TrueTime
Google's globally-synchronised clock with a known uncertainty bound.
Origin
Introduced in the Spanner paper (Corbett et al., OSDI 2012). Combines GPS receivers and atomic clocks at every datacenter to bound clock uncertainty to ~7ms.
Where it shows up in production
- Google Spanner Transactions "commit-wait" until the uncertainty window passes — buying externally-consistent global timestamps.
- CockroachDB HLC Hybrid Logical Clocks approximate TrueTime semantics without atomic hardware.
On Semicolony
Sources & further reading
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