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CS 623 Lecture #9

CS 623 Lecture #9. Yen-Yu Chen Utku Irmak. Papers to be read. Better operating system features for faster network servers. High-performance web site design techniques. Flash: An efficient and portable Web server. How the web works: HTTP and CGI explained. Web Performance. Issues:

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CS 623 Lecture #9

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  1. CS 623 Lecture #9 Yen-Yu Chen Utku Irmak

  2. Papers to be read • Better operating system features for faster network servers. • High-performance web site design techniques. • Flash: An efficient and portable Web server. • How the web works: HTTP and CGI explained.

  3. Web Performance • Issues: • Why is the web slow ? • Where does the time go ? • How to improve performance ? • Many techniques: • Caching, Prefetching • Web site/server performance • Wide area replication • Protocols

  4. Better OS features for faster network servers(Banga, Druschel, Mogul) • Performance of servers often disappointing given fast hardware • One reason: OS not designed for servers • Lot of time in kernel mode • High concurrency • Scalability • Need better OS support

  5. Server Execution Models • Process per request • Pre-forked processes • Event-based • One process • Use of select() • Thread-based • User level vs. Kernel level • Note: Dynamic content requires other processes that generate content

  6. Event Driven • Control thread should never block • Can use either SIGNALS or SELECT/POLL operations • SIGNALS do not scale well • SELECT also has problems with interface and implementation

  7. Event Driven • Non-blocking I/O problem not completely solved by AIO library • Need to rewrite code • Directory lookups, stat() • No select to detect completion

  8. Multi-Threaded • Kernel-level: High overhead • User-level: If one thread blocks, all threads in process block • “Scheduler Activations” help • Current thread implementations do not scale • Some techniques exist but are not part of current OS

  9. Scheduling/Resource Management • Kernel-level (network) processing not properly accounted for • May be charged to process running • Network has priority • Does not work within process • Problem for QoS

  10. New Features Proposed • Resource containers • Groups resources used by one connection • Has priority • Thread-based: container per thread (= connection) • Event-based: container per connection

  11. Efficient support for events • Application can tell kernel which descriptors they are interested in • Persists over multiple calls • Event notification • Preserves priorities • Queuing of events

  12. High-Performance Web Site Design Techniques(Iyengar, Challenger, Dias, Dantzig) • RR-DNS • TCP Routing • Web server accelerator

  13. RR-DNS • Routing to multiple web servers • Problems • Server side caching • Client side caching • Node failures

  14. TCP Routing • Many commercial products • Based on network processors • Using different load-based algorithms or simple round-robin scheme • Can be combined with RR-DNS

  15. Web Server Accelerators • Caches pages • Based on embedded OS • Could be based on network processor • Caching dynamic pages • DUP algorithm (Data Update Propagation) • ODG (Object dependence graph)

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