1. Flash An efficient and portable Web server Vivek S. Pai Peter Druschel Willy Zwaenepoel Rice University presented by Andreas Anagnostatos CSE 291 Feb. 2, 2000

2. Overview • Key features • Request processing steps • Server architectures • Flash implementation • Performance • Simulations/Comparisons • Conclusions • Discussion

3. Key features • A new Web server architecture • Aggressive optimizations • Portable • High performance across a wide range of workloads

4. Blocking steps of a request • Disk blocking • Find File • Read File • Network blocking • Accept Connection • Read Request • Send Header • Send Data

5. Multi-process architecture • Pros: • no synchronization necessary • Cons: • difficult to perform optimizations

6. Multi-threaded architecture • Pros: • share global variables • lower overhead for switching than MP • Cons: • OS must provide support • synchronization

7. SPED architecture • Pros: • No synchronization • No context switching • Cons: • Disk reads block

8. AMPED architecture • Pros: • Single process • No context switching • Helpers can be processes or threads • No synchronization • Non blocking • Cons: • NONE?

9. Flash Cons: • Extra cost wrt SPED for IPC between the main process and the helpers • More memory requirements than SPED • OTHERS?

10. Flash optimizations and caches • Memory-mapped files • Byte alignment (writev)

11. Performance • Apache (MP) • Zeus (SPED) • Flash (AMPED) • Flash-MT • Flash-MP • Flash-SPED

12. Single file test

13. Trace test

14. Trace test w/ varying dataset size

15. Individual optimization effects

16. WAN emulation • Initial rise due to aggregation effects • MT declines due to per-thread switching and memory overhead • MP per-request overhead

17. Summary • AMPED combines cache behavior of SPED and disk behavior of MT and PS • Shared address space • No synchronization • Low overhead for helpers • High performance in real workloads • Portable (?) • Discussion... • Would you prefer Flash over a commercial server? • Other features missing?