From 793acd9a1c6d294bf4076dcb3bccd8bacf72cd42 Mon Sep 17 00:00:00 2001
From: Gav <gavin@parity.io>
Date: Tue, 13 Feb 2018 18:00:21 +0100
Subject: [PATCH] Avoid pointless work

---
 substrate/substrate/state-machine/src/lib.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/substrate/substrate/state-machine/src/lib.rs b/substrate/substrate/state-machine/src/lib.rs
index 07d9683b3d..e6127beb1e 100644
--- a/substrate/substrate/state-machine/src/lib.rs
+++ b/substrate/substrate/state-machine/src/lib.rs
@@ -99,7 +99,11 @@ impl OverlayedChanges {
 
 	/// Commit prospective changes to state.
 	pub fn commit_prospective(&mut self) {
-		self.committed.update(self.prospective.storage.drain());
+		if self.committed.storage.is_empty() {
+			::std::mem::swap(&mut self.prospective, &mut self.committed);
+		} else {
+			self.committed.update(self.prospective.storage.drain());
+		}
 	}
 
 	/// Drain prospective changes to an iterator.