From dbc88cf6b3990a905ced2641d3f7e60fb7ea25d3 Mon Sep 17 00:00:00 2001
From: Steve Yen <steve.yen@gmail.com>
Date: Tue, 19 Dec 2017 19:15:19 -0800
Subject: [PATCH] scorch docNumberToBytes() checks cap(buf) before allocating

With more pprof focusing (zooming in on a particular func), there were
still some memory allocations showing up with docNumberToBytes() in
micro benchmarks of bleve-query.  On a dev macbook, on an index of 50K
wikipedia docs, using search of relatively common "text:date"...

   400 qps - upsidedown/moss
   680 qps - scorch before
   775 qps - scorch after
---
 index/scorch/snapshot_index.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/index/scorch/snapshot_index.go b/index/scorch/snapshot_index.go
index 7f5f4103..bb6a8be6 100644
--- a/index/scorch/snapshot_index.go
+++ b/index/scorch/snapshot_index.go
@@ -367,7 +367,11 @@ func (i *IndexSnapshot) TermFieldReader(term []byte, field string, includeFreq,
 
 func docNumberToBytes(buf []byte, in uint64) []byte {
 	if len(buf) != 8 {
-		buf = make([]byte, 8)
+		if cap(buf) >= 8 {
+			buf = buf[0:8]
+		} else {
+			buf = make([]byte, 8)
+		}
 	}
 	binary.BigEndian.PutUint64(buf, in)
 	return buf