126 Transaction management If the NontransactionalWrite flag on
126 Transaction management If the NontransactionalWrite flag on a Transaction is true, then the field values of Persistent-Nontransactional instances can be updated without an active transaction. Each of these capabilities is an optional feature in the JDO specification. 7.5 Transaction modes to improve efficiency JDO defines two additional transaction modes intended to improve efficiency. These are RestoreValues and RetainValues. Note that the setting of these flags only affects instances in memory, and does not alter the effect of commit or rollback processing on the data store. 7.5.1 RestoreValues The setting of the RestoreValues flag affects the treatment of instances in memory as a result of transaction rollback. If the RestoreValues flag is true, instances involved in a transaction that is rolled back will have their field values restored to their original values. These were cached when the transaction was begun. If the RestoreValues flag is false, instances involved in a transaction that is rolled back will be transitioned to Hollow. In such a state they do not have field values loaded, and thus the field values do not need to be restored to their original values. This allows JDO vendors to optimize their implementations so that instance values are not cached in the first place. If the now Hollow instance is accessed by the application, persistent fields will be loaded from the data store at that time. Setting RestoreValues to false can yield significant performance improvements if your application does not refer to instances after transaction rollback. 7.5.2 RetainValues This flag determines what action is taken by the persistence manager on persistent instances in memory after a transaction has been successfully committed. If RetainValues is false (the default setting), instances are automatically evicted on transaction commit, transitioning to Hollow. This limits the size of the instance cache and improves performance. If RetainValues is true, this automatic eviction does not take place. The persistent instances remain cached in the Persistent-Nontransactional state until they are once again used transactionally, or evicted. Eviction may be performed explicitly by the developer, or implicitly by the persistence manager to free up cache resources. This setting can improve performance of applications that work with the same set of instances across a number of independent transactions, at the expense of greater resource utilization by the persistence manager.
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