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Active Cache : Caching Dynamic Contents on the Web

Pei Cao, Jin Zhang and Kevin Beach

Middleware’98

2000. 10. 12

SSLAB, EE Dept, KAIST

박상호

Comment: 서버 쪽에서 해야할 일들을 proxy 로 이동시키는 방법에 대한 논문 .아이디어가 기발한 것 같진 않지만 , 사용 가능한 application 을 찾아 명시하였고 , 자바를 이용한 방법을 제시하였다 .

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Content

▣ Introduction

▣ Active cache protocol

▣ Security Mechanism

▣ Resource Management Policy

▣ Implementation

▣ Performance

▣ Conclusion and critique

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Introduction

▣ Caching in the Web◈ Inability to cache dynamic documents

▣ Active cache

◈ Migrates parts of server processing to the caching proxy

◈ Cache applet : server-supplied code written in JAVA

ServerProxy

request

reply

processing

ServerProxy

processing

request

reply

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Active cache protocol(1/2)

◈ New entity header : CacheApplet– CacheApplet: code=“code.class”, archive=“code.jar”, codebase=“codebase_url”

◈ Active-Cache enabled proxy – Applet’s execution failure : the request is sent to the server

– Applet’s execution success : send the cached document or new document to the client

– Send the log object back to the server periodically

Server/test.html

Server/test.html

test.html -> test.classServer/test.html With CacheApplet entity header

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Active cache protocol(2/2)

▣ Active cache interface

Cache hit

FromCache()

1:new content0:cached content-1:forward the request to server

ActiveProxy class : File access, cache query, Lock/unlock, sending requests to servers

Available : java.util, java.text, java.math, java.security, java.sql, ActiveProxy class

Unvailable : java.io, java.lang, java.systems

Proxy :

CacheApplet :

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Cache Applet Examples(1/2)

▣ Logging User Accessespublic static int FromCache(string User_HTTP_Request,string Client_IP_Address,string Client_Name,int Cache_File,int New_File) {

int fd = open(“logapplet.log”, APPEND_ONLY);int status = lock(fd);string date = new curtime();log_to_file(fd, date, Client_Name, User_HTTP_Request, Client_IP_Address);status = unlock(fd);close(fd);

return(0); // 0 means use the cached file}

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Cache Applet Examples(2/2)

▣ Advertising Banner Rotation

▣ Access Permission Checking

▣ Client-Specific Information Distribution

▣ Server-Side Include Expansion

▣ Delta Compression

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Security Mechanisms

▣ Two types of security attacks◈ An applet’s illegal access to information belonging to

other web server– JAVA : built-in security mechanism

– Applets from different servers do not cooperate

– Static examination of the classes and functions

◈ Denial-of-service attacks : resource consumption– Storage size

– Disk bandwidth

– Network bandwidth

– CPU usage

– Virtual memory size

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Resource Management Policies

▣ Proxy decide whether an object should be cached◈ Based on the proxy’s estimation of the benefits and the

cost of caching– Benefit : saved network bandwidth

– Cost : storage cost, CPU cost, network communication(send_request_to_server calls)

◈ Cost-aware cache replacement algorithm

◈ Negotiated object : server specifies the estimated costs and desired duration of caching

◈ Un-negotiated object

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Implementation

▣ Implementation◈ CERN httpd proxy

– CacheApplet header

– Invoke the applet

◈ setrlimit() system call

◈ Sending the log object : HTTP POST

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Performance(1/2)

▣ Applet overhead◈ WebStone 2.0

◈ 6 applets : null, log, ads, apc, ssi, clid

◈ Server(SPARC 20), proxy(99MHz Intel x86)

Proxy 1 client 10 clients 20 clients

null 1.47 1.75 1.73

log 2.16 2.31 2.24

ads 1.40 2.44 3.23

apc 2.50 2.73 2.72

ssi 3.81 4.00 3.80

csid 1.06 2.04 2.23

Response time(active cache)

Response time(the original CERN httpd proxy)

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Performance(2/2)

▣ Internet traffic reduction through active cache◈ AT&T WorldNet Internet Service Provider

– 30% of all user request carry cookies

– AT&T traces– 35% hit ratios and 30% byte hit ratios

– Active cache : 55% hit ratios and 41% byte hit ratios

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Conclusion and critique

▣ Conclusion◈ Support caching of dynamic documents on the Web

◈ Protocol design, interface, security mechanism and resource management strategies

▣ Critique◈ Bad performance

– Increase the number of web server instead of using proxy

◈ Difficult to program– Servlet or jsp

◈ Cache applet restriction