Is there a performance penalty in executing read only queries under transaction?

It depends on what underlying transaction manager you are using. The default spring "transaction per thread, no XA transactions" probably doesn't have a any penalty. If you are using JBoss with the XA transaction manager, then it will write some data to a transaction log .

Theoretically there's a performance penality to adding AOP (and thus introspection/reflection) overhead to more methods than necessary. Also there's the added overhead of opening and closing more transactions than needed. It should be up to the developer coding the data-acces layer to know when and if a transaction should be started IMHO.

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