Leslie Lamport

Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works Leslie Lamport Bakery Time, Clocks, and the Ordering of Events Byzantine Generals Problem Distributed Snapshots Jenny Tyrv¨ainen LATEX Temporal Logic of Actions The algorithm Conclusion April 20, 2016 Leslie Lamport Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals Problem Distributed Snapshots LATEX Temporal Logic of Actions The Paxos algorithm Conclusion

Born February 7 1941 in Leslie Lamport

Jenny Tyrv¨ainen

Introduction

Education and I Mathematician by his education Career

Most important works I Has worked in industry, not an academic Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals Problem I Fields: concurrency and distributed systems Distributed Snapshots LATEX Temporal Logic of Actions I Lists 180 publications and other texts at his home page The Paxos algorithm Conclusion

I Several awards and honors (IEEE John von Neumann Medal 2008) Education and Career Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career I BSc at MIT 1960 Most important works Bakery algorithm Time, Clocks, and the I MSc at 1963 Ordering of Events Byzantine Generals Problem Distributed Snapshots LATEX I Mitre Corporation 1962-1965 Temporal Logic of Actions The Paxos algorithm Conclusion I Marlboro College 1965-1969

I Massachusetts Computer Associates (Compass) 1970-1977 Education and Career continues Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important PhD at Brandeis University 1972: The Analytic Cauchy works I Bakery algorithm Time, Clocks, and the Problem with Singular Data Ordering of Events Byzantine Generals Problem Distributed Snapshots I SRI International 1977-1985 LATEX Temporal Logic of Actions The Paxos algorithm I Digital Equipment Corporation / 1985-2001 Conclusion

I 2001 - Bakery algorithm, 1974 () Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important I Works as queue ticket dispencers at bakery etc. works Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals I Each process chooses own queue number by asking Problem Distributed Snapshots around and choosing a larger number LATEX Temporal Logic of Actions The Paxos algorithm I If same number, process number decides Conclusion

I Enters critical section on turn, smallest number first Leslie Lamport

Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works I Solves mutual exclusion problem! Doesn’t rely on lower Bakery algorithm Time, Clocks, and the Ordering of Events level Byzantine Generals Problem Distributed Snapshots I Process can read all memory, write only its own: LATEX Temporal Logic of simultaneous read and write ok Actions The Paxos algorithm I Process can read arbitrary value Conclusion Time, Clocks, and the Ordering of Events, 1978 Leslie Lamport Jenny Tyrv¨ainen

Introduction

I The Maintenance of Duplicate Databases by Paul Education and Career

Johnson and Bob Thomas Most important works Bakery algorithm Time, Clocks, and the I Ordering of events: Two observers can disagree, which Ordering of Events Byzantine Generals event happened first Problem Distributed Snapshots LATEX Temporal Logic of Actions I Synchronization of logical clocks to achieve partial The Paxos algorithm ordering Conclusion

I Expand to total ordering → state-machine for arbitrary distributed system

I PODC Influential Paper Award 2000 and ACM SIGOPS Hall of Fame Award 2007 Leslie Lamport

Clock conditions: Jenny Tyrv¨ainen Introduction I C1. If a and b events in Pi , and a comes before b, Education and Ci (a) < Ci (b) Career Most important I C2. If a: Pi sends a message and b is Pj receiving it, works Bakery algorithm Ci (a) < Cj (b) Time, Clocks, and the Ordering of Events Byzantine Generals Implementation rules: Problem Distributed Snapshots LATEX I IR1. Each process increments its clock between two Temporal Logic of Actions successive events The Paxos algorithm Conclusion I IR2.

I (a) event a: send m by process then include timestamp with current clock value I (b) event b: receive m: process sets clock greater or equal to present value and greater than received timestamp The Byzantine Generals Problem, 1982 Leslie Lamport Jenny Tyrv¨ainen (consensus) Introduction

Education and Career

Most important I SIFT: Design and Analysis of a Fault-Tolerant works Bakery algorithm Computer for Aircraft Control, 1978 (Jean-Claude Time, Clocks, and the Ordering of Events Byzantine Generals Laprie Award in Dependable Computing 2014) Problem Distributed Snapshots LATEX I Reaching Agreement in the Presence of Faults, 1980 Temporal Logic of Actions (Edsger W. 2005) The Paxos algorithm Conclusion

