[users@httpd] mod_cache 103 error "Software caused connection abort"

[Neil Gunton <ne...@nilspace.com>]

Hi, I am using httpd 2.2.17, build from source on Debian Squeeze AMD64 
(quadcore Xeon, 4GB RAM). This server is running a community website 
that gets around 100,000 page requests per day - so, not really all that 
busy. The system always seems to have plenty of resources available.

The site uses a front end caching reverse proxy setup, via two builds of 
httpd. The back end app server is mod_perl + mysql, run on the same box. 
I use mod_rewrite to handle the proxy redirects to internal ports on the 
backend.

I have been seeing some odd errors in the proxy error log, like this:

[Tue May 03 16:17:51 2011] [error] (103)Software caused connection 
abort: cache: error returned while trying to return disk cached data

There are about 160 of those so far today, and there were 388 yesterday.

Doing searches on the error string doesn't seem to bring up much info. 
As far as I can tell, the site is working ok, lots of people using it, 
and I haven't seen anybody making complaints about broken pages. The 
requests that seem to produce the error are not badly formed, they are 
for regular pages. The errors just seem to randomly happen. I don't even 
know what "103" as an error code is supposed to mean - it's not one of 
the commonly used HTTP error codes as far as I can tell.

I run htcacheclean every 10 minutes via cron. My cache is two level, 
with single character directory names, and with the cache cleaning it 
never exceeds about 170MB. The hard drive is not anywhere near full.

Does anybody have any insights on what causes these errors? I saw a 
comment somewhere about MaxClients, but it is set to 250 on the proxy, 
and I don't think it's hitting that limit for me.

Any clues would be much appreciated...

Thanks,

Neil

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