[MapProxy] fast 0 byte responses in stead of tiles

[Steven Ottens]

Hi,

I've been asked to investigate why a MapProxy setup sometimes fails to 
deliver tiles. It is mapproxy 1.9 on a VMware server with windows server 
2012 and network attached storage. It is (obviously) not my setup, nor 
well documented :( but what I can see it is running as a windows service 
using cherrypy and python2.7

All the layers are mbtile-caches looking at Geoserver WMS (which runs 
fine) and they are usually fast and I don't see any heavy server load, 
nor is it running out of memory.

However every now and then mapproxy stops delivering the actual tiles, 
but instead delivers within ~20ms an empty tile of 0 bytes. The logs 
seem to be fine, but I'm not entirely sure where I should be looking. 
Once I restart mapproxy all is fine again.

So the question is what might cause mapproxy to deliver empty tiles for 
valid requests, in stead of error messages/log messages?

Cheers,

Steven

BTW. I understand upgrading to a newer version should be a first step, 
but apart from the fact that I don't know (yet) how to upgrade a windows 
service, I don't like to blindly upgrade the software without 
understanding the root cause of the problem