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POHibernate, @SequenceGenerator and allocationSize
 

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    <p>We all know the default behaviour of Hibernate when using <code>@SequenceGenerator</code> - it increases real database sequence by <strong>one</strong>, multiple this value by 50 (default <code>allocationSize</code> value) - and then uses this value as entity ID.</p> <p>This is incorrect behaviour and conflicts with <a href="http://docs.oracle.com/javaee/5/api/javax/persistence/SequenceGenerator.html">specification</a> which says:</p> <blockquote> <p>allocationSize - (Optional) The amount to increment by when allocating sequence numbers from the sequence.</p> </blockquote> <p>To be clear: I do not bother about gaps between generated IDs.</p> <p>I care about IDs that are <strong>not consistent</strong> with underlying database sequence. For example: any other application (that e.g. uses plain JDBC) may want to insert new rows under IDs obtained from sequence - but all those values may be already used by Hibernate! Madness.</p> <p>Do somebody know any solution to this problem (without setting <code>allocationSize=1</code> and thus degrading performance)?</p> <p><strong>EDIT:</strong><br> To make things clear. If last inserted record had ID = <code>1</code>, then HB use values <code>51, 52, 53...</code> for its new entities BUT at the same time: sequence's value in database will be set to <code>2</code>. Which can easily leads to errors when other applications are using that sequence. <br/></p> <p>On the othe hand: specification says (in my understanding) that database sequence should have been set to <code>51</code> and in the meantime HB should use values from range <code>2, 3 ... 50</code></p> <p><br/><strong>UPDATE:</strong> <br/> As Steve Ebersole mentioned below: the behaviour described by me (and also the most intuitive for many) can be enabled by setting <code>hibernate.id.new_generator_mappings=true</code>.</p> <p>Thanks all of You.</p> <p><strong>UPDATE 2:</strong><br> For future readers, below you can find a working example.</p> <pre><code>@Entity @Table(name = "users") public class User { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "USERS_SEQ") @SequenceGenerator(name = "USERS_SEQ", sequenceName = "SEQUENCE_USERS") private Long id; } </code></pre> <p>persistence.xml</p> <pre><code>&lt;persistence-unit name="testPU"&gt; &lt;properties&gt; &lt;property name="hibernate.id.new_generator_mappings" value="true" /&gt; &lt;/properties&gt; &lt;/persistence-unit&gt; </code></pre>
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    1. CO"without setting allocationSize=1 and thus degrading performanc" why it degrade performance is you set it to 1?
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    2. CO@sheidaei see may comment below :-) This is because every `save` needs to query database for next value of the sequence.
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