Change migration table scopes to use id column

Change the scopes that are used to fetch batched_background_migrations
and batched_background_migration_jobs to use the `id` column rather than
`created_at`. This saves an index one of the tables, and ensures we
don't need a tiebreaker for the sort.

db/migrate/20210128172149_create_background_migration_tracking_tables.rb

@@ -47,7 +47,7 @@ class CreateBackgroundMigrationTrackingTables < ActiveRecord::Migration[6.0]
       t.integer :status, limit: 2, null: false, default: 0
       t.integer :attempts, limit: 2, null: false, default: 0
 
-      t.index [:batched_background_migration_id, :created_at], name: :index_batched_jobs_by_batched_migration_id_created_at
+      t.index [:batched_background_migration_id, :id], name: :index_batched_jobs_by_batched_migration_id_and_id
     end
   end
 

db/structure.sql

@@ -21705,7 +21705,7 @@ CREATE INDEX index_badges_on_group_id ON badges USING btree (group_id);
 
 CREATE INDEX index_badges_on_project_id ON badges USING btree (project_id);
 
-CREATE INDEX index_batched_jobs_by_batched_migration_id_created_at ON batched_background_migration_jobs USING btree (batched_background_migration_id, created_at);
+CREATE INDEX index_batched_jobs_by_batched_migration_id_and_id ON batched_background_migration_jobs USING btree (batched_background_migration_id, id);
 
 CREATE INDEX index_batched_migrations_on_job_table_and_column_name ON batched_background_migrations USING btree (job_class_name, table_name, column_name);
 

lib/gitlab/database/background_migration/batched_migration.rb

@@ -7,11 +7,11 @@ module Gitlab
         self.table_name = :batched_background_migrations
 
         has_many :batched_jobs, foreign_key: :batched_background_migration_id
-        has_one :last_job, -> { order(created_at: :desc) },
+        has_one :last_job, -> { order(id: :desc) },
           class_name: 'Gitlab::Database::BackgroundMigration::BatchedJob',
           foreign_key: :batched_background_migration_id
 
-        scope :queue_order, -> { order(created_at: :asc) }
+        scope :queue_order, -> { order(id: :asc) }
 
         enum status: {
           paused: 0,

lib/gitlab/database/background_migration/batched_migration_wrapper.rb

@@ -5,9 +5,6 @@ module Gitlab
     module BackgroundMigration
       class BatchedMigrationWrapper
         def perform(batch_tracking_record)
-          return if batch_tracking_record.migration_aborted?
-
-          begin
           start_tracking_execution(batch_tracking_record)
 
           execute_batch(batch_tracking_record)
@@ -20,7 +17,6 @@ module Gitlab
         ensure
           finish_tracking_execution(batch_tracking_record)
         end
-        end
 
         private
 

spec/lib/gitlab/database/background_migration/batched_job_spec.rb

@@ -13,7 +13,7 @@ RSpec.describe Gitlab::Database::BackgroundMigration::BatchedJob, type: :model d
     let(:batched_job) { build(:batched_background_migration_job) }
     let(:batched_migration) { batched_job.batched_migration }
 
-    describe '#migration_job_class' do
+    describe '#migration_aborted?' do
       before do
         batched_migration.status = :aborted
       end

spec/lib/gitlab/database/background_migration/batched_migration_spec.rb

@@ -11,21 +11,21 @@ RSpec.describe Gitlab::Database::BackgroundMigration::BatchedMigration, type: :m
     describe '#last_job' do
       let!(:batched_migration) { create(:batched_background_migration) }
       let!(:batched_job1) { create(:batched_background_migration_job, batched_migration: batched_migration) }
-      let!(:batched_job2) { create(:batched_background_migration_job, batched_migration: batched_migration, created_at: 1.month.ago) }
+      let!(:batched_job2) { create(:batched_background_migration_job, batched_migration: batched_migration) }
 
-      it 'returns the most recently created batch_job' do
-        expect(batched_migration.last_job).to eq(batched_job1)
+      it 'returns the most recent (in order of id) batched job' do
+        expect(batched_migration.last_job).to eq(batched_job2)
       end
     end
   end
 
   describe '.queue_order' do
-    let!(:migration1) { create(:batched_background_migration, created_at: 1.month.ago) }
-    let!(:migration2) { create(:batched_background_migration, created_at: 2.months.ago) }
+    let!(:migration1) { create(:batched_background_migration) }
+    let!(:migration2) { create(:batched_background_migration) }
     let!(:migration3) { create(:batched_background_migration) }
 
-    it 'returns batched_migrations ordered by created_at' do
-      expect(described_class.queue_order.all).to eq([migration2, migration1, migration3])
+    it 'returns batched migrations ordered by their id' do
+      expect(described_class.queue_order.all).to eq([migration1, migration2, migration3])
     end
   end
 

spec/lib/gitlab/database/background_migration/batched_migration_wrapper_spec.rb

@@ -8,28 +8,6 @@ RSpec.describe Gitlab::Database::BackgroundMigration::BatchedMigrationWrapper, '
 
   let_it_be(:active_migration) { create(:batched_background_migration, :active, job_arguments: [:id, :other_id]) }
 
-  context 'when the migration is aborted' do
-    let!(:aborted_migration) { create(:batched_background_migration, :aborted) }
-    let!(:job_record) { create(:batched_background_migration_job, batched_migration: aborted_migration) }
-
-    it 'does not run the migration job instance' do
-      expect(job_record).not_to receive(:migration_job_class)
-      expect(job_class).not_to receive(:new)
-
-      migration_wrapper.perform(job_record)
-    end
-
-    it 'does not update the tracking record in the database' do
-      migration_wrapper.perform(job_record)
-
-      reloaded_job_record = job_record.reload
-
-      expect(reloaded_job_record).to be_pending
-      expect(reloaded_job_record.attempts).to eq(0)
-    end
-  end
-
-  context 'when the migration is not aborted' do
   let!(:job_record) { create(:batched_background_migration_job, batched_migration: active_migration) }
 
   it 'runs the migration job' do
@@ -89,5 +67,4 @@ RSpec.describe Gitlab::Database::BackgroundMigration::BatchedMigrationWrapper, '
       end
     end
   end
-  end
 end

spec/lib/gitlab/database/background_migration/scheduler_spec.rb

@@ -32,8 +32,8 @@ RSpec.describe Gitlab::Database::BackgroundMigration::Scheduler, '#perform' do
   end
 
   context 'when there are active migrations' do
-    let!(:last_migration) { create(:batched_background_migration, :active, created_at: 1.month.ago) }
-    let!(:first_migration) { create(:batched_background_migration, :active, batch_size: 2, created_at: 2.months.ago) }
+    let!(:first_migration) { create(:batched_background_migration, :active, batch_size: 2) }
+    let!(:last_migration) { create(:batched_background_migration, :active) }
 
     let(:job_relation) do
       Gitlab::Database::BackgroundMigration::BatchedJob.where(batched_background_migration_id: first_migration.id)