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By: Swetha Kendyala ske009@latech

Software Rejuvenation. By: Swetha Kendyala ske009@latech.edu. Introduction.

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By: Swetha Kendyala ske009@latech

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  1. Software Rejuvenation By: Swetha Kendyala ske009@latech.edu

  2. Introduction • When software applications execute continuously for long periods of time, the processes corresponding to the software in execution age or slowly degrades with respect to the effective usage of their system resources. Process aging will affect the performance and eventually cause the application to fail.

  3. What is Software Rejuvenation? • The act of gracefully terminating an application and immediately restarting • Goal: Prevents unexpected error termination by terminating the program before it suffers an error

  4. Intended Use • Software rejuvenation is primarily indicated for servers where applications are intended to run indefinitely without failure

  5. Why do applications fail? • Process Aging: gradual degradation of application performance, over time, that may lead to premature program termination

  6. Causes • Memory leaks • Unreleased file locks • File descriptor leaking • Etc.

  7. Software Rejuvenation • Periodic preemptive rollback of continuously running applications to prevent failures in the future

  8. Transition Model For SW without Rejuvenation Transition Model For SW with Rejuvenation

  9. Downtime and cost without rejuvenation • Pf = • Downtimew/o r(L) = Pf * L • Costw/o r(L) = Pf * L * cf

  10. Pp = Pf = Pr = P0 = Downtimew r(L) = (Pf + Pr) * L Costw r(L) = (Pf * cf + Pr * cr) * L Downtime and cost with rejuvenation

  11. Thresholds - Goal Goal is to stay in S0 for the longest amount of time

  12. Thresholds cont. • To see how r4 affects downtime and cost, lets differentiate the previous equations with respect to r4

  13. Thresholds cont. • Downtime: • If r3 is dominant, the derivative becomes negative and downtime decreases when r4 increases thus rejuvenate at state Sp • If r3 is small, slow recovery from SR, downtime increases as r4 increases

  14. Thresholds cont. • Cost = • When cr is dominant, cost increases as r4 increases, implies no rejuvenation benefit • When cr is small, cost decreases as r4 increases

  15. Thresholds cont. • Overall, costs need to be calculated for individual programs • For best results: perform rejuvenation at state SP (r4 = ∞) or don’t perform rejuvenation (r4 = 0)

  16. Example 1 • MTBF = 12 months;  = 1/(12*30*24) • Takes 30 min to recover from unexpected error; r1 = 2 • Base Longevity is seven days; r2 =1/(7*24) • If rejuvenation is performed, mean repair time after rejuvenation is 20 minutes; r3 = 3 • Ave. Cost of unscheduled downtime due to failure, cf, is $1,000/hour • Ave. Cost of scheduled downtime during rejuvenation, cr, is $40/hour

  17. Example 2 • MTBF = 3 months;  = 1/(3*30*24) • Takes 30 min to recover from unexpected error; r1 = 2 • Base Longevity is three days; r2 =1/(3*24) • If rejuvenation is performed, mean repair time after rejuvenation is 10 minutes; r3 = 6 • Ave. Cost of unscheduled downtime due to failure, cf, is $5,000/hour • Ave. Cost of scheduled downtime during rejuvenation, cr, is $5/hour

  18. Example 3 • MTBF = 3 months;  = 1/(3*30*24) • Takes 2 min to recover from unexpected error; r1 = 0.5 • Base Longevity is 10 days; r2 =1/(10*24) • If rejuvenation is performed, mean repair time after rejuvenation is 10 minutes; r3 = 6 • Ave. Cost of unscheduled downtime due to failure, cf, is $5,000/hour • Ave. Cost of scheduled downtime during rejuvenation, cr, is $5/hour

  19. Implementation • Implementation of Software Rejuvenation is fairly easy. • Cron Jobs can be set to restart the application at various intervals • watchd can be used to detect if applications have failed and restart them

  20. Real World Examples • BILL-DATS II Collector • Billing collection system used by AT&T long-distance network • Set to rejuvenate after 1 week • Hasn’t prematurely failed after several year

  21. “S” Scientific Speech synthesis system • Long running scientific application • Used to process several hundred sentences over the course of many days • Found to fail after 100 sentences • Rejuvenates after 15

  22. Conclusions: • Decision to use Software Rejuvenation depends on predetermined failure rates and associated costs. • r4 = 0 , No rejuvenation • r4 = ∞ , Rejuvenation

  23. Questions???

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