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copied!<pre><code>public Long getNewInvoiceNumber() { Criteria crit = getSession().createCriteria(Numbers.class); crit.setLockMode(LockMode.PESSIMISTIC_WRITE); // LINE ADDED Numbers n = ((Numbers)crit.uniqueResult()); Long newNumber = n.getInvoiceNumber() + 1L; n.setInvoiceNumber(newNumber); getSession().update(n); // LINE ADDED return newNumber; } </code></pre> <p>You must use InnoDB if using MySQL, you should ensure Hibernate is adding the "FOR UPDATE" to the SQL generated for the <code>crit.uniqueResult()</code> part. I would also set a Java breakpoint just after (to stop execution) and manually test the same SQL query causes another client to block.</p> <p>This is more to test your SQL server is sane and your Dialect is setup correctly and basically the feature works for you.</p> <p>This forces serialization at the SQL server in the generation of the next InvoiceNumber.</p> <p>This way you never get 2 InvoiceNumber the same even if 1000 users simultaneously try to make invoices.</p> <p>NOTE: LockOptions replaces the LockMode to specify mode things about this aspect of concurrency. See the hibernate release notes for help.</p> <p>NOTE: You talked of transactions lasting minutes. While the transaction is not committed no other user can generate a new invoice number. Maybe you need to run this as a nested and separate transaction. Then you have the problem holes appearing in InvoiceNumber's if there is a failure to use the number due to some other processing error. Accountants / accounting systems don't like holes in invoice numbers, nor them being out of date sequence.</p> <p>Related MySQL documentation link <a href="https://dev.mysql.com/doc/refman/5.0/en/innodb-locking-reads.html" rel="nofollow">https://dev.mysql.com/doc/refman/5.0/en/innodb-locking-reads.html</a></p>

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