Flash: An efficient and portable Web server

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Flash An efficient and portable Web server

• Authors Vivek S. Pai, Peter Druschel, Willy
  Zwaenepoel
• Presented at the Usenix Technical Conference,
  June 1999

Presented by Richard Ta-Min
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Introduction

• Web servers need to be fast and able to service
  many requests concurrently
• Three web server architectures
• Multi-process and multi-thread
• Apache web server
• Single process event driven
• Zeus web server
• Asymmetric multi process event driven
• Flash web server

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Processing of HTTP request
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Processing of HTTP request
Data not ready to be read from socket
stat() and open() sys call may block on disk I/O
read() and write() sys call may block too
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Multiple Process - MP

• Each process handles one request
• Disadvantages
• Each process has its separate address space
• Cannot share data separate cache
• Context switch overhead

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Multiple Threads - MT

• Each thread handles one request
• Advantages
• One address space All threads share one cache
• Less context switch overhead
• OS has to support kernel threads
• Apache V2.0 can use threads

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Single Process Event Driven - SPED

• Single thread of execution
• Use non-blocking system calls to perform I/O
  operations
• Used by Zeus web server

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Single Process Event Driven - SPED

• SPED should be able to process many requests at a
  time but
• Non-blocking read/write dont work on disk
  operations

Disk I/O operations still block
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Asymmetric Multi Process Event Driven

• Combination of MP and SPED
• Use non-blocking calls to perform network and
  pipe operations
• Use helper process to perform blocking disk I/O
  operations

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Asymmetric Multi Process Event Driven

• Helper process can be a separate thread or
  process
• Master and Helper process communicate through IPC
• Master and Helper mmap() the same request file
• Helper process reads file from disk and brings
  into memory
• Helper notifies master that file is ready
• Avoid data transfer between processes

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Flash Web Server

• Flash web server implementation of the AMPED
  architecture
• Uses aggressive caching
• Pathname translation caching
• Response header caching
• Caching of already mapped files

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Performance Evaluation

• Compare different web server architecture
• Flash AMPED
• Flash SPED
• Flash MT
• Flash MP
• Apache V1.3.1
• Zeus V1.30

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Test Platform

• Server
• Speed 333 MHz Pentium II
• Memory 128 MB
• Operating System
• Solaris 2.6
• Free BSD 2.2.6 No support for threads
• Clients
• Software that simulates HTTP clients

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Synthetic Workload

• Clients request the same file repeatedly
• Purpose to see how web server behaves under best
  conditions

Solaris
FreeBSD
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Trace Based Experiments

• Replay access logs from real web servers

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Trace Based Experiments

• Test server with workload of different data set
  size

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Trace Based Experiments

• Varying the number of clients

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Conclusion

• Efficient web server Need to handle request and
  perform disk operations
• Web server architecture
• MP/MT
• SPED
• AMPED Combines efficiency of SPED and MP
• Flash web server based on AMPED outperforms Zeus
  and Apache