php - Performance of $_SERVER['DOCUMENT_ROOT'], or define("SITE

i need store document root used across application

i have 2 options, please mind explaining quicker , why? or indeed if there better way achieve this.

define("site_root", "/"]);  $_server['document_root']."/path/to/file"

so include created as;

require(site_root.'/path/to/file'); require($_server['document_root']."/path/to/file");

to use:

define("site_root", "/");  //typo removed

is little little bit faster than:

$_server['document_root'] . "/path/to/file"

since concatenate something, constant bit faster. think falls under micro management , don't think biggest performance issue in code.

even if "biggest performance issue", difference small can decide, want use , think more readable.

JVParth