Flash

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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
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Overview

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

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Key features

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

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Blocking steps of a request

• Disk blocking
• Find File
• Read File
• Network blocking
• Accept Connection
• Read Request
• Send Header
• Send Data

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Multi-process architecture

• Pros
• no synchronization necessary
• Cons
• difficult to perform optimizations

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Multi-threaded architecture

• Pros
• share global variables
• lower overhead for switching than MP
• Cons
• OS must provide support
• synchronization

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SPED architecture

• Pros
• No synchronization
• No context switching
• Cons
• Disk reads block

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AMPED architecture

• Pros
• Single process
• No context switching
• Helpers can be processes or threads
• No synchronization
• Non blocking
• Cons
• NONE?

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Flash Cons

• Extra cost wrt SPED for IPC between the main
  process and the helpers
• More memory requirements than SPED
• OTHERS?

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Flash optimizations and caches

• Memory-mapped files
• Byte alignment (writev)

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Performance

• Apache (MP)
• Zeus (SPED)
• Flash (AMPED)
• Flash-MT
• Flash-MP
• Flash-SPED

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Single file test
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Trace test
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Trace test w/ varying dataset size
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Individual optimization effects
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WAN emulation

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

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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?