Understanding Cache Effectiveness

Whenever a request reaches a Varnish Cache instance, one of four outcomes occurs: hit, miss, pass, or synth.

A key metric when evaluating website performance is cache hit rate. Cache hit rate is a measure of how effectively the cache is responding to customer requests.

A hit means that the cache responded to the request with a cached resource.

A miss means that the cache tried to respond to the request with a cached resource but could not do so because it did not have a copy of the requested resource in its memory.

A pass means that the cache did not even try to look up a response for the requested resource — often users specifically instruct Varnish Cache to pass on urls that should never be served from cache like /checkout, but there are other causes as well.

From a performance standpoint, the goal is to increase Hit % and decrease Miss and Pass %.

Why do you care?:

Whenever the cache answers a customer request, that means the request did not need to be answered by your website origin server. Having a large percentage of cache hits results in performance benefits and reduced costs.

From a performance standpoint, Varnish Cache’s quick lookup and response time combined with the geographic distribution of Section’s platform means that your users are quickly served a response from a server close to their geographical location.

This improves time-to-first-byte and keeps latency low.

From a cost-savings perspective, every request that receives a response from cache does not need to connect to your origin server, greatly reducing load. With a finely-tuned caching configuration, your origin only needs to respond to requests for personalized actions such as checkout and and account pages.

How do you see it?:

This is the first chart we show you on the Section dashboard. To see this in action on our demo bootcamp application, go to Section Bootcamp Overview dashboard.

For more detailed information, such as the absolute number of requests and size of those requests, you can view Trending Metrics. For more in-depth guidance on using our Monitoring tools, see the monitoring section of our documentation.