-1. Make sure that your website or application is integrated with CDN successfully: the static content is delivered through a custom domain, the custom domain is set up correctly.
-2. Make sure that more than 2 days have passed since you have started to use CDN.
-3. Deliver more content through CDN, if possible.
+A high cache hit ratio shows the efficiency and practicality of using CDNs. The higher it is, the better. By reducing the number of times CDN edge servers request a file from the source, you improve performance, reduce the load on the source, and reduce outbound traffic costs.
-If you already set up CDN delivery for all possible static content, but the cache hit ratio remains low, revise the CDN resource’s cache settings:
+## Issues with the low cache hit ratio
-## CDN Caching option
+A low cache hit ratio is a sign of something going awry, and shows that many requests are proxied to the origin instead of files being delivered from the cache.
-
-
-Check if this option is added and activated. If you use this option with Origin controlled parameter make sure that origin settings are suitable for caching.
-
-CDN caches according to Cache-Control headers from your origin.
-
-**Note**: Cache-control directives that are not suitable for CDN: no-cache, no-store, private, max-age=0
-
-## Query-String and Set-Cookies options
-
-
-
-CDN caches content with different query-strings and Set-Cookie headers separately by default If you have such content on your website or application, we recommend you to use Ignore Query-String and Ignore Set-Cookies options for the CDN-resource. It will help to decrease the number of requests from CDN to the origin server and increase the Cache hit ratio.
-
-## Large Files Delivery Optimization
-
-
-
-Use the Large Files Delivery Optimization option for the large content caching. You may know more about the option from the article.
-
-If you add any parameters (for example, a unique signature for users) to the URL, but not as a query string (```http://cdn.example.com/image.jpg?id=1```), it requires custom caching keys set up.
-
-Contact [technical Support](mailto:support@gcore.com) for manual settings and describe the URL scheme: which parts should be cached and which – should not.
\ No newline at end of file
+A low cache hit ratio can be accompanied by low content delivery speed Compare the request scheme for cached file ```User → CDN edge → User``` with uncached—```User → CDN edge → Origin → CDNedge → User```. In the second case, more requests go to the origin, which causes longer response time simply due to a higher distance and more hops in the sequence.
+
+## Check if slow content delivery is related to low cache hit ratio
+
+1\. Check Statistics for “Cache hit ratio.” If it is low (less than 80% in most cases), also check “Traffic” and “Requests” to avoid misconceptions in determining the cause. You can learn more about where and how to view reports in the guide about viewing statistics of CDN resources.
+
+**Note**: 80% is an approximate number, used for descriptive purposes, the accurate number highly depends on the use-case.
+
+2\. Check the response headers using the ```curl -I``` command; for instance:
+
+```
+curl -I cdn.example.com/assets/sample-image.png
+```
+
+**Note**: Request content from one specific CDN edge server.
+
+| Value | +Meaning | +
| Cache-Control: max-age=0 | +This value prohibits content caching. It may cause an issue with the Cache hit ratio and reduce performance. However, in some cases, this value is ok. |
+
| Cache-Control: no-cache | +|
| Cache-Control: no-store | +|
| Cache-Control: private | +This value caches content only in users’ browsers, not the edge servers’ cache.
+ +Note: If the request contains custom headers starting with X (e.g., “X-custom-header”), the CDN will treat the request as a new request and forward it to the origin (as with cookies.) |
+
| Cache: MISS | +This value specifies that the response is received from the origin, bypassing the cache. Our CDN caches files on the first request. This means that the first request for a file will result in MISS (CDN had to reach the origin to pull the resource and cache it locally) and every following request for the same file will result in HIT (served from a local CDN cache.) |
+
| Cause | +Solution | +
| Traffic started less than two days ago, and more cache needs to be collected. | +Traffic patterns and amounts dictate how long you should wait to populate the cache. Usually, waiting for around 48 hours after the CDN integration is enough to cache most resources, but the exact time is individual. You can also deliver more content through CDN. |
+
| Content is not requested enough, and the cache per server is low. | +Increase the traffic to your content or use the paid Origin shielding option to accumulate requests. | +
| A “Cache-Control” value prohibits the CDN from caching content. | +Ensure that the CDN Caching option is enabled and configured in the following way.
+
|
+
| Responses contain query strings or a Set-Cookie header, so the files are cached as different. | +Enable Ignore Query String and Ignore Set Cookie options. Then, a single file will be delivered from the cache, regardless of the request parameters and the Set Cookie header. | +
| The Vary header is set on origins so that content is cached suboptimally. | +Change the Vary header settings on your origin. | +