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Atomic Transaction Processing in Mobile Ad-Hoc Networks

Joos-Hendrik Böse http://www.cocoda.de Databases and Information Systems Group Freie Universität Berlin. Atomic Transaction Processing in Mobile Ad-Hoc Networks. TAs in Mobile Ad-Hoc Networks. P2P: Every node can act as TA coordinator or participant.

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Atomic Transaction Processing in Mobile Ad-Hoc Networks

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  1. Joos-Hendrik Böse http://www.cocoda.de Databases and Information Systems Group Freie Universität Berlin Atomic Transaction Processing in Mobile Ad-Hoc Networks

  2. TAs in Mobile Ad-Hoc Networks • P2P: Every node can act as TA coordinator or participant. • Movement, limited energy resources and user initiated shutdowns of mobile nodes cause lots of failures during TA processing. • Lots of recovery attempts !! Person-to-person scenario: Randomwaypoint mobility model

  3. Recovery Support for Atomic TAs in CoCoDa Impossible to prevent node or link failures • Participants and initiator are fixed, coordinator variable (sometimes) • CoCoDa middleware: Provides strategies for Transaction Recovery Participant failure • Recovery depends on the availability of log information. • Log information must be available at recovery time. Coordinator failure • Reliability of coordinator is crucial. • Failures must be recovered immediately. CoCoDa Solution • Save log information redundantly ->Shared Log Space CoCoDa Solution • Reliable backup coordinator. • Evaluatereliability of backup coordinators.

  4. Failure of Participants Shared Log Space (SLS) The SLS is a globally shared storage for preserving information in the MANET. Nodes cooperatively preserve transaction logs in the MANET for a certain mission time tm, with a certain availability. Participants register for a certain probability of log retrieval within tm before the transaction is started. In case the participant suffers from a failure C writes the TA log into the SLS. SLS controls dissemination to ensure prob. of successful log retrieval, within tm. • Mission time tm • Desired prob. of successful log retrieval • Failed participants reconnect to the MANET at unknown time in future. • Successful recovery of participants depends on the availability of log items. P3 P1 C P1 P4 P2

  5. Availability of Logs Problem to solve: On which/how many nodes must a log item be placed to achieve a certain availability for a certain mission time? • Dissemination strategy depends on MANET system model: • Context aware nodes vs. context unaware nodes • Dense vs. sparse MANETs Several models provided in CoCoDa - Simple models based on individual failure distributions of nodes. - Probability models based on birth-and-death processes

  6. Failure of Coordinator Careful choice of C and BC important! Based on energy and movement information. Must be reliable according to group of transaction participants. Different metrics, such as: Failure probabilities Simple additive weighting Fuzzy logic Energy resources BC Immediate recovery needed! P3 P1 P4 C • Backup-coordinator with veto-right • If C fails, participant can immediately switch to BC P2 Direction and speed

  7. Implementation / Emulation MANET Info TA Proc Replication SLS DataDis Communication Interface J2ME CDC OSGI JINI Ad-Hoc Wireless Connectivity (IEEE 802.11, Bluetooth) Developer IDE • Implemented in JAVA • Tests and evaluation using MarNET emulation • Xen Deployed to 20 Workstation (2GB RAM; 3,4GHz) • OSGi GPS sensor integrated • Successful emulation of scenarios with 200+ nodes. • Eclipse/Maven based control of emulation. • Automatic deployment of CoCoDa components. • Control of emulation process. • Analysis of debug output. CoCoDa Components

  8. Interests here • Mobile Data Management in general, especially TAs in mobile environments. • Reliability issues in mobile environments. • How to develop, test and evaluate large (mobile) distributed systems. Thank you for your attention 

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