Logical Clocks(Distributed Systems)

Definition:

Logical Clocks are mechanisms used in distributed systems to establish a partial ordering of events across different nodes without relying on synchronized physical clocks. They assign timestamps to events to determine causality relationships between operations happening on different machines.

Example:

• Scenario: Three nodes (A, B, C) exchanging messages

Node A: [1] Send msg to B → [2] Receive from C → [4] Internal event
Node B: [3] Receive from A → [4] Send msg to C → [5] Internal event
Node C: [2] Send msg to A → [5] Receive from B → [6] Internal event

Lamport Clock Rules:

• Internal Events:

LC = LC + 1

• Send Message:

LC = LC + 1

• Receive Message:

LC = max(LC, received_timestamp) + 1