Debugging Nginx Cache Misses: Hitting high number of MISS despite high proxy valid

[Quintin Par]

My proxy cache path is set to a very high size

proxy_cache_path  /var/lib/nginx/cache  levels=1:2
 keys_zone=staticfilecache:180m  max_size=700m;
and the size used is only

sudo du -sh *
14M cache
4.0K    proxy
Proxy cache valid is set to

proxy_cache_valid 200 120d;
I track HIT and MISS via

add_header X-Cache-Status $upstream_cache_status;
Despite these settings I am seeing a lot of MISSes. And this is for pages I
intentionally ran a cache warmer an hour ago.

How do I debug why these MISSes are happening? How do I find out if the
miss was due to eviction, expiration, some rogue header etc? Does Nginx
provide commands for this?

- Quintin
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