Integrating Web Caching And Web Pre Fetching
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Integrating Web Caching and Web Prefetching In Client-Side Proxies
Objective
The motivation for our project is to design an innovative cache replacement algorithm, not only considering the caching effect in the Web environment, but also evaluating the prefetching rules provided by various prefetching schemes.
Introduction (Cont.) Purpose •
Reduce user perceived latency
Key Issue •
Efficiently predict and fetch the future URLs likely to be visited by the user in advance Efficient prediction algorithms
Cost •
Increased network and server load due to errors in prediction Appropriate threshold value
Web caching
Web Caching : Satisfying user Web requests by servers other than original Web servers publishing the requested Web objects 1. 2. 3.
Latency, External traffic, Load on web servers and routers.
Deployed at: Corporate network boundaries, ISPs, Web Servers, etc.
Web Cache
Browser
Browser Cache
Client
Browser
Web Server
Centralized Web Cache Browser Cache
Client Corporate LAN
Internet
Web caching
Benefits:
Improves web performance (reduces access latency) Increases web capacity Alleviate traffic congestion (reducing network bandwidth consumption) Reducing number of client requests (workload) Possibly improve failure tolerance and robustness of Web (maintaining cached copies of web objects for unreachable networks)
Web Prefetching •
Prefetching- caches web objects in anticipation of users’ future needs Focuses on making cache-related storage capacity decisions (storage capacity limits the number of prefetched web objects)
Therefore allocate cache storage in prefetching
Categories •
DNS Prefetching
•
Connection Prefetching
•
Web client initiate the name resolution process in advance of the user’s request Set up TCP connection before the user’s request Timing issue is important
HTTP Prefetching
Web client issuing HTTP request in advance and cache the response
Web prefetching techniques
Client-initiated policies User A is likely to access URL U2 right after URL U1
Server-initiated policies Anticipate future requests based on server logs and proactively send the corresponding Web objects to participating cache servers or client browsers Hybrid policies Combine user access patterns from clients and general statistics from servers to improve the quality of prediction
Who Initiates the Prefetching
Server Side Prefetching •
•
Uses information from the web server to predict the documents that will be requested soon Prefetch the object from the disk to the main memory of the server Provides hints to the client to improve the client’s response time The client then can initiate a prefetch
Who Initiates the Prefetching (Cont.) Proxy Side Prefetching
Proxy prefetches documents from web servers and stores in proxy cache Proxy can gather information from multi-client to multiserver, makes it possible to do good prediction
Who Initiates the Prefetching (Cont.) Client Side Prefetching • • •
Works with browser Learns the personal profile and predicts future requests Uses the available bandwidth to retrieve documents when the user is stop to read web contents
Modules •
System environment
•
Cache replacement algorithm
•
System model Prefetching rule
Normalized profit function Algorithm IWCP
Performance analysis
Impact of cache capacity Impact of confidence threshold Execution overhead
module1
•
System environment
System model Prefetching rule
Log
-
request
request
Response + hint
response Web Client
Prediction Engine
Proxy server
Request Processing module
Web object depository
System model of web prefetching and web caching
Prefetching rule repository
Web server
Prefetching rule
Rule1: A prefetching rule is an implication of the form o1,..,oi c oi+1 where o1,..,oi , oi+1 Є O and o1,..,oi , oi+1 is an access sequence in D and c is the confidence of the prefetching rule
Rule2: The confidence c of the prefetching ruleo1,..,oi c oi+1 is a conditional probability of p(o1,..,oi , oi+1 )/ p(o1,..,oi )
An object oi+1 is referred to as an implied object if and only if the prefetching rule is triggered by some client who has already referenced the objects in precedent request.
Hybrid Prefetching-System Model System model of prefetching proxy
System Specification:
Hardware Specification: Processor Type : Pentium -IV Speed : 1.2 GHZ Ram : 128 MB RAM Hard disk : 20 GB HD Software Specification: Operating System : Linux,Win2000 Pgm Package : JAVA / J2EE Protocol : HTTP. Web Server : Apache Tomcat 5.0
Objective
The motivation for our project is to design an innovative cache replacement algorithm, not only considering the caching effect in the Web environment, but also evaluating the prefetching rules provided by various prefetching schemes.
