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CS6320 – Web Services and Performance

CS6320 – Web Services and Performance. L. Grewe. Web Services. Services available via the Internet that complete tasks or conduct transactions. Self-contained, modular applications that can be described, published, and invoked over the Internet.

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CS6320 – Web Services and Performance

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  1. CS6320 – Web Services and Performance L. Grewe

  2. Web Services • Services available via the Internet that complete tasks or conduct transactions. • Self-contained, modular applications that can be described, published, and invoked over the Internet. • Can be automatically invoked by application programs.

  3. Web Services • May be invoked at one site or may combine results of several services executed at different sites.

  4. Performance concerns differ from standard Client/Server • May involve both web service processing and network delays • May be accessed by wide variety of devices -- desktop computers, PDAs, mobile phones, other servers • Access via wireless communication networks: dynamic connectivity, low bandwidth, high latency

  5. Performance concerns differ from standard client/server • Undpredictable nature of requests • Highly bursty • Varies with geographical location of clients, day of week, time of day • Highly variable size of requested objects • “Robot” access • Autonomous software agents that can consume significant amounts of system resources

  6. Types of servers providing Web Services • Web servers • Transaction servers • Proxy servers • Cache servers • Wireless gateway servers • Mirror servers

  7. Common problems • Insufficient bandwidth at peak times • Overloaded servers • Uneven server loads • Delivery of dynamic content • Shortage of connections between application servers and database servers • Failure of third-party servers • Delivery of multi-media content

  8. Example:Bill Paying Service • Portal offers bill paying service • Customers can pay variety of bills through the service • Uses services provided by others: • Debit authorization (100 tps capability) • Electronic funds transfer • Customer authentication

  9. Example:Bill Paying Service

  10. Example: Bill Paying Service • Portal B is bill paying service • Treat overall web service as ‘system’ • Treat component services as ‘devices’ • What is the capacity of B, given that the debit authorization service can support 100 tps and that each payment transaction requires 2 visits to the authorization service …..answer 50tps. (this assumes that the authentication is the slowest device).

  11. Review – web service can return many kinds of Web (HTTP) content

  12. Perception of Performance • User view: • Fast response time; no connections refused • Management view: • High throughput; high availability • Need to have quantitative measurements that describe behavior of Web service

  13. Metrics • Two most important; • Response time -- seconds • Throughput -- http_ops/sec, also bits/sec

  14. Other metrics • Hit • any connection to a web site, including in-line requests and errors • difficult to compare across sites • Visit • Series of page requests by a user at a single site • Inter-request times < timeout_value • Session • Series of consecutive and related requests made during a single visit • Inter-request times < timeout_value

  15. Other metrics • User-perceived response time • Set of geographically distributed agents poll the WS • Error rate • Increase indicates degrading performance • Examples: • Overflow of pending connection queue • For streaming services: • Jitter • Startup latency

  16. Most common measurements of Web service performance • End-to-end response time • Site response time • Throughput (req/sec or transactions/sec) • Throughput (Mbps) • Errors/sec • Visitors/day • Unique visitors/day

  17. Example - Travel Agency • Monitor for 30 minutes: • 9000 HTTP requests • Three types of objects delivered: • Html pages (30%, avg. size 11,200 bytes) • Images (65%, avg. size 17,200 bytes) • Video clips (5%, avg. size 439,000 bytes) • What is the throughput: • 9000 requests/1800 sec = 5 req/sec • What is the throughput in Kbps?

  18. Throughput in Kbps? • Xr = (total_req * class% * avg. size)/time • Xhtml = (9000 * 0.30 * 11,200*8)/1800 = 131.25 • Ximage = (9000 * 0.65 * 17,200*8)/1800 = 436.72 • Xvideo = (9000 * 0.05 * 439,000*8)/1800 = 857.42 • X0 = 131.25 + 436.72 + 857.42 • X0 = 1425.39 Kbps To support the Web traffic, the network connection should be at least a T1 line (1.544 Mbit/s ).

  19. QoS indicators for Web Services • Response time • Availability • Percentage of time a service is ‘live’ (serving customer requests) • Reliability • Probability that WS will perform in satisfactory manner for a given period of time under specified operating and load conditions • Predictability • Cost

  20. Input data needed to monitor QoS • Traffic • Performance • Usage patterns • Knowledge of average and peak load

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