id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
1990	proxy_cache_min_uses not counted per variant on initial requests	chrisd8088@…		"When `proxy_cache_min_uses` is set to a value greater than 1, and multiple requests arrive which all resolve to a common primary `proxy_cache_key` but which are different variants according to the `Vary` response header, the requests are not counted on a per-variant basis at first, until at least one variant is cached.

Suppose `proxy_cache_min_uses 2` is configured and two requests for the same URL arrive with different `Accept-Encoding` headers, and suppose the backend responds to both with `Vary: Accept-Encoding`.

The second request //will// be cached in this case, even though only one ""use"" has so far been seen for that variant.

After this, future requests will be counted on a per-variant basis, however.

Consider the following sequence of requests for the same URL with `proxy_cache_min_uses 2`:

{{{
Accept-Encoding: foo                MISS (not cached)
Accept-Encoding: bar                MISS (cached)
Accept-Encoding: bar                HIT

Accept-Encoding: foo                MISS (not cached)
Accept-Encoding: abc                MISS (not cached)
Accept-Encoding: foo                MISS (cached)
Accept-Encoding: abc                MISS (cached)
Accept-Encoding: foo                HIT
Accept-Encoding: abc                HIT
}}}

So the `foo` variant ends up not cached until its third request, while the `bar` variant is cached on its first request.  Only the `abc` variant is correctly cached on its second request.

This appears to be due to the way that `ngx_http_file_cache_open()` first calls `ngx_http_file_cache_exists()` but only proceeds to `ngx_http_file_cache_read()` if a ""primary"" cache file is found, and it's only in `ngx_http_file_cache_read()` that the variant is tested and a ""secondary"" cache file may be opened instead using `ngx_http_file_cache_reopen()` (see https://hg.nginx.org/nginx/file/stable-1.16/src/http/ngx_http_file_cache.c#l598).

So ""uses"" are counted generically against the primary key, regardless of variation, until a first cache file is created for that key.

It would be ideal if, instead, per-variant use counting could be done from the start for each unique cache key."	enhancement	closed	minor		nginx-core	1.16.x	wontfix			Linux 10-0-1-120 4.19.0-0.bpo.6-amd64 #1 SMP Debian 4.19.67-2+deb10u2~bpo9+1 (2019-11-12) x86_64 GNU/Linux	"nginx version: nginx/1.16.0
built with OpenSSL 1.1.0k  28 May 2019 (running with OpenSSL 1.1.0l  10 Sep 2019)
TLS SNI support enabled
configure arguments: --with-http_stub_status_module --with-http_ssl_module --with-http_gzip_static_module --with-http_realip_module --with-pcre --with-debug --with-http_auth_request_module --with-http_sub_module --with-ipv6 --prefix=/usr --user=www-data --group=www-data --pid-path=/var/run/nginx.pid --lock-path=/var/lock/nginx.lock --conf-path=/etc/nginx/nginx.conf --http-log-path=/var/log/nginx/access.log --error-log-path=/var/log/nginx/error.log --http-proxy-temp-path=/var/lib/nginx/proxy --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-client-body-temp-path=/var/lib/nginx/body"