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World Wide Web Caching: Trends and Technology. Greg Barish and Katia Obraczka USC Information Science Institute IEEE Communications Magazine, May 2000 Presented By: Ossama M. Younis Ph.D. Student, Purdue University. Presentation Outline. Introduction Limitations and problems

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world wide web caching trends and technology

World Wide Web Caching: Trends and Technology

Greg Barish and Katia Obraczka

USC Information Science Institute

IEEE Communications Magazine, May 2000

Presented By: Ossama M. Younis

Ph.D. Student, Purdue University

presentation outline
Presentation Outline
  • Introduction
  • Limitations and problems
  • Desirable properties of a Web Caching system
  • Cache deployment options
  • Design techniques
  • Caching architectures
  • Load balancing and Content-based routing
  • Conclusion
  • What is Web Caching ?
    • Introducing proxy servers at certain points in the network that serve in caching Web documents for faster client access.
    • Comparable to the cache memory in a computer system.
  • Why is it needed ?
    • Rapid growth in HTTP traffic to form the largest part of the Internet traffic which causes more network congestion and server unavailability.
    • The number of Web static pages almost doubles every year.
the expected gains
The Expected gains:
  • Bandwidth saving
  • Improving content availability.
  • Improving web server availability.
  • Reducing network latency.
  • Server load balancing.
  • Improving user’s perception about network’s performance.
main issues and problems
Main Issues and Problems
  • Caching system architecture
  • Proxy placement
  • Caching contents
  • Proxy cooperation/Data sharing
  • Cache resolution/Routing
  • Prefetching
  • Cache placement/Replacement
  • Cache coherency
  • Security and legal ethics of caching
  • Control information distribution
desirable features
Desirable Features:
  • Fast access
  • Robustness
  • Transparency
  • Scalability
  • Efficiency
  • Adaptivity
  • Stability
  • Load balancing
  • Dealing with heterogeneity
  • Simplicity
cache deployment options
Cache Deployment options
  • Near the content consumer
    • Better response time
    • Local service of requests
  • Near the content provider
    • Improves access to logical sets of data
    • Problem: critical to delay sensitive content
    • Problem: security constraints
  • At strategic points in the network
    • Problem with administrative control
  • Caching on a per-user basis
    • Uses the user’s local file system
design techniques
Design Techniques
  • Main Concerns:
    • Speed
    • Reliability
    • Scalability
  • Main design techniques:
    • Hierarchical caching
    • Intercache communication
  • Other design issues
hierarchical caching
Hierarchical Caching
  • Caches are arranged in a tree-like structure
  • A child cache can query parent caches and other siblings
  • A parent cache can never query children
  • This maintains information gradually filtering down to the leaves
  • To avoid swamping parents with information, clustering may be applied to hierarchies.
intercache communication
Intercache Communication
  • Multiple Distributed Caches in meshes
  • Improves scalability, availability, and physical locality
  • Protocols:
    • ICP (Internet Cache Protocol) [Squid]: Caches issue queries to other caches to determine the best location of object retrieval. Main problem is the message overhead
    • CRP (Content Routing Protocol): ICP with multicast feature to query cache meshes
    • Cache digests [Squid]: summarizes cache objects
intercache communication11
Intercache Communication
  • Protocols (cont.)
    • WCCP (Web Cache Communication Protocol) [Cisco]: Enables transparent redirection of HTTP traffic to Cisco Cache Engine
    • CARP (Cache Array Routing Protocol) [Microsoft]: Uses Hashing Schemes for location determination of the required proxy having the requested information
other design issues
Other Design Issues
  • Hash-Based request routing
    • Maps a key (such as the url) to a cache within a cluster
    • Reduces (eliminates) the need of caches to query each other
  • Optimized disk I/O
    • Improves spatial locality
    • Use in-memory data structures to avoid disk I/O
  • Microkernel O.S.
    • Designed to optimize cache performance (resource alloction, task execution, disk access, and transfer time)
more design issues
More Design Issues
  • Content prefetching
    • Local based
    • Server-hint based
  • Implementation:
    • Between clients and servers
    • Between clients and proxies
    • Between proxies and servers
  • Improvements:
    • Less latency (from 26% improvement to 57%)
    • Improved access time
more design issues14
More Design Issues
  • Cache coherency (consistency)
  • Strong consistency techniques:
    • Client polling (If-Modified Since)
    • Invalidation callbacks
  • Weak consistency techniques
    • TTL and Adaptive TTL
    • Piggyback Invalidation
caching architectures
Caching Architectures
  • Proxy Caching
    • Deployed at the edges of the network
    • Unavailable cache  Unavailable network
    • Single point of failure
    • User browser manual reconfiguration in times of failure
caching architectures16
Caching Architectures
  • Reverse Proxy Caching
    • Placing proxies near the content provider
  • Transparent Caching
    • Eliminates the needs to manually configure web browsers
caching architectures17
Caching Architectures
  • Adaptive Web Caching
    • Uses distributed cache meshes to solve the hot spot problem
    • Caches dynamically join and leave the groups based on content demand
    • Administrative boundaries must be relaxed
  • Push Caching
    • Keep data close to those clients requesting this information
    • Assumption: we are able launch caches that may cross administrative boundaries
    • Incurs cost (storage and transmission)
caching architectures18
Caching Architectures
  • Active Caching
    • Applies caching to dynamic documents
    • 30 % of client HTTP requests contains cookies
    • The servers provides the cache with the objects and any associated cache applets
load balancing and content based routing
Load Balancing and Content Based Routing
  • Main goal: Improving performance and scalability
  • Local load balancing: Incoming requests are intercepted and redirected to one member of a group of servers or caches, all of which exist in the same geographic area. This can be achieved by using L4 or L5 switches.
  • Global Load balancing: Instead of distributing requests among members of a local group, requests are distributed to servers or caches which are near the client, to achieve lower network latencies.
  • Examples: Cisco’s WCCP, Distributed Director, DFP, etc.
  • In this paper, the main web caching techniques, design issues, and architectures are discussed.
  • The paper doesn’t compare any of these techniques in terms of scalability, availability, or performance.
  • Some major issues were not addressed:
    • Content security
    • Handling more complex objects and real-time data