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Difference between revisions of "EclipseLink/Examples/JPA/Locking"
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==How to Use EclipseLink Locking== | ==How to Use EclipseLink Locking== | ||
You can configure a descriptor with a locking policy that prevents one user writing over another user's work. | You can configure a descriptor with a locking policy that prevents one user writing over another user's work. | ||
− | *[[#Pessemistic Locking| | + | *[[#Pessemistic Locking|Pessimistic Locking]] |
*[[#Optimistic Locking|Optimistic Locking]] | *[[#Optimistic Locking|Optimistic Locking]] | ||
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'''''Optimistic Version Locking Example''''' | '''''Optimistic Version Locking Example''''' | ||
− | <source="java"> | + | <source lang="java"> |
@Entity | @Entity | ||
public class Empoyee implements Serializable { | public class Empoyee implements Serializable { |
Revision as of 16:00, 24 November 2009
Contents
How to Use EclipseLink Locking
You can configure a descriptor with a locking policy that prevents one user writing over another user's work.
Pessesmistic Locking
With pessimistic locking, the first user who accesses the data with the purpose of updating it locks the data until completing the update. The disadvantage of this approach is that it may lead to reduced concurrency and deadlocks.
See, PessimisticLocking
Optimistic Locking
With optimistic locking, all users have read access to the data. When a user attempts to write a change, the application checks to ensure the data has not changed since the user read the data.
By default, EclipseLink persistence provider assumes that the application is responsible for data consistency.
Version Locking
Optimistic version locking policies enforce optimistic locking by using a version field (also known as a write-lock field) that you provide in the reference class that EclipseLink updates each time an object change is committed.
Use the @Version
annotation to enable the JPA-managed optimistic locking by specifying the version field or property of an entity class that serves as its optimistic lock value (recommended).
EclipseLink provides the following version-based optimistic locking policies:
- VersionLockingPolicy: requires a numeric version field; EclipseLink updates the version field by incrementing its value by one.
- TimestampLockingPolicy: requires a timestamp version field; EclipseLink updates the version field by inserting a new timestamp (this policy can be configured to get the time from the data source or locally; by default, the policy gets the time from the data source).
Optimistic Version Locking Example
@Entity public class Empoyee implements Serializable { ... @Version @Column(name="OPTLOCK") protected int getVersionNum() { return versionNum; } ...
The field or property type must either be a numeric type (such as Number, long, int, BigDecimal, and so on), or a java.sql.Timestamp. We recommend using a numeric type.