“SUB-2-SUB” Self-Organizing Collaborative Content-based Pub/Sub Spyros Voulgaris, Etienne Rivière, Anne-Marie Kermarrec, Maarten van Steen

2/18 Publish/Subscribe What are pub/sub systems?  Subscribers register their interest  Publishers issue events  An event is delivered to all interested subscribers, and no others Here: Content-based Pub/Sub  Range subscriptions on multiple numeric attributes.

3/18 Current systems:  Centralized servers (e.g., Tibco)  Broker-based (e.g., Siena) Servers become a bottleneck/single point of failure  network size increases  node churn increases  more events are published Triggered interest in decentralized P2P solutions Current solutions

4/18 What kind of P2P system is suitable? Most research has focused on Structured P2P (DHTs)  Map attribute to peer Peers handling popular attributes get overloaded  Map (attribute,value) to peer Can lead to explosion of registrations for range subscriptions Meghdoot, based on CAN DHT, supports ranges too We show how Unstructured P2P can give a simple and efficient solution, supporting ranges Interest in P2P solutions

5/18 Sub-2-Sub: System Model Assume N attributes (real numbers)  A 1, A 2, …, A N Subscriptions are range (trivially exact) predicates on one or more attributes  E.g. A 2 ==3.07 && (2.5< A 4 <4.7)  One subscription per peer Events define exact values for all attributes  E.g. {A 1,A 2,A 3,A 4 } = {3, 0, 7, 10.5} The set of all possible events define the event space  It’s an N-dimensional, continuous space

6/18 Sub-2-Sub: Key Concept “Partition event space in homogeneous subspaces” (homogeneous subspace: all its events have the same subscribers)

7/18 Sub-2-Sub: Operation 1. Let subscribers of “near” subspaces discover each other 2. Organize subscribers of the each subspace in a ring 3. To publish an event, navigate to the target subspace, and hand the event to any one subscriber  Event reaches all and only interested subscribers, autonomously!

8/18 How do we build Sub-2-Sub? How do we…  Q1: …maintain connectivity in the face of churn / failures?  Q2: …form links between related subscribers?  Q3: …organize subscribers within a subspace in a ring? Each node  3 sets of links to other nodes  Managed by 3 gossiping protocols

9/18 We use the CYCLON gossiping protocol [S. Voulgaris, D. Gavidia, M. van Steen. Journal of Network and Systems Management, Vol. 13, No. 2, June 2005] Nodes maintain a few links to other nodes Periodically a node gossips to exchange some links CYCLON overlays have shown to:  Resemble random graphs  Be extremely robust to failures / churn  Fast adaptive to network changes Q1: Maintaining connectivity

10/18 We need some notion of distance In this case we use the Euclidean distance between two subscriptions  Note: Distance 0 denotes overlap Nodes gossip similarly to CYCLON,  but keep neighbors of minimum distance  “VICINITY” protocol [S. Voulgaris, M. van Steen. EuroPar 2005] Why not run VICINITY alone (without CYCLON)?  The network would fall apart in no time! Q2: Forming links (related subscr.)

11/18 We run VICINITY again, with another distance metric. Please refer to the paper! Q3: Organizing subscribers in rings

12/18 Sub-2-Sub: To recap Random subscribers (CYCLON) Overlapping subscr. (VICINITY) Ring links (VICINITY)

13/18 Performance Evaluation Simulated experiment:  10K nodes  3 attributes  For each attribute: Power-law (1/x^3) value popularity Uniformly random range widths Evaluation criteria  How fast the network self-organizes  How fast publishers reach target subspace  How fast events are disseminated

14/18 Self-organization evolution Each bar corresponds to 10,000 random events

15/18 Hops to reach target subspace # publishers

16/18 Hops for Event Dissemination # subscribers in subspace hops to complete dissemination

17/18 Summary Showed that Unstructured P2P can build overlays for apps as complex as pub/sub Sub-2-Sub  Accurate  All and only interested nodes receive event  Autonomous, Self-contained  No need for extra devices  Collaborative  Self-organized  Very scalable

18/18 Questions?

19/18 Ring sizes