']).to eq(24.seconds.from_now.to_f)
-        expect(BackgroundMigrationWorker.jobs[2]['args']).to eq([described_class::MIGRATION, [5, 5]])
-        expect(BackgroundMigrationWorker.jobs[2]['at']).to eq(36.seconds.from_now.to_f)
-        expect(BackgroundMigrationWorker.jobs.size).to eq 3
+        expect(BackgroundMigrationWorker.jobs.size).to eq 0
       end
     end
   end
-
-  it 'schedules background migrations' do
-    Sidekiq::Testing.inline! do
-      expect do
-        migrate!
-      end.to change { redirect_routes.count }.from(8).to(3)
-    end
-  end
 end