4 Replies Latest reply: Oct 13, 2012 12:59 PM by Regis RSS

    Web Cache Efficiency hits and misses

    chisro

      I am curious if anyone can explain the hits and misses concept. I am looking at the web cache statistics on my web gateway v7.2 and wanted to know:

       

      1. what do the hits and misses mean?

      2. what are the best practices for these processes?

      3. should the hits and misses be exactly the same?

      I didnt find anything in the users guide, so I thought I would put the question out to you guys.

      thanks in advance!

        • 1. Re: Web Cache Efficiency hits and misses
          Folcan

          Hello,

           

          Web Cache Efficiency shows how numbers of caching requests evolved during the interval that was selected for the summary and sorts them into hits and misses.

          Hits : How many requests have been cached

          Missed : How many requests have NOT been cached

           

          Some websites have a special directive in theire headers like :

              header('Pragma: no-cache');

              header('Expires: 0');

              header('Cache-Control: no-cache, must-revalidate');

           

          That say : "please do not use the cache to load the web page".

          For exemple, Google gmail use this headers to view the most recents mails.

           

          Should the hits and misses be exactly the same?

          Probably not, depend on wich website you visit.

          • 2. Re: Web Cache Efficiency hits and misses
            chisro

            thank you!

            • 3. Re: Web Cache Efficiency hits and misses
              trishoar

              Folcan wrote:

               

              Hello,

               

              Web Cache Efficiency shows how numbers of caching requests evolved during the interval that was selected for the summary and sorts them into hits and misses.

              Hits : How many requests have been cached

              Missed : How many requests have NOT been cached

               

              Lets be clear on this

              Hits: How many objects have been vended from cache

              Misses: How many objects have not been vended from cache

               

              This should give you an idea as to how much bandwith has been saved by the caching, as objects vended from cahce did not need to be fetched from to origin web server.

               

              Tris

              • 4. Re: Web Cache Efficiency hits and misses
                Regis

                This won't be helpful to your question, but while on the topic of web cache, I've had to disable it.  It was causing enormous load and latency to our appliances.   This has to be a bug because 3 year old far far more anemic Bluecoat boxes struggled with raw throughput of our user profile but never cut a sweat doing the caching.   Those were awful little single core cpu boxes, and nothing like these rather beefy WBG-5000-B boxes we have at this site.   This site is around 600 users and we split them among a pair of those.   We'd see  load averages in top of like 20 or more sometimes on one of the appliances and latency would slow annoyingly.   Turned off caching and the difference was amazing.

                 

                If you're not terribly bandwidth constrained and the caching isn't buying you a ton, keep this in the back of your mind if you see load issues.

                 

                We're on 7.2.0.1 on these boxes fwiw.