improve speed of metadata

 * don't load every possible answer, only do what is needed
 * cache instance data for a given address for a 15 seconds
   using either memcache or fake memcache (in-memory).
   This means only a single queue/db lookup for multiple calls
   to metadata service
 * add cache expirey to fake memcache (don't grow forever)
   and move it to nova.common.memorycache

Addresses Bug #851159

Change-Id: Icf794156e055b18915b8b5be9ba2ab97d2338bbe

1 files changed, 64 insertions, 0 deletions

diff --git a/nova/common/memorycache.py b/nova/common/memorycache.py
new file mode 100644
index 000000000..f6a61a1c3
--- /dev/null
+++ b/nova/common/memorycache.py
@@ -0,0 +1,64 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2010 United States Government as represented by the
+# Administrator of the National Aeronautics and Space Administration.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+"""Super simple fake memcache client."""
+
+from nova import utils
+
+
+class Client(object):
+    """Replicates a tiny subset of memcached client interface."""
+
+    def __init__(self, *args, **kwargs):
+        """Ignores the passed in args."""
+        self.cache = {}
+
+    def get(self, key):
+        """Retrieves the value for a key or None.
+
+        this expunges expired keys during each get"""
+
+        for k in self.cache.keys():
+            (timeout, _value) = self.cache[k]
+            if timeout and utils.utcnow_ts() >= timeout:
+                del self.cache[k]
+
+        return self.cache.get(key, (0, None))[1]
+
+    def set(self, key, value, time=0, min_compress_len=0):
+        """Sets the value for a key."""
+        timeout = 0
+        if time != 0:
+            timeout = utils.utcnow_ts() + time
+        self.cache[key] = (timeout, value)
+        return True
+
+    def add(self, key, value, time=0, min_compress_len=0):
+        """Sets the value for a key if it doesn't exist."""
+        if not self.get(key) is None:
+            return False
+        return self.set(key, value, time, min_compress_len)
+
+    def incr(self, key, delta=1):
+        """Increments the value for a key."""
+        value = self.get(key)
+        if value is None:
+            return None
+        new_value = int(value) + delta
+        self.cache[key] = (self.cache[key][0], str(new_value))
+        return new_value