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Java Persistence API (JPA) Extensions Reference for EclipseLink, Release 2.4
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@Partitioned

Use @Partitioned to specify a partitioning policy to use for an Entity or relationship.


Annotation Elements

Table 2-47 describes this annotation's elements.

Table 2-47 @Partitioned Annotation Elements

Annotation Element Description Default

value

(Required) Name of the partitioning policy.




Usage

Use partitioning to partition the data for a class across multiple databases or a database cluster (such as Oracle RAC). Partitioning can provide improved scalability by allowing multiple database machines to service requests.

You can specify @Partitioned on an Entity, relationship, query, or session/persistence unit.

Partitioning Policies

To configure data partitioning, use the @Partitioned annotation and one or more partitioning policy annotations. The annotations for defining the different kinds of policies are:

Partitioning policies are globally-named objects in a persistence unit and are reusable across multiple descriptors or queries. This improves the usability of the configuration, specifically with JPA annotations and XML.

The persistence unit properties support adding named connection pools in addition to the existing configuration for read/write/sequence. A named connection pool must be defined for each node in the database cluster.

If a transaction modifies data from multiple partitions, JTA should be used to ensure 2-phase commit of the data. An exclusive connection can also be configured in the EntityManager to ensure only a single node is used for a single transaction.

Clustered Databases and Oracle RAC

Some databases support clustering the database across multiple machines. Oracle RAC allows for a single database to span multiple different server nodes. Oracle RAC also supports table and node partitioning of data. A database cluster allows for any of the data to be accessed from any node in the cluster. However, it is generally it is more efficient to partition the data access to specific nodes, to reduce cross node communication.

EclipseLink partitioning can be used in conjunction with a clustered database to reduce cross node communication, and improve scalability.

To use partitioning with a database cluster to following is required:


Examples

Example 2-87 shows how to partition Employee data by location. The two primary sites, Ottawa and Toronto are each stored on a separate database. All other locations are stored on the default database. Project is range partitioned by its ID, as shown in Example 2-88. Each range of ID values are stored on a different database. The employee/project relationship is an example of a cross partition relationship. To allow the employees and projects to be stored on different databases a union policy is used and the join table is replicated to each database.

Example 2-87 Using Partitioning

@Entity
@IdClass(EmployeePK.class)
@UnionPartitioning(
        name="UnionPartitioningAllNodes",
        replicateWrites=true)
@ValuePartitioning(
        name="ValuePartitioningByLOCATION",
        partitionColumn=@Column(name="LOCATION"),
        unionUnpartitionableQueries=true,
        defaultConnectionPool="default",
        partitions={
            @ValuePartition(connectionPool="node2", value="Ottawa"),
            @ValuePartition(connectionPool="node3", value="Toronto")
        })
@Partitioned("ValuePartitioningByLOCATION")
public class Employee {
    @Id
    @Column(name = "EMP_ID")
    private Integer id;
 
    @Id
    private String location;
    ...
 
    @ManyToMany(cascade = { PERSIST, MERGE })
    @Partitioned("UnionPartitioningAllNodes")
    private Collection<Project> projects;
    ...
}

Example 2-88 Using @RangePartitioning

@Entity
@RangePartitioning(
        name="RangePartitioningByPROJ_ID",
        partitionColumn=@Column(name="PROJ_ID"),
        partitionValueType=Integer.class,
        unionUnpartitionableQueries=true,
        partitions={
            @RangePartition(connectionPool="default", startValue="0", endValue="1000"),
            @RangePartition(connectionPool="node2", startValue="1000", endValue="2000"),
            @RangePartition(connectionPool="node3", startValue="2000")
        })
@Partitioned("RangePartitioningByPROJ_ID")
public class Project {
    @Id
    @Column(name="PROJ_ID")
    private Integer id;
    ...
}


See Also

For more information, see:

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