When using the standard resequencer in Mediator, you must always specify a group XPath expression and a sequence ID XPath expression. These specify where the Mediator resequencer can find the group and the sequence ID in the messages. You must also supply the sequence numbering in terms of the start sequence ID and the sequence ID incremental delta. This numbering is used to form each group. In addition to the group, sequence ID, and increment properties, you can also specify a timeout period, in seconds, to wait for the expected messages.

The Mediator standard resequencer holds back messages in the Mediator resequencer database until it can produce the right sequence for different groups. This situation means that if for a given group, the message with a particular sequence ID does not arrive within the timeout period, the subsequent messages for that group are held back forever. In such a case, you must manually unlock the group through Oracle Enterprise Manager Fusion Middleware Control and go to the next available message, skipping the pending message.