Fix XenAPI performance issue

This patch implements 'list_instance_uuids' in the xenapi virt driver so
that compute manager's '_get_instances_on_driver' can operate more
efficiently.

Fixes bug 1097980

The cleanup_running_deleted_instances periodic task uses the above call
while context has been modified to be read_deleted='yes'.  Without
list_instance_uuids being implemented in xenapi, there's a fallback to
querying all instances on the host.  Because of read_deleted='yes', this
queries all instances that have ever lived on the host.  In a very busy
environment where instances are repeatedly built and destroyed, one can
end up with thousands of deleted instances.  Now that we are storing
instance_type data in system_metadata and system_metadata is joined with
every instance_get, this results in 10x the number of rows being
returned with sqlalchemy... the fallback doesn't perform well enough.

Change-Id: I4bbfd69c9769807cec813af757665f03d9643460

nova/tests/test_xenapi.py

@@ -374,6 +374,19 @@ def test_list_instances_0(self):
         instances = self.conn.list_instances()
         self.assertEquals(instances, [])
 
+    def test_list_instance_uuids_0(self):
+        instance_uuids = self.conn.list_instance_uuids()
+        self.assertEquals(instance_uuids, [])
+
+    def test_list_instance_uuids(self):
+        uuids = []
+        for x in xrange(1, 4):
+            instance = self._create_instance(x)
+            uuids.append(instance['uuid'])
+        instance_uuids = self.conn.list_instance_uuids()
+        self.assertEqual(len(uuids), len(instance_uuids))
+        self.assertEqual(set(uuids), set(instance_uuids))
+
     def test_get_rrd_server(self):
         self.flags(xenapi_connection_url='myscheme://myaddress/')
         server_info = vm_utils._get_rrd_server()

nova/virt/xenapi/driver.py

@@ -164,6 +164,12 @@ def list_instances(self):
         """List VM instances."""
         return self._vmops.list_instances()
 
+    def list_instance_uuids(self):
+        """Get the list of nova instance uuids for VMs found on the
+        hypervisor.
+        """
+        return self._vmops.list_instance_uuids()
+
     def spawn(self, context, instance, image_meta, injected_files,
               admin_password, network_info=None, block_device_info=None):
         """Create VM instance."""

nova/virt/xenapi/vmops.py

@@ -190,6 +190,18 @@ def list_instances(self):
 
         return name_labels
 
+    def list_instance_uuids(self):
+        """Get the list of nova instance uuids for VMs found on the
+        hypervisor.
+        """
+        nova_uuids = []
+        for vm_ref, vm_rec in vm_utils.list_vms(self._session):
+            other_config = vm_rec['other_config']
+            nova_uuid = other_config.get('nova_uuid')
+            if nova_uuid:
+                nova_uuids.append(nova_uuid)
+        return nova_uuids
+
     def confirm_migration(self, migration, instance, network_info):
         name_label = self._get_orig_vm_name_label(instance)
         vm_ref = vm_utils.lookup(self._session, name_label)