Add revert_backfill_conversion_of_integer_to_bigint migration helper

for easier revert of `backfill_conversion_of_integer_to_bigint`.

See https://gitlab.com/gitlab-org/gitlab/-/issues/328600.

lib/gitlab/database/migration_helpers.rb

@@ -1048,6 +1048,25 @@ module Gitlab
         end
       end
 
+      # Reverts `backfill_conversion_of_integer_to_bigint`
+      #
+      # table - The name of the database table containing the column
+      # columns - The name, or an array of names, of the column(s) we want to convert to bigint.
+      # primary_key - The name of the primary key column (most often :id)
+      def revert_backfill_conversion_of_integer_to_bigint(table, columns, primary_key: :id)
+        columns = Array.wrap(columns)
+
+        conditions = ActiveRecord::Base.sanitize_sql([
+          'job_class_name = :job_class_name AND table_name = :table_name AND column_name = :column_name AND job_arguments = :job_arguments',
+          job_class_name: 'CopyColumnUsingBackgroundMigrationJob',
+          table_name: table,
+          column_name: primary_key,
+          job_arguments: [columns, columns.map { |c| "#{c}_convert_to_bigint" }].to_json
+        ])
+
+        execute("DELETE FROM batched_background_migrations WHERE #{conditions}")
+      end
+
       # Performs a concurrent column rename when using PostgreSQL.
       def install_rename_triggers_for_postgresql(table, old, new, trigger_name: nil)
         Gitlab::Database::UnidirectionalCopyTrigger.on_table(table).create(old, new, trigger_name: trigger_name)

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -1921,6 +1921,54 @@ RSpec.describe Gitlab::Database::MigrationHelpers do
     end
   end
 
+  describe '#revert_backfill_conversion_of_integer_to_bigint' do
+    let(:table) { :_test_backfill_table }
+    let(:primary_key) { :id }
+
+    before do
+      model.create_table table, id: false do |t|
+        t.integer primary_key, primary_key: true
+        t.text :message, null: false
+        t.integer :other_id
+        t.timestamps
+      end
+
+      model.initialize_conversion_of_integer_to_bigint(table, columns, primary_key: primary_key)
+      model.backfill_conversion_of_integer_to_bigint(table, columns, primary_key: primary_key)
+    end
+
+    context 'when a single column is being converted' do
+      let(:columns) { :id }
+
+      it 'deletes the batched migration tracking record' do
+        expect do
+          model.revert_backfill_conversion_of_integer_to_bigint(table, columns)
+        end.to change { Gitlab::Database::BackgroundMigration::BatchedMigration.count }.by(-1)
+      end
+    end
+
+    context 'when a multiple columns are being converted' do
+      let(:columns) { [:id, :other_id] }
+
+      it 'deletes the batched migration tracking record' do
+        expect do
+          model.revert_backfill_conversion_of_integer_to_bigint(table, columns)
+        end.to change { Gitlab::Database::BackgroundMigration::BatchedMigration.count }.by(-1)
+      end
+    end
+
+    context 'when primary key column has custom name' do
+      let(:primary_key) { :other_pk }
+      let(:columns) { :other_id }
+
+      it 'deletes the batched migration tracking record' do
+        expect do
+          model.revert_backfill_conversion_of_integer_to_bigint(table, columns, primary_key: primary_key)
+        end.to change { Gitlab::Database::BackgroundMigration::BatchedMigration.count }.by(-1)
+      end
+    end
+  end
+
   describe '#index_exists_by_name?' do
     it 'returns true if an index exists' do
       ActiveRecord::Base.connection.execute(