The JPA provides a relatively easy way to persist objects, however, there are certain cases that often require a deeper understanding of the consequences that can take place. In these two posts, Carol McDonald and Felipe Gaucho walk you through two such cases, JPA concurrency locking and JPA optimistic locking. Read Carol McDonald's post 'JPA 2.0 Concurrency and locking': http://weblogs.java.net/blog/caroljmcdonald/archive/2009/07/jpa_20_concurre.html Read Felipe Gaucho's post 'Don't break the optimistic locking': http://weblogs.java.net/blog/felipegaucho/archive/2009/08/dont_break_the.html