Adaptive Content-based Routing In General Overlay Topologies

MIDDLEWARE SYSTEMSRESEARCH GROUP

Adaptive Content-based Routing In General Overlay Topologies

Guoli Li, Vinod Muthusamy

Hans-Arno Jacobsen

Middleware Systems Research Group

University of Toronto

http://padres.msrg.toronto.edu

Middleware 2008 @ Leuven, Belgium


Distributed Publish/Subscribe

An acyclic overlay is sensitive to: Congestion Broker failures

Benefits of a general overlay: Routing around congestion and failures Handling imbalanced workloads

Publisher

Subscriber

Subscription

Publication

Advertisement

Subscriber

Applications Business process execution e.g., BPEL Business activity monitoring Service discovery and integration …



Challenges With General Overlays

Subscriptions are routed in loops

Brokers receive duplicate subscriptions

Subscription copies exacerbate the problem

Same problem for publications

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3 4

5

1

6

Adv 1

Adv 2

S X

S

S



Agenda

Content-based routing protocol for general overlays Atomic and composite subscriptions Optimal publication routing

Evaluation Dynamic publication routing Adaptive composite subscription routing



TID-based Approach

Each advertisement is assigned to a unique tree identifier (TID)

Each subscription has a TID predicate with a variable

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Adv 1

Adv 2

XS



Subscription Routing

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3 4

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Adv 1

Adv 2

XS: [class=stock][symbol=*] [TID=$Z]

At Broker 1:

Adv1:

[class=stock][symbol=IBM] [TID=Adv1]

Adv2:

[class=stock][symbol=HP] [TID=Adv2]

S matching Adv1:

[class=stock][symbol=*][TID=Adv1]

S matching Adv2:

[class=stock][symbol=*] [TID=Adv2]

SA2SA1

S



Publication Routing

Each publication is assigned the TID of its matching advertisement e.g., p [class, stock][symbol,HP][TID,

adv_msg_id] Publications are routed:

Fixed TID routing: a publication is routed to subscribers along its advertisement tree.

Dynamic publication routing: a publication may be routed to subscribers across advertisement trees.



Fixed TID Routing

Property No broker receives

duplicate publication messages

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Adv 1

Adv 2

Sub

X

P

P



Dynamic Publication Routing

Publication’s TID is changeable

Routing heuristic Util = Routput / Rsending

Property Changing a publication’s

TID while in transit will not change the set of notified subscribers.

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Adv 1

Adv 2

Sub

X

P



Advantages

Retains the publish/subscribe client interface Speeds up subscription and publication

matching Avoids duplicate subscriptions and

publications Routes publications dynamically across

multiple alternatives Enables routing around failures, congestion

and load imbalances



Composite Subscription

AND

S1 S2

A composite subscription consists of atomic subscriptions linked by logical operators (e.g., AND, OR).

Composite subscription routing Topology-based routing Adaptive routing

e.g., CS= {[class=stock][symbol=YHOO][price>12]} AND

{[class=stock][symbol=MSFT][price<20]}



Topology-based CS Routing

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6Adv 1

Adv 2

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8

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CS={{S1 AND S2} ANDS3}CS

S2A2

S3A3

S1A1

CS’

Adv 3

CS’ ={S1 AND S2}

Broker 4 and 8 are the joint

point brokers



Adaptive CS Routing CS’s joint points are determined according to

potential publication traffic, bandwidth, latency, etc.

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1 3Adv 1

Adv 2

CS={S1 AND S2}

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1 3Adv 1

Adv 2

CS={S1 AND S2}



Cost Model Routing cost of CS

RC(CS)) = +

+

Subscription cardinality |P(S)| : The number of matching publicat

ions per unit of time.

|P(S)| =

|P(CS)| = |P(Sl)| + |P(Sr)| if op = or

subscription dest

Matching Engine

Routing Table

+

symbol=IBM B1

symbol=HP B2

input queue

output queue B1

output queue B2

Broker



Adaptive CS Routing

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3 4

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1

6Adv 1

Adv 2

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8

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CS={{S1 AND S2} ANDS3}CS

S2A2

S3A3

S1A1

CS’

Adv 3

CS’ ={S1 AND S2}

CS’



Evaluation

Setup Overlays of 32 brokers with different connection d

egrees Cluster (each node:1.86GHz, 4G) and PlanetLab Workloads:

Yahoo!Finance stock quote traces http://research.msrg.utoronto.ca/Padres/DataSets

Metrics End to end notification delay Network traffic



Dense vs. Sparser Topologies

20%

4%

Note: The benefit is not proportional to the connection degree.



Higher Publication Rate

stabilized



Publication Burst

Burst



With Broker Failures

1st failure

2nd failure



CS Routing Traffic



Conclusions Enables routing around failures, congestion and

load imbalances Allows publications routing across alternative

paths Improves the notification delay by 20%

Enables flexible CS routing Reduces 80% publication traffic Improves the notification delay by 55%

Simplifies solutions for failure recovery and load balancing



Questions?

A D R E SP

http://padres.msrg.utoronto.ca



More Publishers



Effect of Subscriber Distance

Distance Fixed(ms) Dynamic(ms) Improvement

6 Hops 47.202 47.568 -0.78%

10 Hops 64.477 52.895 17.96%

12 Hops 74.416 60.598 18.57%

Max Diff 57.65% 27.39%



On PlanetLab



CS Delay



Faster Matching with TIDs

Subscriptions are augmented with TIDs only once at the first broker.

Other brokers can route the subscription based on the TID alone.

Similar argument applies to publication routing.



Advertisement Routing

Each advertisement forms a spanning advertisement tree

Duplicated advertisements are discarded by brokers

Each advertisement is assigned a unique tree identifier (TID) e.g., a [class,eq,stock]……[TID,eq,adv_msg_id]

Subscription Routing Table (SRT) A set of [advertisement, last hop]



Subscription Routing

Each subscription has a TID predicate with a variable. e.g., s [class,eq,stock]……[TID,eq,$X]

The variable is bound to the TID of a matching advertisement

Publication Routing Table (PRT) A set of [subscription, {TID, last hop of

subscription }]

Adaptive Content-based Routing In General Overlay Topologies

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