Courses/Distributed Systems

Distributed Systems

CS3.401

Prof. Kishore Kothapalli•Monsoon 2025-26•4 credits

Revision Notes/Unit 3 — Global Snapshots

Unit 3 — Global Snapshots

Recording a consistent snapshot of a distributed system without stopping it. The C1/C2 cut conditions. Chandy-Lamport (FIFO channels), Lai-Yang (non-FIFO, white/red colouring), Acharya-Badrinath (causal channels, 2N messages). Banking example showing inconsistent vs consistent cuts.

Chandy-Lamport, Lai-Yang, Acharya-Badrinath + Consistent Cuts

16 min

We can't freeze time across a distributed system to take a snapshot. Instead, each process records its own local state independently, and the algorithm records the in-transit messages on each channel such that the combined picture is one the system *could have been in* in an equivalent execution — even if it wasn't actually in that exact state at any single instant. The channel-type assumption (FIFO / non-FIFO / causal) determines which algorithm applies.