1. A method of controlling a coalescing of outermost memory transactions, the coalescing causing committing of memory store data to memory for a first transaction to be done at transaction execution (TX) end of a second transaction, the method comprising: executing, by a processor, a run-time instrumentation program for monitoring and modifying an associated program having a plurality of transactions; initiating, by the processor, execution of the associated program; based on execution of transactions, by the processor, of the associated program, the run-time instrumentation program dynamically obtaining instrumentation information associated with the execution; and based on the obtained instrumentation information, dynamically modifying, by the processor, continued execution of transactions of the associated program to optimize transactional execution (TX) by adding a coalescing instruction that controls, at least in part, a coalescing of one or more outermost transactions, wherein the run-time instrumentation program modifying the continued execution of the associated program includes adding one or more coalescing instructions to the associated program to control coalescing of one or more of the plurality of transactions based, at least in part, on an analysis of gathered instrumentation information.