Switch disk_config extension to use one DB query

A response through this extension can have many servers and making one
query per server can slow down response time dramatically. This change
switches the extension to use one DB query instead of many queries.
It also avoids queries when the key is already populated, such as when
the results include responses from a remote zone.

This change reduces a 'nova list' of 21 servers from 14 seconds to 1
second on my (relatively slow) development system.

Change-Id: I8476dbca0f87ff2a3d69bd7b8f51c296e41e3388

1 files changed, 14 insertions, 3 deletions

diff --git a/nova/api/openstack/v2/contrib/disk_config.py b/nova/api/openstack/v2/contrib/disk_config.py
index 6e26c1daa..7ce24a3fd 100644
--- a/nova/api/openstack/v2/contrib/disk_config.py
+++ b/nova/api/openstack/v2/contrib/disk_config.py
@@ -23,6 +23,7 @@ from webob import exc
 from nova.api.openstack.v2 import extensions
 from nova.api.openstack import xmlutil
 from nova import compute
+from nova import db
 from nova import log as logging
 from nova import utils
 
@@ -118,10 +119,20 @@ class Disk_config(extensions.ExtensionDescriptor):
             singular='server', singular_template=ServerDiskConfigTemplate(),
             plural='servers', plural_template=ServersDiskConfigTemplate())
 
+        # Filter out any servers that already have the key set (most likely
+        # from a remote zone)
+        servers = filter(lambda s: self.API_DISK_CONFIG not in s, servers)
+
+        # Get DB information for servers
+        uuids = [server['id'] for server in servers]
+        db_servers = db.instance_get_all_by_filters(context, {'uuid': uuids})
+        db_servers = dict([(s['uuid'], s) for s in db_servers])
+
         for server in servers:
-            db_server = self.compute_api.routing_get(context, server['id'])
-            value = db_server[self.INTERNAL_DISK_CONFIG]
-            server[self.API_DISK_CONFIG] = disk_config_to_api(value)
+            db_server = db_servers.get(server['id'])
+            if db_server:
+                value = db_server[self.INTERNAL_DISK_CONFIG]
+                server[self.API_DISK_CONFIG] = disk_config_to_api(value)
 
         return res