11/02/2011
TimeKeeper’s advanced algorithms can compensate for virtual machine difficulties in keeping accurate time.
The problem with a virtual machine as far as time synchronization goes is that the VM will suspend for seconds at a time while the underlying operating systems work on something else. As it becomes more common to migrate virtual machines within a cluster or even a larger data center in order to load balance, this problem gets worse. A VM waking up after say 5 seconds has passed will detect a huge gap between its current time and the time provided by the clock. After a day or two, it’s not unusual to see a VM that is seconds out of sync. But a VM running TimeKeeper will smoothly recover its footing rapidly and smoothly as the smoothing algorithms TK uses to compensate for network packet delays and oscillator variation produce a quick convergence with a time source. You can hook a VM running timekeeper up to an NTP source and expect pretty good time tracking. This is not something we were initially targeting - for financial trading software the random delays of VMs are not acceptable - but it’s an interesting side effect. If VMs are being used for large scale database processing or map-reduce, the stability of a TK validated timestamp may improve data reliability and also reduce locking overhead.