Patterns of Distributed Systems

Chapter 23

Hybrid Clock

Use a combination of system timestamp and logical timestamp to have versions as date and time, which can be ordered.

Problem

When Lamport Clock is used as a version in Versioned Value, clients do not know the actual date-time when the particular versions are stored. It’s more convenient for clients to access versions using date and time like 01–01–2020 instead of an integer like 1, 2, 3.

Solution

Hybrid logical clock [Demirbas2014] provides a way to have a version which is monotonically increasing just like a simple integer, but also has relation to the actual date and time. Hybrid clocks are used in practice by databases like MongoDB⁷⁷ or CockroachDB.⁷⁸

77. https://www.mongodb.com/blog/post/transactions-background-part-4-the-global-logical-clock ...