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One of the most surprising and inspired facets of Spanner is its use of atomic clocks and GPS clocks to give participating nodes really accurate wall time synchronization. The designers of Spanner call this "TrueTime", and it provides a tight bound on clock offset between any two nodes in the system.AK
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The underlying time references used by TrueTime are GPS and atomic clocks.AK
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TrueTime is implemented by a set of time master machines per datacenter and a
timeslave daemon per machine. The majority of masters have GPS receivers with
dedicated antennas; these masters are separated physically to reduce the effects of
antenna failures, radio interference, and spoofing. The remaining masters (which we
refer to as Armageddon masters) are equipped with atomic clocks. An atomic clock is
not that expensive: the cost of an Armageddon master is of the same order as that of a
GPS master.
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select_val jump_on_val которая просто делает jump на нужный вариантPG