If you become familiar with Show trans output, you can determine if excessive time is spent in a general feature area or if a specific transaction is taking a longer than average time to execute.
Over that period, the averagetime to complete a job has dropped from 634 seconds to 395 seconds, while the output of MapReduce tasks has risen from 193 terabytes to 14,018 terabytes, Dean said.
Some experiments prove that the approach can not only improve the system's performance, but also decrease the average latency time of tuples and improve the output rate of tuples greatly.