I New paper mainly to assign a new name to the problem

I Jean-Claude Laprie Award in Dependable Computing 2013 The Problem Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works I Group of generals deciding on attack/retreat, need to Bakery algorithm Time, Clocks, and the Ordering of Events reach consensus Byzantine Generals Problem Distributed Snapshots LATEX I Some are traitors, trying to get loyal generals to adopt a Temporal Logic of Actions bad plan The Paxos algorithm Conclusion

I How many generals are needed to tolerate n traitors? The Solution Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals Solution with oral messages: 3n+1 generals Problem I Distributed Snapshots LATEX Temporal Logic of Actions The Paxos algorithm I With signatures: 2n+1 generals Conclusion Leslie Lamport

Jenny Tyrv¨ainen

Introduction OM(0): Education and Career (1) Commander sends value to every lieutenant Most important (2) Each lieutenant: use the value received or works Bakery algorithm RETREAT, if no value Time, Clocks, and the Ordering of Events Byzantine Generals Problem OM(m), m > 0: Distributed Snapshots LATEX Temporal Logic of if no value received, use RETREAT Actions (1) Commander sends value to every lieutenant The Paxos algorithm Conclusion (2) every lieutenant uses OM(m-1) to send received value to n-2 other lieutenants (3) from received values, select majority Distributed Snapshots: Determining Global Leslie Lamport Jenny Tyrv¨ainen States of a Distributed System, 1985 Introduction Observer process: Education and Career save state, send a token to all others Most important works Bakery algorithm Process on receiving token: Time, Clocks, and the Ordering of Events Byzantine Generals save state, send to observer Problem send token on every subsequent message Distributed Snapshots LATEX Temporal Logic of Actions If a process receives a message without the token, forward to The Paxos algorithm observer Conclusion

The observer builds the global state

I ACM SIGOPS Hall of Fame Award 2013 and Edsger W. Dijkstra Prize in 2014 LAT X: A Document Preparation System, 1986 Leslie Lamport E Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works I Macro package to ’s TEX Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals Problem Distributed Snapshots I For writing the Great American Concurrency book LATEX Temporal Logic of (didn’t) Actions The Paxos algorithm Conclusion

I A user manual, published by Addison-Wesley Temporal Logic of Actions (TLA), 1994 Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important I Formalism for describing concurrent systems works Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals I ”If you’re not writing a program, don’t use a Problem Distributed Snapshots programming language” LATEX Temporal Logic of Actions The Paxos algorithm I Developed also TLA+ and PlusCal → TLA IDE Conclusion

I Logic, algorithm language and tools for mechanically checking proofs TLA Example Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals Problem Distributed Snapshots LATEX Temporal Logic of Actions The Paxos algorithm Conclusion

https://upload.wikimedia.org/wikipedia/commons/9/98/TLA IDE screenshot.png The Part-Time Parliament, 1998 Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career I Tried to prove, that it is impossible to maintain Most important works consistency despite any number of non-Byzantine faults Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals Problem I Paxos algorithm instead Distributed Snapshots LATEX Temporal Logic of Actions The Paxos algorithm I Tried to popularize like the Byzantine generals problem Conclusion

I ACM SIGOPS Hall of Fame Award 2012 Paxos algorithm Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important I The consensus algorithm: synod works Bakery algorithm Time, Clocks, and the Ordering of Events I Three-phase: Byzantine Generals Problem first value proposed, then accepted and lastly learned Distributed Snapshots LATEX Temporal Logic of Actions The Paxos algorithm I Client-server model, server duplicated: described as Conclusion deterministic state-machine

I Fault-tolerance against arbitrary faults Conclusion Leslie Lamport Jenny Tyrv¨ainen

Introduction

I Enormous impact on the development of distributed Education and systems Career Most important works Bakery algorithm I Developed many methods and concepts now considered Time, Clocks, and the Ordering of Events Byzantine Generals elemental Problem Distributed Snapshots LATEX Temporal Logic of I Mathematics to : Actions The Paxos algorithm I Formal descriptions Conclusion

I Proofs for concurrency

I IEEE John von Neumann medal: ”For establishment of the foundations of distributed and ” Thank you! Leslie Lamport Jenny Tyrv¨ainen

Introduction

Education and Career

Most important works Bakery algorithm Time, Clocks, and the Ordering of Events Byzantine Generals Problem Distributed Snapshots LATEX Questions? Temporal Logic of Actions The Paxos algorithm Conclusion