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

SRDS’03 CUHK Outline Introduction A mobile environment – Wireless CORBA Performance analysis with and without checkpointing Analytical results and comparisons Conclusions

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

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

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

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

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

SRDS’03 CUHK Expected Program Execution Time Expected repair time Expected program execution time without checkpointing Laplace transform for cumulative distribution function

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

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

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

SRDS’03 CUHK Expected Program Execution Time Expected sojourn time in State 3 Expected program execution time with equi-number checkpointing = m

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

SRDS’03 CUHK Optimal Checkpointing Interval Minimize the expected program execution time or maximize the average effectiveness

SRDS’03 CUHK Beneficial Condition Checkpointing improves the performance

SRDS’03 CUHK Analytical Results and Comparisons (1) Equi-number checkpointing with respect to checkpoint number

SRDS’03 CUHK Analytical Results and Comparisons (2) Checkpointing vs. without checkpointing

SRDS’03 CUHK Average effectiveness vs. message arrival rate and handoff rate Analytical Results and Comparisons (3)

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