$http_accept_encoding gets the value of the HTTP Accept-Encoding header.
This might vary depending on the client being used, unless you control them
and their value.
Thus, the same request being made with a different (set of) value(s) in
this header will generate another key.
If you simply want
nginx parses configuration as a whole, either on start or on HUP signal.
Your map is part of the configuration (separating it in multiple files does
not change the fast everything is being merged before being statically
interpreted/compiled), thus you need to signal the master process whenever
