Selective Anti-Entropy

1
Selective Anti-Entropy

• Weibin Zhao
• Henning Schulzrinne
• zwb,hgs_at_cs.columbia.edu
• Internet Real-Time Laboratory
• Columbia University

2
Introduction

• Anti-Entropy
• Asynchronous replication, eventual consistency
• Peer-wise session
• Exchange differences, summary vector
• Complete anti-entropy (CAE)
• Reconcile all inconsistent states
• Selective anti-entropy (SAE)
• Selectively reconcile inconsistent states

3
Approach

• Subsets of updates
• Rx all updates initially received by Rx
• T(Rx, Rx1, Rx2, , Rxk, Rz) SAE request
• Only specified subsets are solicited
• SAE types
• Select-one-direct T(Rx, Rz, Rz)
• Select-one-indirect T(Rx, Ry, Rz)
• Select-multiple T(Rx, Ry, Rz, Rz)
• Select-all CAE

4
Example SAE vs. CAE

• R2 a,b, R3 c,d

CAE
R2 a,b,c
R3 a,c,d
d
a,b,c
R1
R1 a,b,c
R1 a,b,c,d
R2 a,b,c
R3 a,c,d
SAE
a,b
c,d
T(R1,R2,R2)
T(R1,R3,R3)
R1 a,b,c,d
R1
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Parallel SAE Sessions

• All select-one-direct sessions
• In general, Rx can run k SAE sessions s1,
  s2, , sk in parallel if update subsets u1,
  u2, , uk do not overlap,
  i.e., u1 ? u2 ? ? uk ?
• Example
• if u1 R2, R4, u2 R3, R5,
  then R1 can run s1 and s2 in parallel

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Multi-Scope Partial Replication

• State set divided into subsets scopes
• Applications directory services
• SLP directories scopes
• UDDI registries classifications

R1(S1,S2,S3)
R2(S1)
R3(S1,S2)
R4(S2,S3)
R5(S3)
R6(S1,S2)
R7(S3)
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Summary Problem
(2)
State Scope ID
a S1 (R6, t1)
b S2 (R6, t2)
c S1 (R6, t3)

• Solution space
• Summary vector replica, full replication
• Summary matrix replica scope, partial
  replication
• SAE summary vector replica, partial replication

R2(S1)
R3(S1,S2)
a,c
a,c
(3)
b?
(1)
R6(S1,S2)
R6 states (t1ltt2ltt3)
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Safe SAE Sessions

• select-one-direct T(Rx, Rz, Rz)
• Safe for all
• select-one-indirect T(Rx, Ry, Rz)
• Safe if S(Rx) ? S(Ry) ? S(Rz)
• Safe T(R3, R1, R6)
• S(R3) ? S(R1) S1, S2 S(R6)
• Unsafe T(R3, R6, R2)
• S(R3) ? S(R6) S1, S2 ? S(R2) S1
• select-multiple or select-all
• Safe if all select-one-indirect sessions are safe

R1(S1,S2,S3)
R2(S1)
R3(S1,S2)
R6(S1,S2)
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Conclusions

• Advantages of SAE
• Generalize CAE select-all CAE
• Fine control of received subsets of updates
• Perform multiple SAE sessions in parallel
• Support multi-scope partial replication
  efficiently
• Prerequisite of SAE
• membership information of the replica set
• Generic Anti-entropy Request
• Anti-entropy type selective or complete
• Each entry lower upper bound timestamps