1. Performance of Web Proxy Caching in Heterogeneous Bandwidth Environments IEEE Infocom, 1999 Anja Feldmann et.al. AT&T Research Lab 발표자 : 임 민 열, DB lab, CS Dept.

2. Contents Introduction Goal Results Simulation Environment Contribution & Critiques

3. Introduction Web Proxy Caching Improve performance in several ways. General performance metrics. Hit ratio, Byte hit ratio. Estimate the reduction in bandwidth requirements between the proxy and the content provider. Do not reflect the end user perceived latency. Web Server Clients Web Cache LAN Internet

4. Introduction Terminology Heterogeneous bandwidth environments The network speeds between every elements are significantly different Byte hit ratio # of bytes served by a cache # of bytes sent to clients Cookie The method of customizing resources on a per-user basis Connection cache The method of maintaining persistent connections with other system and re-use them

5. Goal Evaluate the performance effects of factors that cannot be modeled using high-level metrics. Heterogeneous bandwidth. Aborted connections. HTTP headers that may affect cacheability of resources. Persistent TCP connections.

6. Results Summary Heterogeneous bandwidth environments Can negate any bandwidth savings from a proxy caching. Aborted connections The bandwidth consumption may increase. Persistent TCP connections The benefits of using it between clients and the proxy can outweigh the benefits of caching documents. Data cache & Connection cache. HTTP headers with a cookie Inappropriate to cache HTTP 1.0 resources that have cookies Roughly 30% of requests have cookies.

7. Simulation Environment Develop a web proxy cache simulator, PROXIM. Workload Modem trace Access patterns by subscribers to a commercial ISP, connected through slow model lines. Internet Proxy Cache Content Provider Trace Collector Content Provider Modem Bank Dialup Client

8. Simulation Environment Research trace Access patterns from a research community connected to the Internet via a high-speed link. Trace collector TCP & HTTP events : Timestamps, sequence number, etc. HTTP headers. Byte counts. Internet Proxy Cache Content Provider Trace Collector Content Provider Fire wall Workstation

9. Simulation Environment Three simulation scenarios (a). Using a proxy. (b). Without a proxy, where the bandwidth to the client is the bottleneck. (c). Without a proxy, where the bandwidth on the network connection the clients to the Internet is the bottleneck.

10. Simulation Environment Simulator Cache LRU replacement algorithm Sufficiently large cache size Network connection Idle connection to give a persistent connection Document transfer Use modem queue & network queue Latency calculation Use timestamp

11. Performance effects of the proxy Hit ratio The number of HTTP requests that are uncacheable Case 1 : The proxy ignore cookies Modem trace : 54%, Research trace : 33.9% Case 2 : The proxy take cookies into account Modem trace : 35.2%, Research trace : 27.0%

12. Performance effects of the proxy Bandwidth Consumption Model the system behavior when requests are aborted Frequency of interrupted transfers in workload 10.94% Case 1 : The proxy continues the download Measure the total number of bytes received by the clients With the proxy : 49.8 GB, Without the proxy : 58.7 GB Case 2 : The proxy abort the download immediately

13. Performance effects of the proxy Latency comparison 4 cases No proxy Proxy using data caching mechanism Proxy using connection caching mechanism Proxy using both mechanisms Case 1 : Modem trace

14. Performance effects of the proxy Case 2 : Research trace Main observations The two types of caching are complementary and should be used together. It is important to manage aborted connection well. More study is needed into effective ways to cache documents with cookies.

15. Contribution & Critiques Analyze real workload Try to model the benefits of proxy caching exactly using low-level missing factors Aborted connections Excellent, detailed simulation Based on HTTP/1.0 protocol, not 1.1

16. References Web Protocols and Practice, Addison-Wesley, 2001