Fuego Event Service: Towards Modularity in Event Routing Sasu Tarkoma Rutgers-Helsinki Workshop 9.5.2006.

Fuego Event Service: Towards Fuego Event Service: Towards Modularity in Event RoutingModularity in Event Routing

Sasu Tarkoma

Rutgers-Helsinki Workshop

9.5.2006

ContentsContents

•Introduction

•Content-based routing

•Challenges

•Fuego event service

•Routing blocks: posets and forests

•DoubleForest

•Conclusions

IntroductionIntroduction

•Information dissemination solutions are needed by many distributed applications

– Content delivery• News, alerts, stock market information,

metadata, presence information,…– Monitor data (sensors)– Control data (actuators, robots,…)

•Motivates research and development of efficient distributed dissemination systems

– Event-based systems and Publish/Subscribe– Reusable building blocks for high-level routing

Event-based Systems and Event-based Systems and Publish/subscribePublish/subscribe

•Event delivery from publishers to subscribers– Event is a message with content– One-to-many, many-to-many– Builds on messaging systems and store-and-forward

•A frequently used communication paradigm– Decoupling in space and time– Solutions from local operation to wide-area

networking– Proposed for mobile/pervasive computing

•The event service is a logically centralized service – Basic primitives: subscribe, unsubscribe, publish

•Various routing topologies and semantics

SubscriptionsSubscriptions

•Subscriptions are described using filters– Filter: a stateless Boolean function

• Defines a subspace of the content space• A single event is a point in the content space

– Selects a subset of published events– Expressive interest definition and content-matching– Content model typically typed tuples or XML

Content-based RoutingContent-based Routing

•Filters select events based on the content of event messages

•Can be seen as content-based addressing

•More expressive than topic, subject, or header-based routing

•Research projects and prototype systems• Siena, Rebeca, Hermes,..

•Three central design considerations– Router topology– Interest propagation mechanism– Filtering language

Example of Siena-style Content-based Example of Siena-style Content-based RoutingRouting

B

C

Publisher

Subscriber

A

I want to publish

information

I want information that

matches my interests.

OverlayRouting

infrastructure

ChallengesChallenges

•How to manage large numbers of filters?– Covering relations (Siena)

• Prevent propagation of filters that are covered by existing filters

• The covering relation is a partial order• Filters poset (partially ordered set)• [0,10] covers [2,5]

– Filter merging (Rebeca)• Combine two or more input filters into a single

filter• Reduces processing overhead• [0,10] or [9,20] can be merged to [0,20]

Challenges continuedChallenges continued

•How to cope with mobile users?– Disconnected operation

• Buffering and queue management– Mobile subscribers / publishers

• Handover protocol for relocating subscriptions and updating the topology

• Multiple indirection points on the overlay network• Covering/merging complicate mobility support

– General requirements • fast convergence of the subscription topology• mobility-safety: no false negatives

Example HandoverExample Handover

B

C

Producer

Subscriber

A

1. Advertise

Subscriber 3. Roam

4. Update topology

5. Transfer buffered, possible teardown

Subpath that must be updated

2. Subscribe

Main Research ObjectivesMain Research Objectives

•Only a few data structures have been proposed for filter-based content-based routing. Is it possible to develop more efficient structures?

•How to take context information into account?

•How to modularize the routing process with reusable components?

•How to integrate filter merging with routing data structures?

•What handover protocols are efficient? What topologies are mobility friendly and efficient?

Research MethodologyResearch Methodology

•Content-based routing and data structures

– Formal definition

– Analysis of correctness

– Prototype implementation

– Empirical evaluation with benchmarks

•Mobility support

– Formal definition

– Analysis of correctness

– Evaluation using simulation

Fuego Event SystemFuego Event System•Scalable distributed event framework for mobile computing

•The Fuego event router consists of two parts:

– access server functionality with buffering and handover support for mobile clients, and

– extensible routing core for distributed operation

•New data structures for efficient content-based routing:

– poset (partially ordered set)-derived forest

– the forest is considerably more efficient than dag (directed acyclic graph) - based structures

•Rendezvous-based mobility support for fast handovers and subscription topology updates

– RP or paths to RP are updated instead of the whole topology

Routing BlocksRouting Blocks

Filters Poset

k neighbours + local clients

Forest (PF)

n local clients

Forest (NRF)

k neighboursn local clients

Forest (NRF)1 master k slave routers

n local clients

Filters Poset

k neighbours + local clients

Forest (PF)

n local clients

Efficient Matcher

n local clients

Notifications.

Add/del notify

Peer-to-peer Peer-to-peer HierarchicalExternal matchers

This is a set of generic building blocks for filter cover-based routing.

Can be extended with optimizations such as pruning and caching.

Merging BlocksMerging Blocks

Filters Poset

k neighbours + local clients

Poset-derived Forest

n local clients

Root Merger

Aggregate Merger

Non-redundant Forest

1 master routerk slave routers

Poset-derived Forest

n local clients

Root Merger

Root Merger

SlaveSlave

master

PosetBrowserPosetBrowser

Filters and ContextFilters and Context

•We propose to represent context using filters

– Support for points and subspaces (for example ranges)

– Use filters for both queries and profiles.

• A query defines a collection and is matched against profiles.

• A profile describes the context of an object

• Two semantics: cover and overlap

•A set of user interest context query filter subspace of context space

•A set of context metadata context profile filter subspace of context space

DoubleForestDoubleForest

•DoubleForest data structure

– Combines two poset-derived forests for generic context matching.

– One forest for queries, one for profiles.

•Support for both subspace matching and temporal profiles.

•Mappings are updated during add/del.

•Optimizations possible using forest structure.

•Significantly better performance to set-based iteration using filter covering.

•Experimental results indicate that overlap based matching has more overhead than cover.

DoubleForest Data StructureDoubleForest Data Structure

aa

ccbb

dd ee

Profiles P = { a,b,c,d,e }

Type=locationSubtype=officeX = 10Y = 20Diameter = 400

Type=locationSubtype=officeX = 10Y = 20Diameter = 400

11

3322

44

55

Type=locationSubtype=officeX [7,14]Y [18, 22]

Type=locationSubtype=officeX [7,14]Y [18, 22]

Queries Q = {1,2,3,4,5}

MAPPINGSMPQ: P (Q)MQP: Q (P)

Updated onadd and del operations

for the structures.

MAPPINGSMPQ: P (Q)MQP: Q (P)

Updated onadd and del operations

for the structures.

Query matches profile

DataSpace ArchitectureDataSpace Architecture

ProfileStore

Object and dir. sync.

When to sync?

Client Terminal

6. Context sync rules

3.Context Objecttracking rules

CollectionContents based on context

Augment objects withcontext

Synchronization Server

PoliciesACRs

5. Updates

7. Sync object / directory (peer-to-peer)

2. Make object available / unavailable

4. Sub/Unsub

Keep track of context subscriptions and notify

when an object is added/removed that

matches with the subscr.

Profile &QueryStore

Add new object with context profile to the

directory

1. Context

ConclusionsConclusions

•The poset-derived forest data structure for efficient filter cover-based routing

•Construction of routing systems using reusable building blocks, namely posets and forests

•A formal framework for filter merging and integration with the routing structures

•The DoubleForest data structure that extends the basic content-based routing model with temporal content and allows content defined using subspaces

•A formal treatment of client mobility in publish/subscribe and analysis of different mobility support protocols

•Live demos on the web: www.hiit.fi/fuego/fc/demos

•Thesis available on the web: ethesis.helsinki.fi