Which annotation is used for implementing optimistic locking?

The annotation used for implementing optimistic locking is the @version annotation. Optimistic locking is a method to ensure that a database record is not modified by multiple transactions simultaneously, thereby preventing data inconsistencies. This approach is particularly useful in environments where conflicts are rare but can happen, ensuring that the application can handle concurrency without imposing heavy locks on database records.

When applying the @version annotation to an entity field, it indicates that this particular field will hold a version number or timestamp that gets incremented automatically whenever the record is updated. During an update operation, the application will check that the version number in the database matches the version number that was retrieved initially. If they do not match, it signifies that another transaction has updated the record since it was last read, and consequently, the current operation will fail, thus allowing the developer to handle the conflict appropriately.

Using @entity, @primaryKey, or @table annotations does not apply to the concept of optimistic locking. The @entity annotation identifies a class as a persistent entity representing a database table. The @primaryKey annotation denotes which field serves as the unique identifier for the entity. The @table annotation defines the name of the table associated with the entity. While these annotations are essential for defining the structure and