Cache hit ratio
Cache hit ratio is the percentage of requests that a CDN serves directly from its cache, without fetching the content from the origin server. A high ratio means most viewers get video from nearby edge servers. It is calculated as cache hits divided by total requests.
Why it matters
Cache hit ratio is a direct read on CDN efficiency. A high ratio means faster starts, fewer origin requests and lower origin costs. A low ratio means viewers wait while content is fetched from far away, and the origin carries extra load during traffic spikes. It is one of the first numbers to check when delivery costs climb.
How it works
- Each request to a CDN edge is logged as a hit or a miss.
- A hit means the edge already had the content and sent it directly.
- A miss means the edge fetched it from the origin or a shield first.
- The ratio is hits divided by all requests, shown as a percentage.
What is a good cache hit ratio for video?
A good cache hit ratio for video streaming is generally above 90%, and popular content often reaches higher. Live streams and large long-tail libraries tend to score lower, because new or rarely watched segments are not yet cached. Watching the trend over time is more useful than any single number.
How do I calculate cache hit ratio?
Calculate cache hit ratio by dividing cache hits by the total number of requests, which is hits plus misses. For example, 39 hits and 2 misses gives 39 divided by 41, or about 95.1%. Most CDN dashboards show this figure directly, often split by region or content type.
How can I improve my CDN cache hit ratio?
Improve cache hit ratio by letting segments stay cached longer, removing unneeded query strings from URLs and adding an origin shield. Video segments rarely change, so they can have long cache lifetimes. Keeping URLs consistent across viewers also matters, because each unique URL is cached separately.
Where it's used
OTT services and live sports streamers track cache hit ratio to see how often viewers are served from nearby copies, since a low ratio means slower playback and higher costs.
