1. Research Heaven, West Virginia PI: Katerina Goseva – Popstojanova Students: Ajay Deep Singh & Sunil Mazimdar Lane Dept. Computer Science and Electrical Engineering West Virginia University, Morgantown, WV katerina@csee.wvu.edu Performability of Web-based Applications

2. Research Heaven, West Virginia 2 Problem World Wide Web is the biggest existing distributed system so far –Huge number of Web clients - tens of millions and rising –Users demand 24/7 availability and response time within several seconds –However, very often they experience long and unpredictable delays (WWW - World Wide Wait) Problem: Traditional analysis and prediction methods do not work for Web

3. Research Heaven, West Virginia 3 Relevance to NASA Increasing use of Web-based technology at NASA Web sites Agency wide Control of daily mission operations from multiple geographically distributed locations via Internet (e.g., Web Interface for Telescience at JPL) Real-time applications remotely controlled/monitored over the Internet or an Intranet (e.g., Tempest embedded Web server at Glenn Research Center)

4. Research Heaven, West Virginia 4 Relevance to NASA Our empirical analysis is based on data extracted from actual Web logs of ten servers –Three public and three private Web servers at the NASA IV&V Facility –Lane Department of Computer Science and Electrical Engineering (CSEE) Web server –NASA Kennedy Space Center (NASA-KSC) Web server –Campus wide Web server at the University of Saskatchewan –Web server of the commercial Internet provider ClarkNet

5. Research Heaven, West Virginia 5 Approach Develop methods and tools that are general and powerful enough to provide flexible analysis and quality assurance of Web reliability, availability, and performance Develop scalable framework that combines measurements and models at different levels of detail and abstraction Reliability/Availability: based on typical usage patterns Performance: non-Poisson queuing theory Combine reliability / availability and performance and analyze their tradeoffs

6. Research Heaven, West Virginia 6 Approach Web access log analysis User session characterization Realistic workload Software/hardware resource utilization Application & hardware resource monitoring Web error log analysis Request-based and session-based error characterization Software/hardware failure/recovery characterization Performability model Session layer (user view) Service layer (software architectural view) System layer (deployment view) Reliability/ availability model Performance model Resource layer (hardware device view)

7. Research Heaven, West Virginia 7 Accomplishments Workload analysis Intra-session characteristics Intra-session characteristics Inter-session characteristics Inter-session characteristics Web log files Create relational database Errors and reliability analysis Errors and reliability analysis Unique errors (frequency & severity) Unique errors (frequency & severity) Request-based reliability Request-based reliability Session-based reliability Session-based reliability Unique files with errors Unique files with errors

8. Research Heaven, West Virginia 8 Accomplishments Empirical analysis of the Web workload, errors, request- based and session-based reliability for ten Web servers Error rates have heavy tail distributions 10-35% of the total number of errors are due only to 3 files Some examples Fixing the errors with the highest frequency of occurrence is the most cost effective way to improve Web quality

9. Research Heaven, West Virginia 9 Accomplishments We argue that session-based reliability is a better indicator of the users perception of the Web quality than request-based reliability

10. Research Heaven, West Virginia 10 Importance/benefits Innovative theoretical and empirical research results –Introduced and empirically analyzed new measures for session-based workload and reliability –Conducted detailed empirical study on Web errors, including severity level of errors, unique errors, and unique files with errors – measures that have not been considered earlier Practical value –The results of our research were actually used by Web administrators of the NASA IV&V and CSEE Web servers to improve their quality in a cost-effective way

11. Research Heaven, West Virginia 11 Next steps Performance attributes –Develop non-Poisson queuing theory Standard performance models (Queuing Networks & Layered Queuing Networks) assume Poisson arrivals Web workload is bursty (highly non-Poisson) Dependability attributes (reliability, availability) –Develop architecture-based models based on typical usage patterns Combine performance and reliability / availability models –Analyze tradeoffs among multiple quality attributes