Introduction (Cont.) Purpose •
Reduce user perceived latency
Key Issue •
Efficiently predict and fetch the future URLs likely to be visited by the user in advance Efficient prediction algorithms
Cost •
Increased network and server load due to errors in prediction Appropriate threshold value
Web caching
Web Caching : Satisfying user Web requests by servers other than original Web servers publishing the requested Web objects 1. 2. 3.
Latency, External traffic, Load on web servers and routers.
Deployed at: Corporate network boundaries, ISPs, Web Servers, etc.
Web Cache
Browser
Browser Cache
Client
Browser
Web Server
Centralized Web Cache Browser Cache
Client Corporate LAN
Internet
Web caching
Benefits:
Improves web performance (reduces access latency) Increases web capacity Alleviate traffic congestion (reducing network bandwidth consumption) Reducing number of client requests (workload) Possibly improve failure tolerance and robustness of Web (maintaining cached copies of web objects for unreachable networks)
Web Prefetching •
Prefetching- caches web objects in anticipation of users’ future needs Focuses on making cache-related storage capacity decisions (storage capacity limits the number of prefetched web objects)
Therefore allocate cache storage in prefetching
Categories •
DNS Prefetching
•
Connection Prefetching
•
Web client initiate the name resolution process in advance of the user’s request Set up TCP connection before the user’s request Timing issue is important
HTTP Prefetching
Web client issuing HTTP request in advance and cache the response
Web prefetching techniques
Client-initiated policies User A is likely to access URL U2 right after URL U1
Server-initiated policies Anticipate future requests based on server logs and proactively send the corresponding Web objects to participating cache servers or client browsers Hybrid policies Combine user access patterns from clients and general statistics from servers to improve the quality of prediction
Who Initiates the Prefetching
Server Side Prefetching •
•
Uses information from the web server to predict the documents that will be requested soon Prefetch the object from the disk to the main memory of the server Provides hints to the client to improve the client’s response time The client then can initiate a prefetch
Who Initiates the Prefetching (Cont.) Proxy Side Prefetching
Proxy prefetches documents from web servers and stores in proxy cache Proxy can gather information from multi-client to multiserver, makes it possible to do good prediction
Who Initiates the Prefetching (Cont.) Client Side Prefetching • • •
Works with browser Learns the personal profile and predicts future requests Uses the available bandwidth to retrieve documents when the user is stop to read web contents
Modules •
System environment
•
Cache replacement algorithm
•
System model Prefetching rule
Normalized profit function Algorithm IWCP
Performance analysis
Impact of cache capacity Impact of confidence threshold Execution overhead
module1
•
System environment
System model Prefetching rule
Log
-
request
request
Response + hint
response Web Client
Prediction Engine
Proxy server
Request Processing module
Web object depository
System model of web prefetching and web caching
Prefetching rule repository
Web server
Prefetching rule
Rule1: A prefetching rule is an implication of the form o1,..,oi c oi+1 where o1,..,oi , oi+1 Є O and o1,..,oi , oi+1 is an access sequence in D and c is the confidence of the prefetching rule
Rule2: The confidence c of the prefetching ruleo1,..,oi c oi+1 is a conditional probability of p(o1,..,oi , oi+1 )/ p(o1,..,oi )
An object oi+1 is referred to as an implied object if and only if the prefetching rule is triggered by some client who has already referenced the objects in precedent request.
Hybrid Prefetching-System Model System model of prefetching proxy
System Specification:
Hardware Specification: Processor Type : Pentium -IV Speed : 1.2 GHZ Ram : 128 MB RAM Hard disk : 20 GB HD Software Specification: Operating System : Linux,Win2000 Pgm Package : JAVA / J2EE Protocol : HTTP. Web Server : Apache Tomcat 5.0
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