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# Failure Recovery of Overlay Tree-based Structures PowerPoint PPT Presentation

Doctoral Thesis. Failure Recovery of Overlay Tree-based Structures. Ing. Vladim í r Dynda Doc. RNDr. Ing. Petr Zem á nek, CSc. (supervisor). Czech Technical University in Prague Faculty of Electrical Engineering Department of Computer Science and Engineering. Agenda. Introduction

Failure Recovery of Overlay Tree-based Structures

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Doctoral Thesis

## Failure Recoveryof Overlay Tree-basedStructures

Doc. RNDr. Ing. Petr Zemánek, CSc.

(supervisor)

Czech Technical University in Prague

Faculty of Electrical Engineering

Department of Computer Science and Engineering

### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

### Introduction

• Problem statement

TR= (TM\FC, CE’ )

T4

T = (TM, CE)

TM

T5

CE

T6

T3

FC

T0

T2

S= (N, L)

T1

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Introduction

• Problem statement

• Failure recovery

• Reconnection ofT0, T1, ..., TN-1intoa restored network TR= (TM \FC, CE’)

• Correctness – TR is acyclic

• Completeness –TRcontains all the fragments

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Introduction

• Problem statement

• Environment

• Asynchronous distributed system

• No central authority / no global knowledge

• Unlimited sizes of S and T

• Arbitrary traffic directionin T

• Failures

• Node failures only

• Fail stop failure model

• Failures must not split S

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Introduction

• Goals of the thesis

• Proposal of a generic recovery platform

• Illustration of the tree restoration methods

• Simulation & verification of the theoretical properties

• Survey of possible applications

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Introduction

• State of the art

• On-demand / preplanned recovery

• Preplanned methods

• Employ pre-computed backup structures

• Existing preplanned methods

• Ancestor list (Yang-Fei, EFTMRP, HMTP)

• Secondary trees (Dual-tree, Coop-net)

• Link to random nodes (HMTP, Yoid)

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Introduction

• State of the art

• Weaknesses of the existing methods

• Poor scalability

• Restricted set of applicable trees

• Single points of failure

• Fixed level of fault tolerance

• Unrecoverable multiple failures

• Non-local restoration

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

6

### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

### BR Platform

• Bypass ring platform

• Ensures correctness and completeness

• Forms a basis for a tree reconnection

• Fabric of redundant links in T:

• Bypass rings of optional diameter

• Alternative paths in the event of failure

• Location & routing among the fragments

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### BR Platform

• Failure recovery

Bypass routing

Tree reconnection

Bypass rings

BC(FC)

n1

BRT(n1,4)

BRT(n2,2)

BRT(n1,3)

BRT(n1,2)

FC

n1

n2

TR= (TM\FC, CE’ )

n2

T = (TM, CE)

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### BR Platform

• Elemental steps of the recovery

• Initialization of the platform

• Failure detection

• Designated nodes discovery

• Tree reconnection

• Bypass rings reconfiguration

Bypass routing

Correctness

&

Completeness

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

### Bypass Routing

• Partially ordered tree (POT)

Ordered rays

Ordered neighbor

sequence

R-(A0,3C)

R+(A0,3C)

17

CE

E8

9F

BT(A0,3C)

B9

72

67

79

09

0F

3C

A0

93

B2

1D

SeqT(A0)

24

SeqT(3C)

42

T = (TM, CE)

5E

4A

F7

11

R+(A0,3C)

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Bypass Routing

• Bypass ring BRT(n, d)

R+(n,n1)

R-(n,n0)

dmax = 4

BT(n,n1)

BRT(n,4)

BRT(n,dmax)

BRT(n,3)

BT(n,n0)

n1

BRT(n,2)

n0

R-(n,n1)

R+(n,n2)

R+(n,n0)

n2

n

n3

R-(n,n3)

SeqT(n)

BT(n,n2)

R+(n,n3)

BT(n,n3)

R-(n,n2)

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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BRT(nm,dmax)

BRT(n2,5)

BRT(n2,4)

BRT(n1,3)

BRT(n1,2)

### Bypass Routing

• Bypass rings

R+(n,n1)

ndmax

n5

n4

n3

FC

n2

n1

n

BT(n,n1)

T = (TM, CE)

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Bypass Routing

• Routing algorithm

• <FC>T = BT(ni, nj), njAT(ni)  FC

ni1

nj1

BC(FC)

BT(ni2,nj2)

BT(ni3,nj3)

FC

T = (TM, CE)

nj3

R+(ni1,nj1)

ni3

nj2

ni2

BT(ni1,nj1)

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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BRT(A0,4)

BRT(3C,3)

BRT(3C,2)

### Bypass routing

• Example

BC(FC)

R+(72,3C)

CE

17

E8

9F

72

B9

0F

67

FC

79

09

3C

A0

93

B2

1D

24

T = (TM, CE)

42

5E

4A

F7

11

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Bypass Routing

• Properties

• Memory overhead at node nT:O(degT(n) * dmax)

