Log Format with $request_body Not working

[aa2funworld]

I am trying to log the incomming HTTP Request with the below given
log_fromat.  It is logging only '-'.  could you please help what I am doing
wrong.

Thanks in advance.

nginx.conf
----------------
http {
include       mime.types;
    default_type  application/octet-stream;
log_format postdata $request_body;
    types_hash_bucket_size 64;
    server_names_hash_bucket_size 128;

 server {
                        listen   9080;
                        server_name X1n2d23;
			
			location / {
			      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
			        proxy_set_header X-Real-IP $remote_addr;
			        proxy_set_header Host $http_host;
			        proxy_redirect off;
			        proxy_pass http://www.google.com;
    				access_log  /nginx/install/log/nginx/log_server.log postdata ;
			    }
}
}

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,257326,257326#msg-257326