Only save dirty fields on Queue queries.

data/database.py

@@ -758,6 +758,11 @@ class QueueItem(BaseModel):
   processing_expires = DateTimeField(null=True, index=True)
   retries_remaining = IntegerField(default=5, index=True)
 
+  class Meta:
+    database = db
+    read_slaves = (read_slave,)
+    only_save_dirty = True
+
 
 class RepositoryBuild(BaseModel):
   uuid = CharField(default=uuid_generator, index=True)

data/queue.py

@@ -270,7 +270,7 @@ class WorkQueue(object):
           queue_item.processing_expires = new_expiration
           has_change = True
 
-        if updated_data is not None:
+        if updated_data is not None and queue_item.body != updated_data:
           queue_item.body = updated_data
           has_change = True