transaction_isolation_levels

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 240
      def transaction_isolation_levels
        {
          read_uncommitted: "READ UNCOMMITTED",
          read_committed:   "READ COMMITTED",
          repeatable_read:  "REPEATABLE READ",
          serializable:     "SERIALIZABLE"
        }
      end