1. Publisher Mobility in Distributed Publish/Subscribe Systems Vinod Muthusamy, Milenko Petrovic, Dapeng Gao, Hans-Arno Jacobsen University of Toronto June 10, 2005 4th International Workshop on Distributed Event-Based Systems (DEBS'05)

2. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 2 Motivation Explosion of information producers  Blogs, wikis, podcasting, photo sharing Mobility of users  Cell phones, PDAs, sensors Mobile information producers  Traditionally wired publishers can increasingly be mobile  New types of publishers SMS, camera phones, location based services Pub/sub data dissemination  Well suited to mobile clients Decoupling, filtering Mobility of information producer has not been studied in pub/sub  Breaks common pub/sub assumption

3. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 3 Publisher Mobility Scenarios Journalists with blogs  Update blogs on location  Upload pictures from camera phone Police patrol car  Send status updates Traffic, accidents, parts failures Mail delivery  Track delivery status, location updates Publisher 12

4. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 4 Agenda Background  Context  Subscriber mobility Publisher mobility  Problem  Solutions Evaluation  Setup  Results Conclusions

5. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 5 Context Part of Toronto Publish/Subscribe System (ToPSS)  Improve expressiveness Approximate matching, location queries, XML, RDF, composite subscriptions, historic subscriptions, etc.  Distributed issues Fault tolerance, load balance, reliability  New environments MANETs, P2P overlays, sensor networks Mobile-ToPSS project  Subscriber mobility [MDM’04] Based on JEDI, SIENA work  Publisher mobility [DEBS’05]  Effects of routing computations [Mobicom’05]  Content based routing in MANET [Mobiquitous’05]

6. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 6 Distributed Publish/Subscribe Advertisements flooded  Create adv tree Subscriptions along reverse adv path  Create multicast tree Publications along reverse sub path Publisher Subscriber...  Advertisements  Subscriptions  Publications

7. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 7 Subscriber Mobility Problem Matching publications during disconnection  Stored by broker  Replayed upon reconnection “State” transfer is expensive  Double message load with only 10% of mobile subscribers [MDM’04] No state lost when publishers are disconnected  No problem with mobile publishers? 12 Subscriber

8. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 8 Publisher Mobility Problem Adv and sub trees Moveout: both trees torn down Movein: both trees rebuilt Expensive  Network load: May be # ads > # subs  No delivery until tree constructed Distinguish temporary disconnections t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher 12...

9. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 9 Publisher Mobility Problem Adv and sub trees Moveout: both trees torn down Movein: both trees rebuilt Expensive  Network load: May be # ads > # subs  No delivery until tree constructed Distinguish temporary disconnections t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 movein Publisher 12...

10. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 10 Prefetching Optimization Exploits knowledge of future mobility patterns Concurrent  Construction at new broker  Teardown at old broker Tree construction time hidden from user t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher 12...

11. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 11 Prefetching Optimization Exploits knowledge of future mobility patterns Concurrent  Construction at new broker  Teardown at old broker Tree construction time hidden from user t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 movein Publisher 12...

12. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 12 Proxy Optimization Maintain trees from several brokers Advantageous if restricted mobility region t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher 12... movein Publisher

13. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 13 Delayed Optimization Maintain trees at old broker for some time Allow new tree to graft onto old tree Remove extraneous portions of old tree t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher 12... movein Publisher

14. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 14 Evaluation: Setup Simulation Environment  ns-2 network simulator  Implemented mobility optimizations Parameters  Topology Metropolitan Area Network 4 levels of degree 4  64 leaf brokers  Subscribers: 500  Publishers: 50  Locality: random, 30%, 60%, 90%  Mobility Static subscribers, mobile publishers Random speeds (5km/h, 50km/h, 100km/h) Metrics  Tree rebuild load  Tree rebuild time, delivery ratio 64 1

15. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 15 Publisher Scalability Standard and Prefetching >> Proxy and Delayed Prefetching worse due to extra control messages Delayed better due to smaller tree deltas

16. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 16 Publisher Scalability Probe tree completion Prefetching is fastest  Starts early Standard is slowest  Almost 4s Delayed close to Prefetching Note: time is not known to publisher

17. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 17 Publisher Scalability Tree rebuilding cost  Best: Delayed, Proxy  Worst: Standard, Prefetching Tree rebuilding time  Best: Prefetching, Delayed  Worst: Standard Prefetching  Good for the user  Bad for the network Delayed  Good for user and network  Practical

18. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 18 Publication Locality 250 publishers Vary publication similarity Standard and Prefetching approach Proxy and Delayed

19. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 19 Publication Locality Time from publish to notification Again, Standard and Prefetching approach Proxy and Delayed

20. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 20 Publication Locality With sufficient publication similarity, optimizations have diminishing benefit  Tree rebuilding cost  Delivery latency

21. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 21 Conclusions The publish/subscribe model is well suited to mobile applications  But publisher mobility has not been evaluated Publisher mobility is expensive  Breaks conventional assumptions  Tree rebuilding imposes large cost Must distinguish temporary vs. permanent disconnection  Delayed has best performance and is most practical Future Work  Other scenarios: realistic traces, mobile subscribers  Develop more optimizations

22. June 10, 2005 (DEBS ’05) Mobile-ToPSS (University of Toronto) 22 Publisher Mobility in Distributed Publish/Subscribe Systems Thank you