A transaction identifier that is only unique within a raw store, do not ever pass this out of raw store. During reboot, all transaction Ids that have ever generated a log record will not be reused. However, if you put away the transaction Id of a read only transaction, then the is no guarentee that the transactionId won't be reused when the system reboots. It is much safer to store away the ExternalTrasanctionId rather than the transactionId. The equals() method for TransactionId implements by value equality. MT - immutable