cache file has too long header (bug) ?

[Maxim Dounin]

Hello!

On Thu, Sep 10, 2015 at 01:30:46PM -0400, biazus wrote:

> Hey Guys,
> 
> I've been using nginx 1.8.0 for a couple of months, and I noticed a critical
> message at error log informing that "cache file has too long header". 
> 
> 2015/09/10 17:11:03 [crit] 27245#0: *10686 cache file
> "/data/smallfiles/http/6/d8/f5df8d6eda60819319688d1bc0cb2d86" has too long
> header
> 
> However, as you can see at the example bellow, there is nothing abnormal
> with the file:
> 
> cat /data/smallfiles/http/6/d8/f5df8d6eda60819319688d1bc0cb2d86

[...]

The message is logged when nginx detects the problem, ignores the 
cached file and starts loading another response from an upstream 
server.  So, unfortunately, as long as the message appeared, it's 
probably too late to look into the file as it's likely already 
reloaded from a backend.

The message itself is expected to appear if a response header 
stored in the cache file is too big for configured 
proxy_buffer_size.  It may also appear due to a small race 
condition in nginx cache logic if two different responses are 
loaded into cache simultaneously, see here:

http://hg.nginx.org/nginx/rev/6f97afc238de
http://mailman.nginx.org/pipermail/nginx-devel/2011-September/001287.html

The message may also indicates that the cache file was corrupted 
somehow.

If you see the message on a regular basis, we may want to 
investigate further.  If it's just a single case in couple of 
months, it is probably due to the race condition in question and 
likely can be ignored safely.

-- 
Maxim Dounin
http://nginx.org/