How to load nginx config dynamiclly like apache .htaccess?

[JWD]

How to load nginx config dynamiclly like apache .htaccess?
Many people talk about it, but I still can't find a way to make it work.

Anather question:
If I "mv access.log access.log.old", will access record be logged in cache or dropped befor I create a new access.log?
If logged in cache, how many access record can be logged in cache? After cache is full, will access record be dropped?