• Routing is successful iflenX(ni, ni+1)  dmax, X = R+(ni, nj)for all neighborsni andni+1 BC(FC)

• Lower bound of maximum size ofFC:dmax/2 nodes for arbitrary clusters

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

• Guarantees correctness

• Communication structure – BC(FC)

• Node states

• Passive – initial state of the election

• Relay – election is lost

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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ID(nN-1) < ID(n0)

• LLE on ordered rings

ID(n0) < ID(n1) < ... < ID(nN-1)

ELECTION(n0)

n0

nN-1

ID(n0) < ID(n1)

n1

ELECTION(n1)

FC

n6

n2

ID(n1) < ID(n2)

n

BC(FC) = BRT(n,2)

SeqT(n)

n5

n3

n4

<FCAT(FC)>

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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A1.BA < A1.16

• LLE in partially ordered trees

Sweep process

Hierarchical identifier

HIDT(nr,ni)

ELECTION(4F.*)

BC(FC)

R+

HIDT(4F,D8)

D8

4F.A1.BA.D8

SWEEP(4F.A1)

BA

HIDT(4F,97)

97

4F.A1.BA.97

ELECTION(A1.BA.97)

A1

4F

HIDT(4F,16)

4F.A1.16

16

nr

SeqT(nr)

SeqT(A1)

FC

<FCAT(FC)>

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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17

9F

67

79

93

24

3C.A0 < 3C.A0

A0.B9 < A0.1D

42

5E

4A

F7

11

• Example

CE

ELECTION(3C.A0.1D)

E8

72

FC

B9

SWEEP(3C.A0)

0F

nr

nr

09

3C

A0

ELECTION(A0.B9.CE)

B2

1D

T = (TM, CE)

<FCAT(FC)>

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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• Properties

• Average message complexity:O(N logbN); b is the average branching factor of FC nodes in T

• Time complexity: O(N)

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

### Tree Reconnection

• Reconnection methods

• Reconnect the fragments located by the routing algorithm

• Abide by the results of LLE

• Designed to meet the specific application requirements

• Influence properties of the restored tree

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Tree Reconnection

• LR method

BC(FC)

n1

n2

n3

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Tree Reconnection

• HR-x method

HR-1

(q0, qi) if i  1 (mod x)

(qi-1, qi) otherwise

BC(FC)

n1

= q0

q3

q1

q2

q2

q1

n2

= q0

= q3

n3

q5 =

q0 =

q1

q4

q2

q3

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Tree Reconnection

• HR-x method

HR-2

(q0, qi) if i  1 (mod x)

(qi-1, qi) otherwise

BC(FC)

n1

n2

n3

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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17

9F

67

79

93

24

42

5E

4A

F7

11

### Tree Reconnection

• Example

CE

ELECTION(3C.A0.1D)

E8

72

FC

B9

SWEEP(3C.A0)

0F

09

3C

A0

ELECTION(A0.B9.CE)

B2

TR= (TM\FC, CE’ )

1D

<FCAT(FC)>

HR-2

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Tree Reconnection

• Properties

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Tree Reconnection

• Properties

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

### Summary of Results

• Properties of the BR platform

• O(degT(n) * dmax)

• Average message complexity:

• O(N logbN) for arbitrary failures

• Nfor single failures

• Lower bound of max. recoverable failure:

• dmax/2 nodes for arbitrary failed clusters

• dmax-1 nodes for internal failed clusters

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Summary of Results

• Simulation results

• Successfully recovered cluster

• Average diameter: dmax-2

• Average size: 1.5 dmax

• Linear recovery time

• dmax parameter

• Controls fault-tolerance vs. costs

• dmax=4 provides ample tolerance for GFS

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Summary of Results

• Properties of the platform

• Locality

• Multiple failure recovery

• Scalability

• Application requirements consideration

• Optional level of fault tolerance

• Protection selectivity

• Designated nodes discovery

• Tree reconnection method

• Independence of the protected tree type

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Summary of Results

• Applications

• Overlay multicast

• Applicable in all types

• Network-layer multicast

• Extension with BR(n,1) needed

• Sample application – GFS multicast

• Designed for large-scale P2P systems

• Based on a layered administrative hierarchy

• Employs BR platform to achieve fault-tolerance

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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### Agenda

• Introduction

• Solution

• BR Platform

• Bypass Routing

• Tree Reconnection

• Summary of Results

• Conclusion

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

### Conclusion

• Thesis summary

• Analysis of overlay trees environment and identification of recovery properties

• Proposal of BR platform

• Design of the specialized leader election

• Illustration of the tree reconnection

• Simulation of the platform

• Outline of the overlay multicast scheme

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### Conclusion

• Ideas for further research

• Autonomous management of fault-tolerance level and protection selectivity

• More sophisticated tree reconnection methods

• Extension of the platform fornetwork-layer multicast

Vladimír Dynda: Failure Recovery of Overlay Tree-based Structures

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• Thank You