Why not use Lua, collect the data from your variables, run the query (and optionally store them in a Lua cache) and process it all real-time, none-blocking and without any (extra) module.

Examples:
http://stackoverflow.com/questions/25955869/how-do-i-use-mysql-for-dynamic-doc-root-with-nginx
https://github.com/openresty/lua-resty-mysql

https://github.com/openresty/lua-nginx-module

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nginx for Windows http://nginx-win.ecsds.eu/