Cache hit ratio is the most direct measure of how well a CDN is working for your content. CHR = (cache hits) / (cache hits + cache misses). A CHR of 95 % means 5 % of requests reach origin; a CHR of 80 % means 20 % do. For VOD streaming, a healthy CHR sits between 95 % and 99 %. For live, where every viewer wants fresh manifests, the manifest CHR is lower (50–80 %) and the segment CHR is high (95 %+).
CHR has two dimensions worth tracking. Edge CHR is what the closest POP to the viewer reports — the share of requests it served from local SSD. Origin CHR is what origin sees — the share of incoming requests it had to answer. With tiered caching, these can differ significantly: edge CHR might be 92 %, but with a shield catching most of the misses, origin CHR (from origin's perspective: requests handled / requests received) is 99 %+.
Improving CHR is a finite-game engineering problem. The standard levers are: longer TTLs on stable content (segments rarely change, so TTL of months is fine), consistent URLs (don't include a session ID in segment URLs — every viewer gets their own cache entry), shielding (consolidate misses), and cache warming (prefetch popular content to all edges before viewers arrive). A 1-percentage-point CHR improvement on petabytes of traffic per month moves real money on CDN bills.
