Access intent policies
An access intent policy is a named set of properties or access intents that govern data access for EJBs persistence. We can assign policies to an entity bean and to individual methods on an entity bean's home, remote, or local interfaces during assembly. We can set access intents only within EJB V2.x-compliant and later modules for entity beans with CMP V2.x.
This product supplies a number of access intent policies that specify permutations of read intent and concurrency control; the pessimistic and update policy can be qualified further. The selected policy determines the appropriate isolation level and locking strategy used by the run time environment.
For transitioning users: Access intent policies are specifically designed to supplement the use of isolation level and access intent method-level modifiers found in the extended deployment descriptor for EJB version 1.1 enterprise beans. We cannot specify isolation level and read-only modifiers for EJB version 2.x and later enterprise beans.trns
Access intent policies configured on an entity basis define the default access intent for that entity. The default access intent controls the entity unless you specify a different access intent policy based on either method-level configuration or application profiling.
Deprecated feature: Method level access intents were deprecated in V6.x. depfeat
Use application profiling or method level access intent policies to control access intent more precisely. Method-level access intent policies are named and defined at the module level. A module can have one or many policies. Policies are assigned, and apply, to individual methods of the declared interfaces of entity beans and their associated home interfaces. A method-based policy is acted upon by the combination of the EJB container and persistence manager when the method causes the entity to load.
For entity beans that are backed by tables with nullable columns, use an optimistic policy with caution. The top down default mapping excludes nullable fields. We can override this when doing a meet-in-the-middle mapping. The fields used in overqualified updates are specified in the ejb-rdb mapping. If nullable columns are selected as overqualified columns, partial update should also be selected.
When using DB2 for z/OS Version 8, nullable OCC columns create no problems. This is true for JDBC and SQLJ deploy options, and partial and full update.
An entity configured with a read-only policy that causes a bean to be activated can cause problems if updates are attempted within the same transaction. Those changes are not committed, and the process displays an exception because data integrity might be compromised.
Subtopics
Concurrency control
Read-ahead hints
Database deadlocks caused by lock upgrades
Access intent assembly settings
Related tasks
Use access intent policies
Related
Access intent -- isolation levels and update locks
Access intent exceptions