From f6f1628b15e135c7d4f0c5dff1c193c7b16f9a92 Mon Sep 17 00:00:00 2001
From: Marty Schoch <marty.schoch@gmail.com>
Date: Thu, 10 Sep 2015 08:19:05 -0400
Subject: [PATCH] avoid doing unnecessary work:

benchmark            old ns/op     new ns/op     delta
BenchmarkBatch-4     20738739      17047158      -17.80%

benchmark            old allocs     new allocs     delta
BenchmarkBatch-4     136423         136160         -0.19%

benchmark            old bytes     new bytes     delta
BenchmarkBatch-4     20277781      7168772       -64.65%
---
 index/firestorm/comp.go | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/index/firestorm/comp.go b/index/firestorm/comp.go
index b6e920a3..bd0bfb01 100644
--- a/index/firestorm/comp.go
+++ b/index/firestorm/comp.go
@@ -100,12 +100,14 @@ func (c *Compensator) Migrate(docID []byte, docNum uint64, oldDocNums []uint64)
 	defer c.deletedMutex.Unlock()
 
 	// clone deleted doc numbers and mutate
-	newDeletedDocNumbers := c.deletedDocNumbers.Clone()
-	for _, oldDocNum := range oldDocNums {
-		newDeletedDocNumbers.Set(uint(oldDocNum))
+	if len(oldDocNums) > 0 {
+		newDeletedDocNumbers := c.deletedDocNumbers.Clone()
+		for _, oldDocNum := range oldDocNums {
+			newDeletedDocNumbers.Set(uint(oldDocNum))
+		}
+		// update pointer
+		c.deletedDocNumbers = newDeletedDocNumbers
 	}
-	// update pointer
-	c.deletedDocNumbers = newDeletedDocNumbers
 
 	// remove entry from in-flight if it still has same doc num
 	val := c.inFlight.Get(&InFlightItem{docID: docID})