What is the cache hit ratio?

The cache hit ratio is the share of requests a cache answers from storage, out of all the requests it could have cached. A higher ratio means fewer requests reach the origin and more visitors get a fast response. CDNs report it per zone or distribution, and sometimes per PoP or per URL.

hit ratio = hits / (hits + misses)

9,000 hits, 1,000 misses -> 90%

What lowers it:

• A cache key or `Vary` that splits one page into many entries.
• Short TTLs, which expire entries before they are reused.
• Purges, which empty the cache all at once. Right after a deploy, the ratio for the purged pages is zero until visitors or a warmer fill them again.
• Low traffic per page per PoP. An object requested rarely in one region is often evicted before it is reused.

A site-wide average hides the post-deploy dip. Look at the hit or miss of your important pages right after a purge, which is what cache warming changes.