Design Specification: Database Change Event Cache Invalidation
|Date||Author||Version Description & Notes|
|2011-09-13||James||0.2 Updated API|
Some databases support raising change events when tables are updated or changed. It is also possible in some databases to raise events from triggers, and some third party products support raising database change events.
When a share cache is used in EclipseLink it can become stale if other applications (or other nodes) update the database directly.
This project will provide an infrastructure for supporting database change events to invalidate the changed objects in the EclipseLink shared cache.
Oracle's Database Change event Notification will be supported for Oracle databases.
Oracle DCN : The Oracle database Database Change event Notification feature available since Oracle 10.2.
- Support generic database change event listener.
- Support Oracle DCN
- Support cache invalidation of change objects.
- Must support database events with limited information, such as only the table ROWID.
- Add a DatabaseEventListener interface and to DatabaseSessionImpl (Database and Server sessions).
- Give register/remove callbacks on login/logout.
- Add OracleChangeNotificationListener to Oracle with Oracle JDBC dependencies.
- Register with database on login, remove on logout. Register all tracked tables.
- Oracle DCN only gives table name and ROWID, no primary key, so need to match ROWID with ID.
- Adds ROWID and a cache index on ROWID to all tracked descriptors.
- All objects read will be indexed by ROWID from cache index.
- Add insert callback to select ROWID and index in cache.
- On any update or delete get the transaction id and store in the unit of work properties.
- On merge for updates include the transaction id in the CacheKey
- When a DCN event is received find the CacheKey for the ROWID, and invalidate unless its transaction id matches the events transaction id.
- Add a DatabaseChangeNotificationType to CachePolicy to allow a descriptor to be configured to receive change events.
- Add a persistence unit default property for databaseChangeNotificationType.
- Only the primary table is supported. For secondary tables, or relationships usage of optimistic locking is required to ensure the primary table is always updated.
Add a JPA test model for DCN testing to the Oracle tests. Test:
- multiple tables (with versioning)
- relationships (with versioning)
- ensure objects invalidated in other session
- test native SQL queries
- test update-all queries
- DatabaseChangeNotificationType (NONE, INVALIDATE)
- setDatabaseEventListener(DatabaseEventListener )
- DatabaseEventListener (org.eclipse.persistence.platform.database.events)
- OracleChangeNotificationListener (org.eclipse.persistence.platform.oracle.dcn)
- persistence.xml - property
Should be documented under caching section, and Oracle section.
Need to document limitations is secondary table and relationship support. Warnings should be logged if version locking is not used.
|Issue #||Owner||Description / Notes|
|1||How to handle secondary tables and relationships?|
|2||How to integrate with third party cache support?|
|3||How should a descriptor be configured to use database change notification?|
|Issue||Description / Notes||Decision|
|1||How to handle secondary tables and relationships?||Require usage of optimistic locking, so the primary table is always updated.|
|2||Oracle DCN was renamed QCN?||Change name of listener from OracleDCNListener to OracleChangeNotificationListener.|
|3||How should a descriptor be configured to use database change notification?||New databaseChangeNotificationType on CachePolicy and @Cache.|
- Other databases and event mechanisms.
- Show example the uses triggers and Oracle AQ.