You must use a stateless session first. Instead of calling OpenSession (); (in a factory session) you call OpenStatelessSession (); It has the same api as a regular session, but there is no caching and more (much faster for bulk data operations). Then you need to set the batch size by calling .AdoNetBatchSize ([[batch size]]); where you install the database in your configuration.
This can do the trick. But you should know that this is not a relay for which nhibernate (or any other orm) is created, so do not count on any performance.
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