stalled cache updating - what does it mean?

[Richard Stanway]

Hello,
I have a pretty basic PHP / fastcgi setup with a fastcgi cache as follows:

fastcgi_cache_key "$scheme$request_method$host$request_uri";
fastcgi_cache_lock on;
fastcgi_cache_bypass $skip_cache;
fastcgi_no_cache $skip_cache;
fastcgi_cache MAINCACHE;
fastcgi_cache_valid 5m;

I'm using nginx from the nginx.org Debian repository and building from
source, adding the geoip and ngx_cache_purge modules.

nginx version: nginx/1.5.7
built by gcc 4.7.2 (Debian 4.7.2-5)
TLS SNI support enabled

Every so often I'll get a couple of lines in the log like the following:

2013/12/09 15:59:34 [alert] 14218#0: *10450047 stalled cache updating,
error:0 while closing request, client: x.236.101.34, server: x.x.101.37:80
2013/12/09 15:59:34 [alert] 14218#0: *10450055 stalled cache updating,
error:0 while closing request, client: x.236.101.34, server: x.x.101.37:80
2013/12/09 15:59:34 [alert] 14218#0: *10450099 stalled cache updating,
error:0 while closing request, client: x.236.101.34, server: x.x.101.37:80

This usually occurs after a client requests a script which issues some
internal requests to the site itself (wp-cron).

As it's log level alert, it seems serious, but I can't seem to notice
anything wrong as a result. What exactly does this alert mean and is it
something I need to be worried about? I've since moved the script to an
offline cron job to see if this helps, but I'm still curious exactly what
this means.

Thanks,

Rich.
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