From a8c22c85cc610a4d479dc4c8dcc9f2c9325e95f4 Mon Sep 17 00:00:00 2001
From: Brian Brazil <brian.brazil@robustperception.io>
Date: Mon, 12 Mar 2018 13:16:59 +0000
Subject: [PATCH] Correctly handle pruning wraparound after ring expansion
 (#3942)

Fixes #3939
---
 storage/buffer.go      | 1 +
 storage/buffer_test.go | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/storage/buffer.go b/storage/buffer.go
index 0159cfa3f..77476c614 100644
--- a/storage/buffer.go
+++ b/storage/buffer.go
@@ -178,6 +178,7 @@ func (r *sampleRing) add(t int64, v float64) {
 		r.buf = buf
 		r.i = r.f
 		r.f += l
+		l = 2 * l
 	} else {
 		r.i++
 		if r.i >= l {
diff --git a/storage/buffer_test.go b/storage/buffer_test.go
index 2a1b87248..5b752dec2 100644
--- a/storage/buffer_test.go
+++ b/storage/buffer_test.go
@@ -48,6 +48,11 @@ func TestSampleRing(t *testing.T) {
 			delta: 7,
 			size:  1,
 		},
+		{
+			input: []int64{1, 2, 3, 4, 6},
+			delta: 4,
+			size:  4,
+		},
 	}
 	for _, c := range cases {
 		r := newSampleRing(c.delta, c.size)