DJ> Can you please explain how this implementation uses transactions and what DJ> transaction isolation settings it requires or assumes?
When transaction/new transaction comes, JDBCOptimisticLock locks fields and their values depending on the strategy used. Fields and field values are locked per each tx. For version columns and field group strategies, fields that are used in locking and their values are locked when tx reaches entity. For read and modified strategies, when tx reaches entity, all entitie's field values are locked but not the fields itself. Later, when a field is read/modified the field is actually locked. DJ> Does this DJ> implementation result in each JBoss jta transaction getting its own copy of DJ> any entity it accesses? Here you caught me... it occurs it's not so great. Using "Standard CMP 2.x EntityBean" container entities are shared between transactions. So, if some tx changes some field, another tx will see it. Using "Instance Per Transaction 2.x EntityBean" doesn't solve it either. DJ> Is it possible to setup optimistic locking without useing any extra checks DJ> or fields on a database such as firebird that natively supports aptimistic DJ> locking through versioning? No, no vendor support for now. Thanks, alex DJ> (On Firebird with Jaybird driver, setting isolation to Repeatable Read DJ> results in each transaction getting a snapshot of the database. If one DJ> transaction tries to modify a record already modified by another DJ> transaction, you get an exception. It is also possible to configure so the DJ> 2nd transaction waits for the first to complete before deciding whether to DJ> throw an exception.) DJ> Thanks! DJ> david jencks DJ> On 2002.12.26 03:50:57 -0500 Alex Loubyansky wrote: >> To setup optimistic locking, container configuration element >> locking-policy should be set to >> <locking-policy>org.jboss.ejb.plugins.lock.JDBCOptimisticLock</locking-policy> >> and entity element in jbosscmp-jdbc.xml should have optimistic-locking >> element. >> >> Following are the possible configurations of optimistic-locking element: >> 1. Fixed group of fields that will be used for optimistic locking. >> <optimistic-locking> >> <group-name>optimisticLockingGroup</group-name> >> </optimistic-locking> >> where optimisticLockingGroup is one of the entity's load-group-name's. >> >> 2. Modified strategy. The fields that were modified during transaction >> will be used for optimistic locking. >> <optimistic-locking> >> <modified-strategy/> >> </optimistic-locking> >> >> 3. Read strategy. The fields that were read during transaction will be >> used for optimistic locking. >> <optimistic-locking> >> <read-strategy/> >> </optimistic-locking> >> >> 4. Version (counter) column strategy. Additional version (counter) >> field of type java.lang.Long will be added to entity which >> will be used for optimistic locking. Each update of the entity will >> increase the value of its version field by 1. >> <optimistic-locking> >> <version-column/> >> <field-name>versionField</field-name> >> <column-name>ol_version</column-name> >> <jdbc-type>INTEGER</jdbc-type> >> <sql-type>INTEGER(5)</sql-type> >> </optimistic-locking> >> >> 5. Timestamp column strategy. Additional timestamp column field of >> type java.util.Date will be added to entity which will be >> used for optimistic locking. Each update of the entity will set the >> value of its timestamp field to the current time. >> <optimistic-locking> >> <timestamp-column/> >> <field-name>timestampField</field-name> >> <column-name>ol_timestamp</column-name> >> <jdbc-type>TIMESTAMP</jdbc-type> >> <sql-type>DATETIME</sql-type> >> </optimistic-locking> >> >> 6. Version column generated by KeyGenerator. Additional field will be >> added to entity that will be used for optimistic locking. Each update >> of the entity will update its version column with value generated by >> KeyGenerator. >> <optimistic-locking> >> <key-generator-factory>UUIDKeyGeneratorFactory</key-generator-factory> >> <field-type>java.lang.String</field-type> >> <field-name>uuidField</field-name> >> <column-name>ol_uuid</column-name> >> <jdbc-type>VARCHAR</jdbc-type> >> <sql-type>VARCHAR(32)</sql-type> >> </optimistic-locking> >> >> alex -- Best regards, Alex Loubyansky ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ JBoss-user mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/jboss-user
