HashPartitioning (EclipseLink 2.7.15, API Reference)

```
@Target({TYPE,METHOD,FIELD})
@Retention(RUNTIME)
public @interface HashPartitioning
```
HashPartitioning partitions access to a database cluster by the hash of a field value from the object, such as the object's location, or tenant. The hash indexes into the list of connection pools. All write or read request for object's with that hash value are sent to the server. If a query does not include the field as a parameter, then it can either be sent to all server's and unioned, or left to the sesion's default behavior.
Partitioning can be enabled on an Entity, relationship, query, or session/persistence unit. Partition policies are globally named to allow reuse, the partitioning policy must also be set using the @Partitioned annotation to be used.

See Also:

Partitioned, HashPartitioningPolicy

Author:

James Sutherland

Since:

EclipseLink 2.2

Required Element Summary

Required Elements
Modifier and Type	Required Element	Description
`java.lang.String`	`name`	The name of the partition policy, names must be unique for the persistence unit.
`Column`	`partitionColumn`	The database column or query parameter to partition queries by.

Optional Element Summary

Optional Elements
Modifier and Type	Optional Element	Description
`java.lang.String[]`	`connectionPools`	List of connection pool names to partition across.
`boolean`	`unionUnpartitionableQueries`	Defines if queries that do not contain the partition field should be sent to every database and have the result unioned.

- Element Detail
  - name
```
java.lang.String name
```
    The name of the partition policy, names must be unique for the persistence unit.
- - partitionColumn
```
Column partitionColumn
```
    The database column or query parameter to partition queries by. This is the table column name, not the class attribute name. The column value must be included in the query and should normally be part of the object's Id. This can also be the name of a query parameter. If a query does not contain the field the query will not be partitioned.
- - connectionPools
```
java.lang.String[] connectionPools
```
    List of connection pool names to partition across. Defaults to all defined pools in the ServerSession.
    
    Default:
    
    {}
- - unionUnpartitionableQueries
```
boolean unionUnpartitionableQueries
```
    Defines if queries that do not contain the partition field should be sent to every database and have the result unioned.
    
    Default:
    
    false