[[PageOutline]]
= In cache "Hard Linking" =
== The problem ==
Many of you run your own server/vps that install only 1 copy of each web applications under your server document root, while some other of you, the vhost provider, allow every user install their own copy. For example, [http://www.vbulletin.com/ vBulletin] may be installed under each user's vhost document root. This result in not only disk read/seek without XCache installed, but also consume huge memory for caching them with XCache installed. Most *.php file is bigger after compiled/cached.

== The Solution ==
XCache has introduced a way to solve this headache once and for all. This is called in cache hard linking. Whatever it called, let's see what it does.

It's easier to demonstrate in PHP pseudo code.

{{{
#!php
<?php
function file_entry($filename) {
  if (hash_on_inode()) {
    $stat = stat($filename);
    $hash = hash($stat['inode']);
  }
  else {
    $hash = hash($filename);
  }

  if (!isset($cache[$hash])) {
    $md5 = md5sum($filename);
    if (!isset($phpcache[$md5])) {
      $phpcache[$md5] = php_compile_file($compile);
    }
    $cache[$hash] = &$phpcache[$md5]; // reference, important
  }
  return $cache[$hash];
}

restore_cached_php(find_cached_php($filename));
?>
}}}

== FAQ ==
 * How about the !__FILE!__ and !__DIR!__ in *.php that [ticket:117 get cached]? Don't worry, i had a [changeset:662 back-patching] to fix it already.
 * "I have hard link in filesystem, is !__FILE!__ ok?". Yes, since XCache 2.0.1