It is an internal detail that prevents such a check in R_C. That internal detail is that I maintain a direct reference to the cached state. So if it changes (by another tx) I do not know this. Now with R_R, I do know this since I maintain a copy to the cached state. And I can check if my copy is still the same as what is cached, and this is how I can check for write skews. This copying is necessary for R_R (to provide consistency) but it is not necessary for R_C (since you always want to read committed state anyway). Adding this layer of copying just for the sake of write skew detection is an unnecessary overhead since the copy never will be used for anything else. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4223737#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...