When in a multiMaster cluster, when setting connection.setReadOnly(XXX), if database allow it, a SET SESSION TRANSACTION READ ONLY / READ WRITE depending on the XXX value will be executed.

That's permit to assure never execute write query when in read only mode.
The downside of this is a query is executing every change of connection.setReadOnly() just to assure that.

A new option assureReadOnly can be created to tell if this can be avoid.