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Vector clock algorithm:

• Initially all clocks are zero.
• Each time a process experiences an internal event, it increments its own logical clock in the vector by one (inc()).
• Each time a process sends a message, it increments its own logical clock in the vector by one and then sends a copy of its own vector.
• Each time a process receives a message, it increments its own logical clock in the vector by one and updates each element in its vector by taking the maximum of the value in its own vector clock and the value in the vector in the received message (merge()).

The package provides the following immutable vector clock operations, where vector clocks are plain JS objects:

• inc(clock, id) - increment (or create) clock component
• remove(clock, id) - remove clock component
• merge(a, b) - merge two vector clocks
• signedSkew(a, b) - max signed difference between vector clocks
• absSkew(a, b) - max unsigned difference between vector clocks
• compare(a, b) - comparator for logically ordering vector clocks
• isBefore(a, b) - true if a < b
• isAfter(a, b) - true if a > b
• isConcurrent(a, b) - if both clocks represent concurrent updates
• equiv(a, b) - equality predicate
• orderAsc(a, b) - alias for compare()
• orderDesc(a, b) - reverse order to orderAsc()

References:

• Wikipedia
• Princeton COS 418: Distributed Systems
  • Lecture 4
  • Lecture 5
• F. Mattern: Virtual Time and Global States of Distributed Systems
• P. Krzyzanowski: Clock synchronization
• L. Lamport
• Akka docs

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