You could try 'NotSupported' as your session bean transaction attribute.
Thanks for your answer.
I try "NotSupported" as my session bean transaction attribute for the readOnly() method, but I've always the same trouble :
[EntityBeanName] LOCKING-WAITING (TRANSACTION) for id EntityBeanNamePK@1e8 ctx.hash 2025737 tx:TransactionImpl:XidImpl [FormatId=257, GlobalId=internal.dvlpt.com//1285, BranchQual=]
Nevertheless, il seems to be more efficient because there is less transaction with "NotSupported" attribute than with "Required" attribute.