A computer system includes multiple processing threads that execute in parallel. The multiple processing threads have access to a global environment including different types of metadata enabling the processing threads to carry out simultaneous execution depending on a currently selected type of lock mode. A mode controller monitoring the processing threads initiates switching from one type of lock mode to another depending on current operating conditions such as an amount of contention amongst the multiple processing threads to modify the shared data. The mode controller can switch from one lock mode another regardless of whether any of the multiple processes are in the midst of executing a respective transaction. A most efficient lock mode can be selected to carry out the parallel transactions. In certain cases, switching of lock modes causes one or more of the processing threads to abort and retry a respective transaction according to the new mode.