Distributed Systems

Computers can sometimes be unexpectedly tricky. Having them accomplish seemingly rudimentary tasks can be a lot more complicated than we would expect. One example is having a group of them decide and come to an agreement upon something: a process known as consensus. That something could be anything. It could be what time of the day they should begin their attack to take over the world. Or simply the amount in your bank account at some given moment: Without agreement that amount may be $10 according to your work pc while your laptop at home says $100. Let’s elaborate on the former scenario as it’s more likely to happen. Say we have three machines that we call X, Y and Z plotting to conquer the world on a Monday. They have an plan of attack that only works if all available computers show up to battle and no one stays behind. A number of things can go wrong while they’re trying to come to an agreement on what time to begin their attack. One fundamental problem arises because everyone has an opinion. Computer X maybe suggests 08:00 for the takeover since it’s monday morning and the humans are still hungover from the weekend while some other computer Z thinks 13:00 is better because, well, Z’s not really a morning computer. Having them agree on a time is crucial as the humans have a better chance if all computers don’t show up. Another issue is that these computers are located in different parts of the world, communicating via cables and whatnot. If X suggests 08:00, it has to be sure that the suggestion reaches Y and Z as long as they are alive so as not to end up alone on the battlefront. ...