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Selective Anti-Entropy. Weibin Zhao Henning Schulzrinne {zwb,hgs}@cs.columbia.edu Internet Real-Time Laboratory Columbia University. Introduction. Anti-Entropy Asynchronous replication, eventual consistency Peer-wise session Exchange differences, summary vector

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selective anti entropy

Selective Anti-Entropy

Weibin Zhao

Henning Schulzrinne

{zwb,hgs}@cs.columbia.edu

Internet Real-Time Laboratory

Columbia University

introduction
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
approach
Approach
  • Subsets of updates
    • Rx: all updates initially received by Rx
    • Θ(Rx, {Rx1, Rx2, …, Rxk}, Rz): SAE request
    • Only specified subsets are solicited
  • SAE types
    • Select-one-direct: Θ(Rx, {Rz}, Rz)
    • Select-one-indirect: Θ(Rx, {Ry}, Rz)
    • Select-multiple: Θ(Rx, {Ry, Rz}, Rz)
    • Select-all: = CAE
example sae vs cae
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}

Θ(R1,{R2},R2)

Θ(R1,{R3},R3)

R1 {a,b,c,d}

R1

parallel sae sessions
Parallel SAE Sessions
  • All select-one-direct sessions
  • In general, Rx can run kSAE 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
multi scope partial replication
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)

summary problem
Summary Problem

(2)

  • 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

b?

(3)

(1)

R6(S1,S2)

R6 states (t1<t2<t3)

safe sae sessions
Safe SAE Sessions
  • select-one-direct: Θ(Rx, {Rz}, Rz)
    • Safe for all
  • select-one-indirect: Θ(Rx, {Ry}, Rz)
    • Safe if S(Rx)  S(Ry)  S(Rz)
    • Safe: Θ(R3, {R1}, R6)

S(R3)  S(R1) = {S1, S2} = S(R6)

    • Unsafe: Θ(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)

conclusions
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