fastcgi_cache_lock doesnt work

[permyakovsv]

I have further configuration:
                fastcgi_cache fastcgi_cache_products;
                fastcgi_cache_valid 200 302 304 404 25m;
                fastcgi_cache_valid 301 5m;
                fastcgi_cache_valid 500 502 20s;

                fastcgi_cache_lock on;
                fastcgi_cache_lock_timeout 25s;
                fastcgi_cache_use_stale updating error timeout
invalid_header http_500 http_503;

And I see netx picture:
date 	                             http_code http_cache_status
backend_responce
...
17/Nov/2016:17:19:54 +0200      200     cs=HIT  0
17/Nov/2016:17:19:14 +0200      200     cs=EXPIRED      8.041
17/Nov/2016:17:18:07 +0200      200     cs=EXPIRED      3.218
17/Nov/2016:17:17:24 +0200      200     cs=EXPIRED      3.291
17/Nov/2016:17:17:21 +0200      200     cs=UPDATING     0
17/Nov/2016:17:16:14 +0200      200     cs=EXPIRED      3.538
17/Nov/2016:17:15:53 +0200      200     cs=EXPIRED      2.977
17/Nov/2016:17:14:32 +0200      200     cs=EXPIRED      4.119
17/Nov/2016:17:13:49 +0200      200     cs=EXPIRED      4.784
17/Nov/2016:17:13:04 +0200      200     cs=HIT  0
...
17/Nov/2016:16:48:44 +0200      200     cs=HIT  0
17/Nov/2016:16:48:37 +0200      200     cs=EXPIRED      4.279
17/Nov/2016:16:47:57 +0200      200     cs=EXPIRED      3.936
17/Nov/2016:16:47:46 +0200      200     cs=EXPIRED      3.447
17/Nov/2016:16:46:53 +0200      200     cs=EXPIRED      3.287
...

But I expect only one request to backend, and why first request didn't
update cache?
Maybe Anybody faced the same problem?

Posted at Nginx Forum: https://forum.nginx.org/read.php?21,271014,271014#msg-271014