added a memcached option. It's really slow though. don't use it.

overviewer.py

@@ -350,6 +350,8 @@ dir but you forgot to put quotes around the directory, since it contains spaces.
     # Set up the cache objects to use
     caches = []
     caches.append(cache.LRUCache(size=100))
+    if config.get("memcached_host", False):
+        caches.append(cache.Memcached(config['memcached_host']))
     # TODO: optionally more caching layers here
 
     renders = config['renders']

overviewer_core/cache.py

@@ -22,6 +22,7 @@ attribute.
 """
 import functools
 import logging
+import cPickle
 
 class LRUCache(object):
     """A simple, generic, in-memory LRU cache that implements the standard
@@ -124,3 +125,30 @@ class LRUCache(object):
 
         cache[key] = link
 
+# memcached is an option, but unless your IO costs are really high, it just
+# ends up adding overhead and isn't worth it.
+try:
+    import memcache
+except ImportError:
+    class Memcached(object):
+        def __init__(*args):
+            raise ImportError("No module 'memcache' found. Please install python-memcached")
+else:
+    class Memcached(object):
+        def __init__(self, conn='127.0.0.1:11211'):
+            self.conn = conn
+            self.mc = memcache.Client([conn], debug=0, pickler=cPickle.Pickler, unpickler=cPickle.Unpickler)
+
+        def __getstate__(self):
+            return self.conn
+        def __setstate__(self, conn):
+            self.__init__(conn)
+
+        def __getitem__(self, key):
+            v = self.mc.get(key)
+            if not v:
+                raise KeyError()
+            return v
+
+        def __setitem__(self, key, value):
+            self.mc.set(key, value)

overviewer_core/settingsDefinition.py

@@ -86,3 +86,7 @@ worlds = Setting(required=True, validator=make_dictValidator(validateStr, valida
 outputdir = Setting(required=True, validator=validateOutputDir, default=None)
 
 processes = Setting(required=True, validator=int, default=-1)
+
+# memcached is an option, but unless your IO costs are really high, it just
+# ends up adding overhead and isn't worth it.
+memcached_host = Setting(required=False, validator=str, default=None)

overviewer_core/world.py

@@ -18,6 +18,7 @@ import os
 import os.path
 from glob import glob
 import logging
+import hashlib
 
 import numpy
 
@@ -581,14 +582,13 @@ class CachedRegionSet(RegionSetWrapper):
         s += obj.regiondir
 
         logging.debug("Initializing a cache with key '%s'", s)
-        if len(s) > 32:
-            import hashlib
-            s = hashlib.md5(s).hexdigest()
+
+        s = hashlib.md5(s).hexdigest()
 
         self.key = s
 
     def get_chunk(self, x, z):
-        key = (self.key, x, z)
+        key = hashlib.md5(repr((self.key, x, z))).hexdigest()
         for i, cache in enumerate(self.caches):
             try:
                 retval = cache[key]