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Towards Configurable and Adaptable Distributed Event Dispatching

IBM Boeblingen Lab. Politecnico di Milano. Michela Becchi becchi@de.ibm.com. Towards Configurable and Adaptable Distributed Event Dispatching. Outline. Introduction 4 Event Dispatching Algorithms Evaluation and Comparison Heterogeneous System Simulations Conclusions. Outline.

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Towards Configurable and Adaptable Distributed Event Dispatching

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  1. IBM Boeblingen Lab Politecnico di Milano Michela Becchi becchi@de.ibm.com Towards Configurable andAdaptable DistributedEvent Dispatching

  2. Outline • Introduction • 4 Event Dispatching Algorithms • Evaluation and Comparison • Heterogeneous System • Simulations • Conclusions Michela Becchi - 2

  3. Outline • Introduction • 4 Event Dispatching Algorithms • Evaluation and Comparison • Heterogeneous System • Simulations • Conclusions Michela Becchi - 3

  4. A6 A7 A5 A8 EVENT DISPATCHER A4 A9 A3 An A2 A1 The Context: “publish-subscribe” middleware • Reasons for Interest: • High number of applications with reactive behavior (e.g.: workflow systems, monitoring systems) or based on “publish/subscribe” communication paradigm (e.g.: newsgroup, subscriptions to web pages) • Need for integration of different and autonomous applications • Characteristics: • Anonymous, asynchronous and multicasting communication service • Decoupling among agents • Semantic suitable for describing applications exhibiting “reactive” behavior Michela Becchi - 4

  5. A6 Ed1 A7 A5 An A8 Event dispatcher Ed2 Ed3 A4 A9 A7 A8 A9 Ed4 Ed5 Ed6 A3 A6 An A2 A1 A1 A2 A3 A4 A5 From centralized to distributed solutions • topology: • Interconnection’s topology (hierarchical, connected graph, etc.) • Number and location of components • algorithms • system’s properties: • delivery of messages • ordering of reception • propagation’s transitories Michela Becchi - 5

  6. Outline • Introduction • 4 Event Dispatching Algorithms • Evaluation and Comparison • Heterogeneous System • Simulations • Conclusions Michela Becchi - 6

  7. “Local Subscribe” policy S S S N S “Global Subscribe” policy S S N Propagation algorithms (1) Michela Becchi - 7

  8. “Hierarchical” policy S “Advertise” policy S S N S S S S N S S N Propagation algorithms (2) Michela Becchi - 8

  9. Outline • Introduction • 4 Event Dispatching Algorithms • Evaluation and Comparison • Heterogeneous System • Simulations • Conclusions Michela Becchi - 9

  10. Comparison criteria • Traffic for messages’ propagation • Subscriptions and advertisements are less (frequent) than event notifications • Possible optimization in propagation of subscriptions and advertisements • Load at the different levels of the hierarchy • “Duration” of transitions and cost of confirmation algorithms • Dynamicity of dispatchers’ tree • Local processing • Recipients’ calculation (query) • Number of transmissions (writing on sockets) Michela Becchi - 10

  11. Summary of analysis • PROPAGATION’S TRAFFIC • Global Subscribe if • optimization in subscriptions’ propagation not necessary • medium-high locality between events’ “sources” and events’ “recipients” • Advertise if • many subscriptions and dispatchers (big tree) • high locality between events’ “sources” and events’ “recipients” • Hierarchical if • many subscriptions and dispatchers (big tree) • low locality between events’ “sources” and events’ “recipients” • Local Subscribe if • events’ broadcast • TRANSITIONS, CONFIRMATION MECHANISMS, LOCAL PROCESSING • Local Subscribe < Hierarchical < Global Subscribe / Advertise Michela Becchi - 11

  12. Outline • Introduction • 4 Event Dispatching Algorithms • Evaluation and Comparison • Heterogeneous System • Simulations • Conclusions Michela Becchi - 12

  13. A A A GS GS GS GS GS GS GS GS GS GS A A A A A A A H H H H H H H H H H GS A H A Heterogeneous System “Static” • Validity of propagation properties • Transparency to agents Perspectives “Dynamic” • Summary of topological constraints • Mono-directional policy switch: • from root, in increasing depth direction • (H -> GS, H -> A, A -> GS) • from leaves, in decreasing depth direction • (GS -> H, A -> H, GS -> A) • Heterogeneous configurations “useless” and acceptable only during transitions Michela Becchi - 13

