Restrictions on optimized message transfers

does not chain the following SQL statements even when you enable optimized message transfers:
  • COMMIT WORK
  • DESCRIBE
  • EXECUTE
  • FETCH
  • FLUSH
  • PREPARE
  • PUT
  • ROLLBACK WORK
  • SELECT INTO (singleton SELECT)

When reaches one of the preceding statements, it flushes the message out to the database server. then continues message chaining for subsequent SQL statements. Only SQL statements that require network traffic cause to flush the message queue.

SQL statements that do not require network traffic, such as the DECLARE statement, do not cause to send the message queue to the database server.