Optimize blob lookup

Fixes #1013

data/model/storage.py

@@ -131,6 +131,15 @@ def _get_storage(query_modifier):
   return found
 
 
+def get_storage_by_subquery(subquery):
+  """ Returns the storage (and its locations) for the storage id returned by the subquery. The
+      subquery must return at most 1 result, which is a storage ID. """
+  def filter_by_subquery(query):
+    return query.where(ImageStorage.id == subquery)
+
+  return _get_storage(filter_by_subquery)
+
+
 def get_storage_by_uuid(storage_uuid):
   def filter_to_uuid(query):
     return query.where(ImageStorage.uuid == storage_uuid)
@@ -202,7 +211,7 @@ def get_storage_locations(uuid):
            .select()
            .join(ImageStorageLocation)
            .switch(ImageStoragePlacement)
-           .join(ImageStorage, JOIN_LEFT_OUTER)
+           .join(ImageStorage)
            .where(ImageStorage.uuid == uuid))
 
   return [location.location.name for location in query]