caching - Nginx cache lock always causes 500ms delay -


nginx cache locked requests(http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_cache_lock) takes 500ms respond

$ab -n 2 -c 2 http://192.168.12.103/test1234
access.log:
192.168.12.103 - - [12/sep/2017:02:34:59 -0700] "get /test1234 http/1.0" 200 12 "-" "apachebench/2.3" "-" 127.0.0.1:9095 0.002 0.002 miss
192.168.12.103 - - [12/sep/2017:02:34:59 -0700] "get /test1234 http/1.0" 200 12 "-" "apachebench/2.3" "-" - - 0.502 hit

i know buffers temp file , copies cache. 500ms looks large. knows why?
appreciated.

setup info:

  1. test upstream server
  2. cache located in tmpfs (mount -t tmpfs -o size=512m tmpfs /tmpfs)
  3. nginx version: 1.7.2.1

nginx config

worker_processes  1; error_log  logs/error.log; daemon off; pid        /var/run/nginx.pid; events {} http {     proxy_cache_path /tmpfs/local_cache keys_zone=local_cache:250m levels=1:2 inactive=8s max_size=1g;     proxy_temp_path /tmpfs;     log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '                       '$status $body_bytes_sent "$http_referer" '                       '"$http_user_agent" "$http_x_forwarded_for" '                       '$upstream_addr $upstream_response_time $request_time $upstream_cache_status';      access_log  logs/access.log  main;     server {         listen       80;         server_name  localhost;          location / {                 proxy_pass http://127.0.0.1:9095;                 proxy_cache local_cache;                 proxy_cache_valid 200 2s;                 proxy_cache_lock on;         }      } }

this seems default behaviour. cache locked requests locked worst case 500ms or time_out value.(source)

if upstream response times stable, cache_lock_timeout value little above response time, avoid behaviour. in particular case can set 5ms , first request return in 0-1 ms , locked requests return within 5-6ms.


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