why will nginx's map directive eat all ram?

[Payne Chu]

recently I try to use map directive to make my nginx.conf DRY. like below

`map $pid $public_root { default public; }`

and in one of server directive I put below

`root $public_root;`

I try to `ab` test with retrieve a static html. the nginx will eat all ram.
if I reset back to `root public;` it will maintain the ram in low evel.

so we should avoid to use map directive ? 

My Env: MACOSX 10.8.4, Nginx 1.4.1

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,241478,241478#msg-241478