Use a background migration for issues.closed_atchange-issues-closed-at-background-migration

In a previous attempt (rolled back in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16021) we tried
to migrate `issues.closed_at` from timestamp to timestamptz using a
regular migration. This has a bad impact on GitLab.com and as such was
rolled back.

This commit re-implements the original migrations using generic
background migrations, allowing us to still migrate the data in a single
release but without a negative impact on availability.

To ensure the database schema is up to date the background migrations
are performed inline in development and test environments. We also make
sure to not migrate that that doesn't need migrating in the first place
or has already been migrated.

1 files changed, 90 insertions, 1 deletions

diff --git a/spec/lib/gitlab/database/migration_helpers_spec.rb b/spec/lib/gitlab/database/migration_helpers_spec.rb
index 664ba0f7234..7727a1d81b1 100644
--- a/spec/lib/gitlab/database/migration_helpers_spec.rb
+++ b/spec/lib/gitlab/database/migration_helpers_spec.rb
@@ -902,7 +902,7 @@ describe Gitlab::Database::MigrationHelpers do
   describe '#check_trigger_permissions!' do
     it 'does nothing when the user has the correct permissions' do
       expect { model.check_trigger_permissions!('users') }
-        .not_to raise_error(RuntimeError)
+        .not_to raise_error
     end
 
     it 'raises RuntimeError when the user does not have the correct permissions' do
@@ -1036,4 +1036,93 @@ describe Gitlab::Database::MigrationHelpers do
       end
     end
   end
+
+  describe '#change_column_type_using_background_migration' do
+    let!(:issue) { create(:issue) }
+
+    let(:issue_model) do
+      Class.new(ActiveRecord::Base) do
+        self.table_name = 'issues'
+        include EachBatch
+      end
+    end
+
+    it 'changes the type of a column using a background migration' do
+      expect(model)
+        .to receive(:add_column)
+        .with('issues', 'closed_at_for_type_change', :datetime_with_timezone)
+
+      expect(model)
+        .to receive(:install_rename_triggers)
+        .with('issues', :closed_at, 'closed_at_for_type_change')
+
+      expect(BackgroundMigrationWorker)
+        .to receive(:perform_in)
+        .ordered
+        .with(
+          10.minutes,
+          'CopyColumn',
+          ['issues', :closed_at, 'closed_at_for_type_change', issue.id, issue.id]
+        )
+
+      expect(BackgroundMigrationWorker)
+        .to receive(:perform_in)
+        .ordered
+        .with(
+          1.hour + 10.minutes,
+          'CleanupConcurrentTypeChange',
+          ['issues', :closed_at, 'closed_at_for_type_change']
+        )
+
+      expect(Gitlab::BackgroundMigration)
+        .to receive(:steal)
+        .ordered
+        .with('CopyColumn')
+
+      expect(Gitlab::BackgroundMigration)
+        .to receive(:steal)
+        .ordered
+        .with('CleanupConcurrentTypeChange')
+
+      model.change_column_type_using_background_migration(
+        issue_model.all,
+        :closed_at,
+        :datetime_with_timezone
+      )
+    end
+  end
+
+  describe '#perform_background_migration_inline?' do
+    it 'returns true in a test environment' do
+      allow(Rails.env)
+        .to receive(:test?)
+        .and_return(true)
+
+      expect(model.perform_background_migration_inline?).to eq(true)
+    end
+
+    it 'returns true in a development environment' do
+      allow(Rails.env)
+        .to receive(:test?)
+        .and_return(false)
+
+      allow(Rails.env)
+        .to receive(:development?)
+        .and_return(true)
+
+      expect(model.perform_background_migration_inline?).to eq(true)
+    end
+
+    it 'returns false in a production environment' do
+      allow(Rails.env)
+        .to receive(:test?)
+        .and_return(false)
+
+      allow(Rails.env)
+        .to receive(:development?)
+        .and_return(false)
+
+      expect(model.perform_background_migration_inline?).to eq(false)
+    end
+  end
 end