From c212ef03265262ecc61c370b27468c4c0af7fcca Mon Sep 17 00:00:00 2001
From: Julius Volz <julius@soundcloud.com>
Date: Wed, 5 Oct 2016 20:32:55 +0200
Subject: [PATCH] Add Chunk.Utilization() methods

When using the chunking code in other projects (both Weave Prism and
ChronixDB ingester), you sometimes want to know how well you are
utilizing your chunks when closing/storing them.
---
 storage/local/chunk/chunk.go       | 1 +
 storage/local/chunk/delta.go       | 5 +++++
 storage/local/chunk/doubledelta.go | 5 +++++
 storage/local/chunk/varbit.go      | 6 ++++++
 4 files changed, 17 insertions(+)

diff --git a/storage/local/chunk/chunk.go b/storage/local/chunk/chunk.go
index d26237394..738e678f1 100644
--- a/storage/local/chunk/chunk.go
+++ b/storage/local/chunk/chunk.go
@@ -273,6 +273,7 @@ type Chunk interface {
 	Unmarshal(io.Reader) error
 	UnmarshalFromBuf([]byte) error
 	Encoding() Encoding
+	Utilization() float64
 }
 
 // Iterator enables efficient access to the content of a chunk. It is
diff --git a/storage/local/chunk/delta.go b/storage/local/chunk/delta.go
index f9bbff4a8..911ab63fa 100644
--- a/storage/local/chunk/delta.go
+++ b/storage/local/chunk/delta.go
@@ -267,6 +267,11 @@ func (c *deltaEncodedChunk) UnmarshalFromBuf(buf []byte) error {
 // encoding implements chunk.
 func (c deltaEncodedChunk) Encoding() Encoding { return Delta }
 
+// Utilization implements chunk.
+func (c deltaEncodedChunk) Utilization() float64 {
+	return float64(len(c)) / float64(cap(c))
+}
+
 func (c deltaEncodedChunk) timeBytes() deltaBytes {
 	return deltaBytes(c[deltaHeaderTimeBytesOffset])
 }
diff --git a/storage/local/chunk/doubledelta.go b/storage/local/chunk/doubledelta.go
index debf5232d..51cc60346 100644
--- a/storage/local/chunk/doubledelta.go
+++ b/storage/local/chunk/doubledelta.go
@@ -277,6 +277,11 @@ func (c *doubleDeltaEncodedChunk) UnmarshalFromBuf(buf []byte) error {
 // encoding implements chunk.
 func (c doubleDeltaEncodedChunk) Encoding() Encoding { return DoubleDelta }
 
+// Utilization implements chunk.
+func (c doubleDeltaEncodedChunk) Utilization() float64 {
+	return float64(len(c)) / float64(cap(c))
+}
+
 func (c doubleDeltaEncodedChunk) baseTime() model.Time {
 	return model.Time(
 		binary.LittleEndian.Uint64(
diff --git a/storage/local/chunk/varbit.go b/storage/local/chunk/varbit.go
index f5590abd3..21f7cd759 100644
--- a/storage/local/chunk/varbit.go
+++ b/storage/local/chunk/varbit.go
@@ -322,6 +322,12 @@ func (c varbitChunk) UnmarshalFromBuf(buf []byte) error {
 // encoding implements chunk.
 func (c varbitChunk) Encoding() Encoding { return Varbit }
 
+// Utilization implements chunk.
+func (c varbitChunk) Utilization() float64 {
+	// 15 bytes is the length of the chunk footer.
+	return math.Min(float64(c.nextSampleOffset()/8+15)/float64(cap(c)), 1)
+}
+
 // FirstTime implements chunk.
 func (c varbitChunk) FirstTime() model.Time {
 	return model.Time(