slice module got error when contents of upstream was updated

[t.nishiyori]

Hi Roman,

The slice module is awesome for caching my large content effectively.
But my contents are updated in any times.
I decide to implement some external tools for this error to hear your
answer.
Such like a monitoring error logs and purge unnecessary cache.

Thank you.

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,273307,273412#msg-273412