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

Jump to first page Overview n Key features n Request processing steps n Server architectures n Flash implementation n Performance n Simulations/Comparisons n Conclusions n Discussion

Jump to first page Key features n A new Web server architecture n Aggressive optimizations n Portable n High performance across a wide range of workloads

Blocking steps of a request n Disk blocking u Find File u Read File n Network blocking u Accept Connection u Read Request u Send Header u Send Data

Multi-process architecture n Pros: u no synchronization necessary n Cons: u difficult to perform optimizations

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

SPED architecture n Pros: u No synchronization u No context switching n Cons: u Disk reads block

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

Jump to first page Flash Cons: n Extra cost wrt SPED for IPC between the main process and the helpers n More memory requirements than SPED n OTHERS?

Flash optimizations and caches n Memory-mapped files n Byte alignment (writev)

Performance n Apache(MP) n Zeus(SPED) n Flash(AMPED) n Flash-MT n Flash-MP n Flash-SPED

Single file test

Trace test

Trace test w/ varying dataset size

Individual optimization effects

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

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