Paper describing Atomic Broadcast protocol that delivers messages in two message steps (fast) even in the presence of multiple concurrent broadcasts (collision-fast).

1. Collision-fast Atomic Broadcast
Rodrigo Schmidt (Facebook)
Lasaro Camargos (UFU)
Fernando Pedone (USI)

2. Consensus
Paxos

3. A
B
A
C
Proposers Learners
B
Acceptors
B
A
B
Consensus in a nutshell

4. Atomic Broadcast
A
B
A
C
Proposers Learners
B
ACB
ACB
B
ACB
ACB
ACB
ACB
CB
ACB
AC

5. From Consensus to ABCast
...
A
B
C
D
B
B D

6. Dealing with Collisions
A
B
C
D
Paxos

7. Collision Fast approaches:
limitations
• A single failure is supported
• All but one proposer are also acceptors
• Still have to retry
• Hiper-fast learning
single failure, acceptor in learners, or
learner + hyper-fast proposer is a quorum

8. M-Consensus
1 A
2 B
3 A
4 C
Proposers Learners
Acceptors
1:A,2:B,3:A,4:C1:A,2:B,3:A,4:⊥

9. M-Consensus: all good
1 A
2
3 C
Collision-Fast
Proposers
LearnersAcceptors
1 A
3 C
1st1 A1 A1 A1 A
3 C
2 ⊥2 ⊥2 ⊥
2nd
1A, 3C
1A, 3C
1A
1A, 3C1A, 3C
1A1A
3 C
1 A, 2⊥, 3 C

10. CFABcast
...
A
X
B
Z
C
Y
D
V
BDA XZCV Y

11. M-Consensus: failures
Collision-Fast
Proposers
LearnersAcceptors
3C
1 A
1 A, 3 C
Coordinator 1 A, 3 C, 2 ⊥
1 A
3C
1 A
1 A
3C
1 A
2⊥
3C
1 A
2⊥
3 C
1 A
2⊥
3C
1 A
2⊥
3C
1 A
2⊥
3 C
1 A
2⊥
3C

12. Mencius
• similar communication pattern in the
happy path
• conjecture: similar numbers
Why not use Mencius then?

13. Ours is trully collision fast
• Mencius is collision-fast until failures
happen
• failures affect all future instances
• reconfiguration vs reinstantiation
CFABcast recovers from failures instead of
working around them, at greater expense

14. Summary
CFABCast: a (trully) collistion-fast atomic
broadcast protocol
an Atomic Broadcast protocol that may
(always) deliver the messages of multiple
broadcasters within two communication
steps

15. Questions?
lasaro@facom.ufu.br
rodrigo@fb.com
fernando.pedone@usi.ch

16. Collision-fast Atomic Broadcast
Rodrigo Schmidt (Facebook)
Lasaro Camargos (UFU)
Fernando Pedone (USI)