Lamport Time Clocks

David Murray presented Leslie Lamport's, Time Clocks paper (ACM July 1978) The concept of one event happening before another in a distributed system is examined, and is shown to define a partial ordering of the events. A distributed algorithm is given for synchronizing a system of logical clocks which can be used to totally order the events. The use of the total ordering is illustrated with a method for solving synchronization problems. The algorithm is then specialized for synchronizing physical clocks, and a bound is derived on how far out of synchrony the clocks can become. Here is the live link

The novel notion Lamport introduced was Logical Clocks rather than physical server clocks. From herein we have the basis for ordering services in modern distributed systems.

Key takeaways, the ordering service feeds into a consensus machine, from here we have the framework for Raft, Paxos, blockchain and hand wavy sub systems such as commenting and messaging in social media systems.

Q&A - AFAIK business systems with aggregates from trees (bills-of-materials) have avoided distributed systems for centralized SQL systems? - Yes, central systems are simpler. There is some movement toward leader based systems, where a leader node is always in control. Although the leader node can change. The previous leader node then becomes a back-up node. There is often many back-up nodes. Zookeeper is a good example.

Peter Alvaro The trick (imo) is deciding when we can safely delegate consensus to the subtrees without going through the root, even when you make consensus hierarchical. Camille Fournier has a great talk about hierarchical zookeeper A , B , C // ToDo Trevor Menagh Oh, that's awesome. I really enjoy her work. The Manager's Path has been a lifesaver for me. Eric Hopper The spelling of the Swirld is, well, "Swirld" . Trevor Menagh (also see the Bakery Algorithm talk) talk Thanks for discussing leader systems in context of SQL and commentary

YOUTUBE 8tI1_KlO6xI The time has nothing to show because Time won't give me time and Time makes [servers] feel like they've got something real.