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Firefly: Scalable, Ultra-Accurate Clock Synchronization for Datacenters#

OCP Global Summit 2025 digest Program Wildcard pick 13–16 October 2025

Abstract Recording

Speakers: Yuliang Li (Google)

Play the recording: Firefly: Scalable, Ultra-Accurate Clock Synchronization for Datacenters

  • Why: Sub-10ns device-to-device sync is two orders of magnitude past what PTP practice delivers, and the technique — consensus on a random overlay rather than a spanning tree — is a genuinely different way to solve time in a fabric. Cloud financial exchanges are the driver, but precise time increasingly matters for telemetry correlation and distributed debugging.
  • What: A software-driven datacenter clock sync system achieving sub-10ns device-to-device and ≤1µs device-to-UTC accuracy in a 248-machine Clos network, resilient to time server failure and unstable clocks. (from abstract only)
  • How: A distributed consensus algorithm over a random overlay graph converges devices to a common time with gradual hardware-clock adjustments; "layered synchronization" decouples internal (device-to-device) from external (UTC) sync so external jitter doesn't disturb internal consistency.
  • Where applicable: Software-only, demonstrated on a 248-machine Clos network — no special hardware claimed. Google research system; results are from that testbed, so hyperscale behavior is inferred rather than shown.