Change primary key definition to bigint

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/221091

lib/gitlab/database/partitioning_migration_helpers/table_management_helpers.rb

@@ -109,9 +109,18 @@ module Gitlab
             remove_column(table_name, partition_column.name)
             rename_column(table_name, tmp_column_name, partition_column.name)
             change_column_default(table_name, primary_key, nil)
+
+            if column_of_type?(table_name, primary_key, :integer)
+              # Default to int8 primary keys to prevent overflow
+              change_column(table_name, primary_key, :bigint)
+            end
           end
         end
 
+        def column_of_type?(table_name, column, type)
+          find_column_definition(table_name, column).type == type
+        end
+
         def create_daterange_partitions(table_name, column_name, min_date, max_date)
           min_date = min_date.beginning_of_month.to_date
           max_date = max_date.next_month.beginning_of_month.to_date

spec/lib/gitlab/database/partitioning_migration_helpers/table_management_helpers_spec.rb

@@ -111,6 +111,36 @@ describe Gitlab::Database::PartitioningMigrationHelpers::TableManagementHelpers
         expect_table_partitioned_by(partitioned_table, [partition_column])
       end
 
+      it 'changes the primary key datatype to bigint' do
+        migration.partition_table_by_date template_table, partition_column, min_date: min_date, max_date: max_date
+
+        pk_column = connection.columns(partitioned_table).find { |c| c.name == old_primary_key }
+
+        expect(pk_column.sql_type).to eq('bigint')
+      end
+
+      context 'with a non-integer primary key datatype' do
+        before do
+          connection.create_table :another_example, id: false do |t|
+            t.string :identifier, primary_key: true
+            t.timestamp :created_at
+          end
+        end
+
+        let(:template_table) { :another_example }
+        let(:old_primary_key) { 'identifier' }
+
+        it 'does not change the primary key datatype' do
+          migration.partition_table_by_date template_table, partition_column, min_date: min_date, max_date: max_date
+
+          original_pk_column = connection.columns(template_table).find { |c| c.name == old_primary_key }
+          pk_column = connection.columns(partitioned_table).find { |c| c.name == old_primary_key }
+
+          expect(pk_column).not_to be_nil
+          expect(pk_column).to eq(original_pk_column)
+        end
+      end
+
       it 'removes the default from the primary key column' do
         migration.partition_table_by_date template_table, partition_column, min_date: min_date, max_date: max_date