88 CHAPTER 9: PERFORMANCE MONITORING3 Select Caching Performance Graphs from the available graph types.Select one of the three available time periods, Daily, Weekly, or Monthly,by clicking the appropriate radio button.4 Click OK.The Caching Performance graphs show the following information, whichis updated every 5 minutes: Bandwidth Saving (%)The average percentage of bandwidth savings obtained through theuse of the Webcache. This is calculated as the ratio of bytes served bythe Webcache to total requested bytes. Hit and Miss Rate (%)The percentage of client machine HTTP requests sent to the Webcachethat have been served from the Webcache (a cache hit) and not servedfrom the Webcache (a cache miss). A cache miss requires the contentto be retrieved from the origin server over the Web.A high hit rate indicates more efficient operation, as the Webcache issaving requests from being sent to the Web, which speeds upresponse time and reduces bandwidth use. A reasonable hit rate is40-60%. The hit rate that the Webcache achieves is largely dependantupon: How frequently the same request is made. The hit rate will be lowif there is no revisiting of sites. Caching only works well if the samerequest is made frequently. The smaller the range of requestsmade, the more effective the Webache will be and the higher thehit rate will be. Whether the content provider on the origin web site allows thecontent to be cached or not. Some content providers will preventcertain information from being cached. Whether the content is frequently changed on the origin web site.If so, the copy held on the Webcache must be discarded, and thenew version retrieved. This is treated as a cache miss. Request Rate (sec-1)The average number per second of client machine HTTP requests sentto the Webcache.
