1. Slides for Chapter 15: Replication
From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design
Edition 4, © Addison-Wesley 2005

2. Figure 15.1 A basic architectural model for the management of replicated dataFE
Requests and
replies C
Replica
Service
Clients
Front ends
managers RM
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

3. Figure 15.2 Services provided for process groups
Join
Group
address
expansion
Multicast
communication
send
Fail
Group membership
management
Leave
Process group
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

4. Figure 15.3 View-synchronous group communicationq r
p crashes
view (q, r)
view (p, q, r)
a (allowed).
b (allowed).
c (disallowed).
d (disallowed).
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

5. Figure 15.4 The passive (primary-backup) model for fault toleranceFE C RM
Primary
Backup
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

6. Figure 15.5 Active replicationFE C RM
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

7. Figure 15.6 Query and update operations in a gossip service
Val FE RM
Query,
prev
Val,
new
Update
Update,
Update id
Clients
gossip
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

8. Figure 15.7 Front ends propagate their timestamps whenever clients communicate directlyFE
Clients
Service
Vector
timestamps RM
gossip
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

9. Figure 15.8 A gossip replica manager, showing its main state components
Other replica
managers
Replica timestamp
Update log
Value
timestamp
Executed operation table
Stable
updates
Updates
Gossip
messages FE
Replica
Replica log
OperationID
Update
Prev
Replica manager
Timestamp table
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

10. Figure 15.9 Committed and tentative updates in BayoucN t0 t1 ti
Committed
Tentative t2
Tentative update ti becomes the next committed update
and is inserted after the last committed update cN.
ti+1
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

11. Figure 15.10 Transactions on replicated dataB A
Client + front end
getBalance(A)
Replica managers
deposit(B,3); U T
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

12. Figure 15.11 Available copiesX
Client + front end P B
Replica managers
deposit(A,3); U T
deposit(B,3);
getBalance(B)
getBalance(A) Y M N
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

13. Figure 15.12 Network partition
Client + front end B
withdraw(B, 4)
Replica managers
deposit(B,3); U T
Network
partition
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

14. Page 650 Gifford’s quorum concensus examples
Latency
Replica 1 75 75 75
(milliseconds)
Replica 2 65
100
750
Replica 3 65
750
750
Voting
Replica 1 1 2 1
configuration
Replica 2 1 1
Replica 3 1 1
Quorum R 1 2 1
sizes W 1 3 3
Derived performance of file suite:
Read
Latency 65 75 75
Blocking probability
0.01
0.0002
Write
Latency 75
100
750
Blocking probability
0.01
0.0101
0.03
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

15. Figure 15.13 Two network partitions
Replica managers
Network partition V X Y Z T
Transaction
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

16. Figure 15.14 Virtual partitionX V Y Z
Replica managers
Virtual partition
Network partition
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

17. Figure 15.15 Two overlapping virtual partitions
Virtual partition V 1 2 Y X V Z
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005

18. Figure 15.16 Creating a virtual partition
Phase 1:
• The initiator sends a Join request to each potential member. The argument of Join is a proposed logical timestamp for the new virtual partition.
• When a replica manager receives a Join request, it compares the proposed logical timestamp with that of its current virtual partition.
– If the proposed logical timestamp is greater it agrees to join and replies Yes;
– If it is less, it refuses to join and replies No.
Phase 2:
• If the initiator has received sufficient Yes replies to have read and write quora, it may complete the creation of the new virtual partition by sending a Confirmation message to the sites that agreed to join. The creation timestamp and list of actual members are sent as arguments.
• Replica managers receiving the Confirmation message join the new virtual partition and record its creation timestamp and list of actual members.
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn © Pearson Education 2005