New patch against hostvars.py. With this patch, Ansible run lose 50% of time.

Little rewrite of previous patch to use sha1 signature.
Use fail_on_undefined to compute sha1 signature.

lib/ansible/vars/hostvars.py

@@ -28,6 +28,11 @@ from ansible import constants as C
 from ansible.inventory.host import Host
 from ansible.template import Templar
 
+try:
+    from hashlib import sha1
+except ImportError:
+    from sha import sha as sha1
+
 __all__ = ['HostVars']
 
 # Note -- this is a Mapping, not a MutableMapping
@@ -39,6 +44,7 @@ class HostVars(collections.Mapping):
         self._loader = loader
         self._play = play
         self._variable_manager = variable_manager
+        self._cached_result = {}
 
         hosts = inventory.get_hosts(ignore_limits_and_restrictions=True)
 
@@ -68,8 +74,16 @@ class HostVars(collections.Mapping):
 
         host = self._lookup.get(host_name)
         data = self._variable_manager.get_vars(loader=self._loader, host=host, play=self._play, include_hostvars=False)
-        templar = Templar(variables=data, loader=self._loader)
-        return templar.template(data, fail_on_undefined=False)
+
+        # Using cache in order to avoid template call
+        sha1_hash = sha1(str(data)).hexdigest()
+        if sha1_hash in self._cached_result:
+            result = self._cached_result[sha1_hash]
+        else:
+            templar = Templar(variables=data, loader=self._loader)
+            result = templar.template(data, fail_on_undefined=False)
+            self._cached_result[sha1_hash] = result
+        return result
 
     def __contains__(self, host_name):
         item = self.get(host_name)