Dept. of Computer Science & Engineering, CUHK Performance and Effectiveness Analysis of Checkpointing in Mobile Environments Chen Xinyu

u Introduction u Mobile Environment – Wireless CORBA u Performance and Effectiveness Analysis of Checkpointing u Conclusions and Future Work Outline

Introduction u Mobile Computing u Permanent failures Physical damage u Transient failures Mobile hosts Wireless links Environmental conditions

Checkpointing and Rollback Recovery u Checkpoint the saved program’s states during failure-free execution u Repair brings the failed device back to normal operation u Rollback reloads the program’s states saved at the most recent checkpoint u Recovery the reprocessing of the program, starting from the most recent checkpoint, applying the logged messages and until the point just before the failure

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

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

u Introduction u Mobile Environment – Wireless CORBA u Performance and Effectiveness Analysis of Checkpointing u Conclusions and Future Work Outline

Program’s Termination Condition u A program is successfully terminated if it receives N computational messages continuously

Assumptions u Failure occurrence, message arrival and handoff event  homogeneous Poisson process with parameter,  and  respectively u Failures do not occur when the program is in the repair or rollback process u A failure is detected as soon as it occurs

Execution without Checkpointing RY0Y0 X0X0 R F1F1 H1H1 Z0Z0 0 t FjFj HkHk m j (1)m j (N)m 1 (n 1 )m 0 (N) X(N) RepairHandoff HH

Conditional Execution Time without checkpointing

LST without checkpointing

LST and Expectation of Program Execution Time

Bounded Situations u Without handoff u Without handoff and failure

Execution with Equi-number Checkpointing CiCi R+C Y i (0) X i (0) R+C F i (1) H i (1) Z i (0) 0 t F i (j) H i (k) m ij (1)m ij (a)m i1 (n i1 )m i0 (a) X i (N,a) Repair + RollbackHandoff C i-1 Checkpointing HHCC

Conditional Execution Time & LST with Checkpointing

LST and Expectation of Program Execution Time

Average Effectiveness u Effective interval: a program produces useful work towards its completion u Wasted interval: Repair and rollback Handoff Checkpoint creation Wasted Computation u Average Effectiveness: how much of the time an MH is in effective interval during an execution

Optimal Checkpointing Interval

Beneficial Condition

Equi-number Checkpointing u Equi-number checkpointing with respect to message number Message number in each checkpointing interval is not changed u Equi-number checkpointing with respect to checkpoint number Checkpoint number is not changed

Equi-number Checkpointing with respect to Checkpoint Number

Equi-number Checkpointing with respect to Message Number

Comparison Between Checkpointing and Without Checkpointing

Average Effectiveness vs. Message Arrival Rate and Handoff Rate

Conclusions u Introduce an equi-number checkpoiting strategy u Derive LST and expectation of program execution time u Derive average effectiveness u Derive optimal checkpointing interval u Identify the beneficial condition

Future Work u Analytical model Message queuing effect during repair and recovery General event distributions u Fault tolerance in ad hoc network Without infrastructure support Self-organizing and adaptive

Thank You