nginx缓存命中率统计

nginx提供了$upstream_cache_status这个变量来显示缓存的状态，我们可以在配置中添加一个http头来显示这一状态，达到类似squid的效果。 

Java代码  

location  / {
    proxy_redirect          off;
    proxy_set_header        Host            $host;
    proxy_set_header        X-Real-IP       $remote_addr;
    proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_connect_timeout   180;
    proxy_send_timeout      180;
    proxy_read_timeout      180;
    proxy_buffer_size       128k;
    proxy_buffers           4 128k;
    proxy_busy_buffers_size 128k;
    proxy_temp_file_write_size 128k;
    proxy_cache cache;
    proxy_cache_valid 200 304 1h;
    proxy_cache_valid 404 1m;
    proxy_cache_key $uri$is_args$args;
    add_header  Nginx-Cache "$upstream_cache_status";
    proxy_pass http://backend;
}

Java代码  

HTTP/1.1 200 OK
Date: Mon, 22 Apr 2013 02:10:02 GMT
Server: nginx
Content-Type: image/jpeg
Content-Length: 23560
Last-Modified: Thu, 18 Apr 2013 11:05:43 GMT
Nginx-Cache: HIT
Accept-Ranges: bytes
Vary: User-Agent

为了能够统计缓存的命中率，我们需要在日志中记录这一状态 

Java代码  

log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                  '$status $body_bytes_sent "$http_referer" '
                  '"$http_user_agent" "$http_x_forwarded_for"'
                  '"$upstream_cache_status"';

统计方法：用HIT的数量除以日志总量得出缓存命中率： 

Java代码  

awk '{if($NF=="\"HIT\"") hit++} END {printf "%.2f%",hit/NR}' access.log
30.15%

$upstream_cache_status包含以下几种状态： 
・MISS 未命中，请求被传送到后端 
・HIT 缓存命中 
・EXPIRED 缓存已经过期请求被传送到后端 
・UPDATING 正在更新缓存，将使用旧的应答 
・STALE 后端将得到过期的应答