Question on the Current Cache Hit Ratio log messages in dispatcher logs | Community
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ToddRowan
Level 1
December 2, 2020

Question on the Current Cache Hit Ratio log messages in dispatcher logs

  • December 2, 2020
  • 2 replies
  • 3452 views

I recently learned about the Current cache hit ratio log message in dispatcher logs. 

 

But I can't find any good documentation on it. So I have a few questions:

  1. Over what timeframe is the ratio calculated? Is it from Apache startup?
  2. Does the calculation ignore those paths that are configured to never cache in the dispatcher?

I ask because I have an existing access log query that calculates the difference between dispatcher requests and publish instance requests only on paths where I know there is caching. I ignore servlet paths that do no caching, and I also ignore all requests other than 200s. With that calculation I get a higher hit ratio than what the dispatcher claims. 

 

How much should I trust the dispatcher log calculation?

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    2 replies

    SureshDhulipudi
    Community Advisor
    SureshDhulipudiCommunity Advisor
    Community Advisor
    December 3, 2020

    Cache Hit Ratio: This means your fetching from render level vs from cache is measured.  You want to hit 80+ percent from cache, and you should follow the help here:

    https://helpx.adobe.com/experience-manager/kb/optimizing-the-dispatcher-cache.html

     

    For common dispatcher log details:

    https://helpx.adobe.com/experience-manager/kb/ams-dispatcher-manual/common-logs.html

     AMS Dispatcher Manual

    https://helpx.adobe.com/experience-manager/kb/ams-dispatcher-manual.html

     

      T
      ToddRowanAuthor
      Level 1
      December 3, 2020
      Yes, I've seen all that. None of this answers any of my questions.
        joerghoh
        Adobe Employee
        joerghohAdobe Employee
        Adobe Employee
        December 3, 2020

         

        The ratio is calculated as (100 * req_hits / req_total) with

         

        req_hits = # files delivered from cache

        req_total = the total number of requests handled by the dispatcher

         

        from this point of view the cache-hit ratio is the same if requests are blocked on dispatcher (not httpd!) or forwarded to publish. So the number is nice, but it's hard to draw meaningful conclusions from it.

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