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

1 files changed, 13 insertions, 0 deletions

diff --git a/nova/tests/test_xenapi.py b/nova/tests/test_xenapi.py
index 6714161f1..330a229ab 100644
--- a/nova/tests/test_xenapi.py
+++ b/nova/tests/test_xenapi.py
@@ -374,6 +374,19 @@ class XenAPIVMTestCase(stubs.XenAPITestBase):
         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()