Use shared memory caching facilities

[dammit]

Index: wp-includes/cache.php
===================================================================
--- wp-includes/cache.php       (revision 3809)
+++ wp-includes/cache.php       (working copy)
@@ -31,8 +31,13 @@
 
 function wp_cache_init() {
        global $wp_object_cache;
-
-       $wp_object_cache = new WP_Object_Cache();
+       if (defined('DISABLE_CACHE') or !defined('ENABLE_CACHE')) {
+               $wp_object_cache = new WP_Object_Cache_Void();
+       } elseif (function_exists('apc_store')) {
+               $wp_object_cache = new WP_Object_Cache_APC();
+       } else {
+               $wp_object_cache = new WP_Object_Cache();
+       }
 }
 
 function wp_cache_replace($key, $data, $flag = '', $expire = 0) {
@@ -417,4 +422,56 @@
                $this->blog_id = md5($blog_id);
        }
 }
+
+/**
+ * Base class for shared-memory enabled caches, like APC, Turck, etc
+ */
+class WP_Object_Cache_Void {
+       /* May be reused by children */
+       function add($id, $data, $group='default', $expire=0) { 
+               if (empty($group))
+                       $group = 'default';
+               if ($this->get($id, $group))
+                       return false;
+               return $this->set($id, $data, $group, $expire);
+       }
+       /* May be reused */
+       function replace($id, $data, $group = 'default', $expire = 0) {
+               if (empty ($group))
+                       $group = 'default';
+
+               if (false === $this->get($id, $group))
+                       return false;
+
+               return $this->set($id, $data, $group, $expire);
+       }
+
+       /* Just a common useful function :) */
+       function getKey($id,$group) {
+               global $blog_id;
+               return "{$blog_id}:{$id}:{$group}";
+       }
+
+       function save() { return true; }
+       function delete($id, $group = 'default', $force = false) { return true; }
+       function flush() { return true; }
+       function get($id, $group = 'default') { return false; }
+       function set($id, $data, $group = 'default', $expire = 0) { return true;}
+}
+
+class WP_Object_Cache_APC extends WP_Object_Cache_Void {
+       function get($id,$group='default') {
+               if (empty ($group)) $group = 'default';
+               return apc_fetch($this->getKey($id,$group));
+       }
+       function set($id,$data,$group='default',$expire=0) {
+               if (empty ($group)) $group = 'default';
+               return apc_store($this->getkey($id,$group),$data,$expire);
+       }
+       function delete($id,$group='default', $forse = false) {
+               if (empty ($group)) $group = 'default';
+               return apc_delete($this->getkey($id,$group));
+       }
+}
+
 ?>

For APC, you'll need to put ABSPATH into the key, or multiple blogs on the same server will interfere with each other. Also, I've had problems with APC (using my own object cache backend) returning the wrong category (e.g. :category:1 will return data from :category:112 sometimes). I'm still investigating it... my solution for now has been to md5 the key, to ensure that I don't get some sort of partial match.

right, adding md5sum( ABSPATH . dbname . blogid) would be probably a good way to go.

there is something yet not complete here, as it failed to work on my main blog, I'll try testing in 'lab'.

No traction in over a year, so closing as wontfix.

Feel free to reopen if you have patches/suggestions/...