https://www.cockroachlabs.com/blog/living-without-atomic-clocks/ https://www.cockroachlabs.com/blog/living-without-atomic-clo... > perfectly synchronized clock

https://www.cockroachlabs.com/blog/living-without-atomic-clocks/ https://www.cockroachlabs.com/blog/living-without-atomic-clo... > perfectly synchronized clocks are a holy grail of sorts for distributed systems research. They provide, in essence, a means to absolutely order events, regardless of which node an event originated at two events that occur on two physically discrete nodes at exactly the same time have no well-defined order, even if their clocks are synchronized > before a node is allowed to report that a transaction has committed, it must wait 7ms. Because all clocks in the system are within 7ms of each other, waiting 7ms means that no subsequent transaction may commit at an earlier timestamp, even if the earlier transaction was committed on a node with a clock which was fast by the maximum 7ms. Pretty clever. so sending information between two antipodes on earth takes 66ms in one direction, 132ms round-trip, minimum. the speed of light dictates this lower limit if two transactions are made on those two nodes at exactly the same time, there is no objective order between the two. you can choose an order, but only with knowledge of both transactions, and that information physically cannot traverse space-time in 7ms so it's really not clear to me how this works. as an optimization, sure -- maybe there is some optimistic concurrency control that will fail transactions that conflict in the way i've described?