Make Chunks return the number of samples inside

Signed-off-by: Goutham Veeramachaneni <cs14btech11014@iith.ac.in>

chunks/chunk.go

@@ -43,6 +43,7 @@ type Chunk interface {
 	Encoding() Encoding
 	Appender() (Appender, error)
 	Iterator() Iterator
+	NumSamples() int
 }
 
 // FromData returns a chunk from a byte slice of chunk data.

chunks/xor.go

@@ -72,6 +72,11 @@ func (c *XORChunk) Bytes() []byte {
 	return c.b.bytes()
 }
 
+// NumSamples returns the number of samples in the chunk.
+func (c *XORChunk) NumSamples() int {
+	return int(binary.BigEndian.Uint16(c.Bytes()))
+}
+
 // Appender implements the Chunk interface.
 func (c *XORChunk) Appender() (Appender, error) {
 	it := c.iterator()

compact.go

@@ -14,7 +14,6 @@
 package tsdb
 
 import (
-	"encoding/binary"
 	"fmt"
 	"math/rand"
 	"os"
@@ -461,7 +460,7 @@ func populateBlock(blocks []Block, indexw IndexWriter, chunkw ChunkWriter) (*Blo
 		meta.Stats.NumChunks += uint64(len(chks))
 		meta.Stats.NumSeries++
 		for _, chk := range chks {
-			meta.Stats.NumSamples += uint64(binary.BigEndian.Uint16(chk.Chunk.Bytes()))
+			meta.Stats.NumSamples += uint64(chk.Chunk.NumSamples())
 		}
 
 		for _, l := range lset {