  14. Outline • Introduction • 4 Event Dispatching Algorithms • Evaluation and Comparison • Heterogeneous System • Simulations • Conclusions Michela Becchi - 14

  15. DA 1 DB 1000 Simulations • GOALS: • Quantitative evaluation of performed analysis • Evaluation of the impact of network scenario on the performances of an event dispatching system • Evaluation of the reasons for • centralized vs. distributed • modification in dispatchers’ net topology • CONSIDERED METRICS: • “average latency” of event notifications • delay introduced by dispatchers • total delay (network + dispatchers) Michela Becchi - 15

  16. Delay introduced by dispatcher Recipients’ calculation (Socket) Transmissions Causes In the adopted model the delay is determined by distributions that do not consider the number of recipients (average  7,1 ms.) • Working areas: • 1) “under-saturation”: • queue  0 • dispatching time  7,1 m. • 2) “over-saturation”: • diverging queue • diverging dispatching time • 3) “saturation limit”: • queue with finite length (L) • dispatching time  L * 7,1 ms. Michela Becchi - 16

  17. “broadcast on bus” transmission technology delay due basically to collisions Ethernet Working on LAN (1) 1) f << fsat - centralized more performing than distributed 2) f > fsat - admissible policies: Advertise and Global Subscribe 3) ffsat - distributed more performing than centralized even with Hierarchical policy; little dispatcher tree preferable. Michela Becchi - 17

  18. Working on LAN (2) Over-saturation working area 3-level binary tree 4-level ternary tree Low subscriptions’ rate Not negligible subscriptions’ rate Michela Becchi - 18

  19. Working on WAN (1) internet: “cloud” causing delays following distributions with high variance exploitation of automatic generators of network topologies  concept of “network distance” Approaches dispatchers and agents directly connected to “ip-cloud” IP_CLOUD APPROACH LANs connected to “ip-cloud” 7 LANs connected into 2- and 3- level tree. Each LAN is connected to ip-cloud Michela Becchi - 19

  20. Working on WAN (2) SECOND APPROACH – examples in the under-saturation working area Variable locality index, not negligible subscriptions’ rate High locality index, variable subscriptions’ rate “Mixed” Scenario Michela Becchi - 20

  21. Outline • Introduction • 4 Event Dispatching Algorithms • Evaluation and Comparison • Heterogeneous System • Simulations • Conclusions Michela Becchi - 21

  22. Conclusions and future developments Summarizing... • Configurable and dynamic event dispatching system • Adopted policy • Number and location of components • Algorithms’ characterization and comparison • No optimal configuration • Application context characteristics (subscriptions’ and events’ rate, etc.) • Network scenario (LAN, WAN) • Introduction of heterogeneous systems and possibility of dynamic policy switching • Simulation • Validation of the analysis • Definition of dimensioning criteria depending on network scenario Possible developments… • Simulation: removal of simplifications, more sophisticated scenarios (dynamic) • Extension of the analysis and the proposal to more complicated topologies (e.g.: “unrooted” trees -> topological reconfiguration) Michela Becchi - 22

  23. Thank you ! Michela Becchi - 23

  24. Backup Michela Becchi - 24

  25. GS GS GS GS GS GS H H GS GS GS GS GS GS GS GS A H GS H H H H H H H H H H H GS H H Reasoning about configurations... • communication from subsystem GS to subsystem H working • communication from subsystem H to subsystem GS broken • intra-subsystem communication working • inter-subsystem communication working only in one direction! Configuration making sense only during policy transition! • subscriptions: H receive subscriptions from father and ignore them • event notifications: H may propagate useless event notifications to father Michela Becchi - 25

  26. Dimensioning criteria • LANand WAN ip-cloud scenarios (components directly connected to cloud) • each dispatcher in under-saturation area • number of dispatchers as low as possible • WAN scenario characterized by interconnected LANs • above rules within each LAN • depth of the overall tree (after interconnection of LANs) as low as possible • WAN topologies with low latency links and predefined collocation of agents • each dispatcher in the under saturation area • distribution of dispatchers in order to • reduce number of low latency links the messages should go through • maximize locality between event “producers” (notifiers) and “consumers” (subscribers) Michela Becchi - 26

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