Disable ScheduleCalculateWikiSizes migration and remove technical debt

In this commit we disabled the ScheduleCalculateWikiSizes migration
because it's forcing us to have some technical debt code in the
ProjectStatistics code.

By the time of this commit, inside 14.0 release, the migration
should have already run, so it's safe to disabled it.

app/models/project_statistics.rb

@@ -94,18 +94,14 @@ class ProjectStatistics < ApplicationRecord
   end
 
   def update_storage_size
-    storage_size = repository_size + wiki_size + lfs_objects_size + build_artifacts_size + packages_size
-    # The `snippets_size` column was added on 20200622095419 but db/post_migrate/20190527194900_schedule_calculate_wiki_sizes.rb
-    # might try to update project statistics before the `snippets_size` column has been created.
-    storage_size += snippets_size if self.class.column_names.include?('snippets_size')
-
-    # The `pipeline_artifacts_size` column was added on 20200817142800 but db/post_migrate/20190527194900_schedule_calculate_wiki_sizes.rb
-    # might try to update project statistics before the `pipeline_artifacts_size` column has been created.
-    storage_size += pipeline_artifacts_size if self.class.column_names.include?('pipeline_artifacts_size')
-
-    # The `uploads_size` column was added on 20201105021637 but db/post_migrate/20190527194900_schedule_calculate_wiki_sizes.rb
-    # might try to update project statistics before the `uploads_size` column has been created.
-    storage_size += uploads_size if self.class.column_names.include?('uploads_size')
+    storage_size = repository_size +
+                   wiki_size +
+                   lfs_objects_size +
+                   build_artifacts_size +
+                   packages_size +
+                   snippets_size +
+                   pipeline_artifacts_size +
+                   uploads_size
 
     self.storage_size = storage_size
   end

db/post_migrate/20190527194900_schedule_calculate_wiki_sizes.rb

@@ -18,12 +18,12 @@ class ScheduleCalculateWikiSizes < ActiveRecord::Migration[5.0]
 
   disable_ddl_transaction!
 
+  # Disabling this old migration because it should already run
+  # in 14.0. This will allow us to remove some `technical debt`
+  # in ProjectStatistics model, because of some columns
+  # not present by the time the migration is run.
   def up
-    queue_background_migration_jobs_by_range_at_intervals(
-      ::ScheduleCalculateWikiSizes::ProjectStatistics.without_wiki_size,
-      MIGRATION,
-      BATCH_TIME,
-      batch_size: BATCH_SIZE)
+    # no-op
   end
 
   def down

spec/migrations/schedule_calculate_wiki_sizes_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-require Rails.root.join('db', 'post_migrate', '20190527194900_schedule_calculate_wiki_sizes.rb')
-
-RSpec.describe ScheduleCalculateWikiSizes do
-  let(:migration_class) { Gitlab::BackgroundMigration::CalculateWikiSizes }
-  let(:migration_name)  { migration_class.to_s.demodulize }
-
-  let(:namespaces) { table(:namespaces) }
-  let(:projects) { table(:projects) }
-  let(:project_statistics) { table(:project_statistics) }
-  let(:namespace) { namespaces.create!(name: 'wiki-migration', path: 'wiki-migration') }
-  let(:project1) { projects.create!(name: 'wiki-project-1', path: 'wiki-project-1', namespace_id: namespace.id) }
-  let(:project2) { projects.create!(name: 'wiki-project-2', path: 'wiki-project-2', namespace_id: namespace.id) }
-  let(:project3) { projects.create!(name: 'wiki-project-3', path: 'wiki-project-3', namespace_id: namespace.id) }
-
-  context 'when missing wiki sizes exist' do
-    let!(:project_statistic1) { project_statistics.create!(project_id: project1.id, namespace_id: namespace.id, wiki_size: 1000) }
-    let!(:project_statistic2) { project_statistics.create!(project_id: project2.id, namespace_id: namespace.id, wiki_size: nil) }
-    let!(:project_statistic3) { project_statistics.create!(project_id: project3.id, namespace_id: namespace.id, wiki_size: nil) }
-
-    it 'schedules a background migration' do
-      freeze_time do
-        migrate!
-
-        expect(migration_name).to be_scheduled_delayed_migration(5.minutes, project_statistic2.id, project_statistic3.id)
-        expect(BackgroundMigrationWorker.jobs.size).to eq 1
-      end
-    end
-
-    it 'calculates missing wiki sizes', :sidekiq_inline do
-      expect(project_statistic2.wiki_size).to be_nil
-      expect(project_statistic3.wiki_size).to be_nil
-
-      migrate!
-
-      expect(project_statistic2.reload.wiki_size).not_to be_nil
-      expect(project_statistic3.reload.wiki_size).not_to be_nil
-    end
-  end
-
-  context 'when missing wiki sizes do not exist' do
-    before do
-      namespace = namespaces.create!(name: 'wiki-migration', path: 'wiki-migration')
-      project = projects.create!(name: 'wiki-project-1', path: 'wiki-project-1', namespace_id: namespace.id)
-      project_statistics.create!(project_id: project.id, namespace_id: namespace.id, wiki_size: 1000)
-    end
-
-    it 'does not schedule a background migration' do
-      Sidekiq::Testing.fake! do
-        freeze_time do
-          migrate!
-
-          expect(BackgroundMigrationWorker.jobs.size).to eq 0
-        end
-      end
-    end
-  end
-end