Why not to use Increment generator type in clustered deployment environment?

[vaidehi agate]

Here is the small query:
I was going through a tutorial in which i found that Increment generator type should not be used in clustered deployment environment.
Can anybody tell me the reason behind the same?
Thanks

[Paul Sturrock]

Because the value is generated by Hibernate rather than the database. If you have multiple JVMs generating ids for the same entity you can't guarantee the value is unique.