I'm using Postgre with Hibernate but when i try to insert many records in database its very slow.
10.000 inserts takes more than half a minute.
In hibernate.cfg i set up <property name="hibernate.jdbc.batch_size">100</property>
I'm using the following code from the book java persistance with hibernate:

JDBC-batch insert is ineffective when using native id generator.
Do you use native id generator on your User entity?

This is the code from .hbm file

<id name="userId" column="user_id">
<generator class="sequence">
<param name="sequence">user_id_sequence</param>
</generator>
</id>

In first line I would check with following code if your jdbc-driver is supporting BatchUpdates at all.
(not all drivers do effectively implements this feature).



Anyway I guess that the bottleneck is the database itself.
Create some stack with jstack during the half minute the application is running.
Then look at the stacktraces you got.
If the stacks are almost always executing in socketRead or socketWrite,
then it is effectively the database (or a extremely slow network) which is the bottleneck.

Did you try looking at the SQL your code generates? I suspect Hibernate is allocating a sequence id from database before every insert.
Check this link for an explanation: http://korhner.github.io/hibernate/hibernate-performance-traps-part-3/