ERCIM News No.41 - April 2000 [contents]

Eliminating the I/O bottleneck from World Wide Web Proxies

by Evangelos P. Markatos

World Wide Web proxies are being widely used today, in order to reduce network traffic, web server load, telecommunication costs, and to provide Internet access to users behind a firewall. Web proxies are typically required to handle a heavy load which reaches up to millions of requests per day. To make matters worse, this load is expected to increase sharply in the near future when users will be able to connect to the Internet via fast modems. A research team at ICS-FORTH investigates methods to enhance the performance of Web proxies thus enhancing web server performances.

Although the network bandwidth has been traditionally thought to be the main bottleneck in a proxy’s performance this is not true anymore. Recent research results suggest that a proxy server may spend a significant percentage of its time on file-system related activities.

Experimental evaluation of the web proxy at Digital Palo Alto firewall revealed that the disk I/O overhead of caching turns out to be much higher than the latency improvement from cache hits. Thus, to save the disk I/O overhead the Digital Palo Alto proxy server is typically run in its non-caching mode. This disk I/O overhead can be partially attributed to the fact that file systems were designed and optimized for an every-day pattern of use that is completely different from the needs of a web proxy:

Thus, traditional file system technology can not keep up with the disk I/O needs of busy web proxies. Our current work focuses on identifying and eliminating the sources that create the disk I/O bottleneck. We investigate the effects of storage management policies for web proxies based on the following principles:

We have started testing our approach using a combination of experimental evaluation and simulation. Our initial results are very encouraging: they suggest that our method breaks through the I/O bottleneck and effectively improves performance over traditional proxies (like SQUID) by more than an order of magnitude.


Please contact:
Evangelos P. Markatos – ICS-FORTH
Tel: +30 81 391655
E-mail: markatos@ics.forth.gr