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SRDS’03 Performance and Effectiveness Analysis of Checkpointing in Mobile Environments Xinyu Chen and Michael R. Lyu The Chinese Univ. of Hong Kong Hong Kong Florence, Italy
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SRDS’03 CUHK Outline Introduction A mobile environment – Wireless CORBA Performance analysis with and without checkpointing Analytical results and comparisons Conclusions
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SRDS’03 CUHK Introduction Checkpointing and Rollback Recovery Checkpointing Save program ’ s states during failure-free execution Repair bring the failed device back to normal operation Rollback reload the program ’ s states saved at the most recent checkpoint Recovery Reprocess the program, starting from the most recent checkpoint by applying the logged messages, until the point just before the failure
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SRDS’03 CUHK Wireless CORBA Architecture Visited Domain Home Domain Terminal Domain Access Bridge Static Host Terminal Bridge GIOP Tunnel ab 1 ab 2 mh 1 GTP Messages Control message Computational message GIOP: General Inter-ORB Protocol GTP: GIOP Tunnel Protocol
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SRDS’03 CUHK Wireless CORBA Architecture Visited Domain ab 1 ab 2 Access Bridge Static Host Home Domain Home Location Agent Terminal Domain Terminal Bridge GIOP Tunnel mh 1 Terminal Domain Terminal Bridge GIOP Tunnel GIOP Tunnel mh 1 Terminal Domain Terminal Bridge GIOP Tunnel mh 1 Terminal Domain Terminal Bridge Access Bridge Handoff: a mechanism for a mobile host to seamlessly change a connection from one Access Bridge to another
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SRDS’03 CUHK Program’s Termination Condition GTP messages Control message Computational message: the number is not changed A program on a mobile host is successfully terminated if it continuously receives n computational messages Formulate the expected program execution time with message number n
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SRDS’03 CUHK State Transition without Checkpointing State 0 – normal, State 1– repair, State 2 – handoff 0 21 Generally distributed random variables H: handoff time R: repair time
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SRDS’03 CUHK Expected Program Execution Time Expected repair time Expected program execution time without checkpointing Laplace transform for cumulative distribution function
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SRDS’03 CUHK Equi-number Checkpointing Take checkpoints according to the number of received messages (a) Divide the program execution into m equal intervals (m=n/a) Equi-number checkpointing with respect to message number Message number in each checkpointing interval is not changed Equi-number checkpointing with respect to checkpoint number Checkpoint number is not changed
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SRDS’03 CUHK State Transition in Equi-number Checkpointing State 3 – Composite repair State 4 – Composite checkpointing 0 2 3 4 /a A generally distributed random variable C: Checkpointing time
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SRDS’03 CUHK Composite States State 3 – Composite repair State 5 – repair, State 6 – rollback, State 7 – handoff 567 3 State 4 – Composite checkpointing State 8 – checkpointing, State 9 – handoff 4 89 67 9
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SRDS’03 CUHK Expected Program Execution Time Expected sojourn time in State 3 Expected program execution time with equi-number checkpointing = m
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SRDS’03 CUHK Average Effectiveness Effective interval: a program produces useful work towards its completion Wasted interval: Repair and rollback Handoff Checkpoint creation Wasted computation Average Effectiveness: how much of the time an MH is in effective interval during an execution
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SRDS’03 CUHK Optimal Checkpointing Interval Minimize the expected program execution time or maximize the average effectiveness
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SRDS’03 CUHK Beneficial Condition Checkpointing improves the performance
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SRDS’03 CUHK Analytical Results and Comparisons (1) Equi-number checkpointing with respect to checkpoint number
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SRDS’03 CUHK Analytical Results and Comparisons (2) Checkpointing vs. without checkpointing
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SRDS’03 CUHK Average effectiveness vs. message arrival rate and handoff rate Analytical Results and Comparisons (3)
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SRDS’03 CUHK Conclusions Introduce equi-number checkpoiting strategies Derive expectations of program execution time with and without checkpointing Obtain average effectiveness Identify the optimal checkpointing interval Identify the beneficial condition Obtain analytical results and comparisons
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