hlc: a hybrid physical/logical clock package for Go

[Jason E. Aten]

I have open sourced my hybrid physical/logical clock package, here.

https://github.com/glycerine/hlc

HLC are useful for solving various problems in distributed systems.

The concept of an HLC was invented in this 2014 paper, to combine and preserve the convenient features of both physical and logical clocks:

"Logical Physical Clocks and Consistent Snapshots in Globally Distributed Databases" by Sandeep Kulkarni, Murat Demirbas, Deepak Madeppa, Bharadwaj Avva, and Marcelo Leone.

https://cse.buffalo.edu/tech-reports/2014-04.pdf

See for instance their use in CockroachDB and MongoDB as alternatives to Spanner's TrueTime approach when atomic clocks are unavailable.

https://cse.buffalo.edu/~demirbas/publications/augmentedTime.pdf

https://github.com/AugmentedTimeProject/AugmentedTimeProject

https://muratbuffalo.blogspot.com/2025/01/use-of-time-in-distributed-databases.html

Enjoy,

Jason

[Michael Oguidan]

Thank you very much

[roger peppe]

This looks potentially useful, thanks.

One thing I'd pick up from the README, which says:

> The Go standard library time package does not provide a user-accessible monotonic clock.

That might have been true at one point, but is no longer the case.

See https://go.googlesource.com/proposal/+/master/design/12914-monotonic.md for details of the

monotonic clock proposal.

In short, time.Time.Sub on timestamps derived from time.Now will give the monotonic time interval

between them, regardless of leap seconds and the like.

So:

    t0 := time.Now()

    t1 := time.Now()

    d := t1.Sub(t0)

will guarantee that d is non-negative (assuming the underlying system provides access to a monotonic clock).

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[Jason E. Aten]

Hi Rog,

Yes, I am aware of that feature, but that does not expose an actual monotonic

timestamp reading to the user, and so I stand by

my claim that the Go runtime does not expose a monotonic 

clock to the user (like the hlc package provides).

https://go.googlesource.com/proposal/+/master/design/12914-monotonic.md lets you

take the difference of two local timestamps, but does not give an absolute time reading

that would correspond to any actual "time of day".

So I still see hlc as valuable for that otherwise un-addressed use case.

- Jason