percona-playback is a utility for replaying database server load. It currently supports replaying load captured either via a MySQL slow query log file or from tcpdump capture of the MySQL network protocol.
Due to the highly parallel nature of most database server workloads, it is essentially impossible to ever 100% accurately replay what went on at any particular time. percona-playback makes a best effort to be accurate and attempts to inform you of how much the replay differed from what was originally executed.
You may get more inaccuracies when replaying against different database server versions or a database server running on different hardware. This could be due to how IO is scheduled, which competing transactions get row locks first etc etc.