Metadata -> Layout renaming

Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>

tsdb/chunkenc/histogram.go

@@ -64,18 +64,18 @@ func (c *HistogramChunk) NumSamples() int {
 	return int(binary.BigEndian.Uint16(c.Bytes()))
 }
 
-// Meta returns the histogram metadata. Only call this on chunks that have at
+// Layout returns the histogram layout. Only call this on chunks that have at
 // least one sample.
-func (c *HistogramChunk) Meta() (
+func (c *HistogramChunk) Layout() (
 	schema int32, zeroThreshold float64,
 	negativeSpans, positiveSpans []histogram.Span,
 	err error,
 ) {
 	if c.NumSamples() == 0 {
-		panic("HistoChunk.Meta() called on an empty chunk")
+		panic("HistoChunk.Layout() called on an empty chunk")
 	}
 	b := newBReader(c.Bytes()[2:])
-	return readHistogramChunkMeta(&b)
+	return readHistogramChunkLayout(&b)
 }
 
 // CounterResetHeader defines the first 2 bits of the chunk header.
@@ -176,9 +176,9 @@ func newHistogramIterator(b []byte) *histogramIterator {
 		numTotal: binary.BigEndian.Uint16(b),
 		t:        math.MinInt64,
 	}
-	// The first 2 bytes contain chunk headers.
+	// The first 3 bytes contain chunk headers.
 	// We skip that for actual samples.
-	_, _ = it.br.readBits(16)
+	_, _ = it.br.readBits(24)
 	return it
 }
 
@@ -203,7 +203,7 @@ func (c *HistogramChunk) Iterator(it Iterator) Iterator {
 type HistogramAppender struct {
 	b *bstream
 
-	// Metadata:
+	// Layout:
 	schema         int32
 	zThreshold     float64
 	pSpans, nSpans []histogram.Span
@@ -394,15 +394,15 @@ func (a *HistogramAppender) AppendHistogram(t int64, h histogram.Histogram) {
 
 	if value.IsStaleNaN(h.Sum) {
 		// Emptying out other fields to write no buckets, and an empty
-		// meta in case of first histogram in the chunk.
+		// layout in case of first histogram in the chunk.
 		h = histogram.Histogram{Sum: h.Sum}
 	}
 
 	switch num {
 	case 0:
-		// The first append gets the privilege to dictate the metadata
+		// The first append gets the privilege to dictate the layout
 		// but it's also responsible for encoding it into the chunk!
-		writeHistogramChunkMeta(a.b, h.Schema, h.ZeroThreshold, h.PositiveSpans, h.NegativeSpans)
+		writeHistogramChunkLayout(a.b, h.Schema, h.ZeroThreshold, h.PositiveSpans, h.NegativeSpans)
 		a.schema = h.Schema
 		a.zThreshold = h.ZeroThreshold
 
@@ -591,7 +591,7 @@ type histogramIterator struct {
 	numTotal uint16
 	numRead  uint16
 
-	// Metadata:
+	// Layout:
 	schema         int32
 	zThreshold     float64
 	pSpans, nSpans []histogram.Span
@@ -687,11 +687,10 @@ func (it *histogramIterator) Next() bool {
 	}
 
 	if it.numRead == 0 {
-
+		// The first read is responsible for reading the chunk layout
-		// The first read is responsible for reading the chunk metadata
 		// and for initializing fields that depend on it. We give
 		// counter reset info at chunk level, hence we discard it here.
-		schema, zeroThreshold, posSpans, negSpans, err := readHistogramChunkMeta(&it.br)
+		schema, zeroThreshold, posSpans, negSpans, err := readHistogramChunkLayout(&it.br)
 		if err != nil {
 			it.err = err
 			return false

tsdb/chunkenc/histogram_meta.go

@@ -17,14 +17,14 @@ import (
 	"github.com/prometheus/prometheus/model/histogram"
 )
 
-func writeHistogramChunkMeta(b *bstream, schema int32, zeroThreshold float64, positiveSpans, negativeSpans []histogram.Span) {
+func writeHistogramChunkLayout(b *bstream, schema int32, zeroThreshold float64, positiveSpans, negativeSpans []histogram.Span) {
 	putVarbitInt(b, int64(schema))
 	putVarbitFloat(b, zeroThreshold)
-	putHistogramChunkMetaSpans(b, positiveSpans)
+	putHistogramChunkLayoutSpans(b, positiveSpans)
-	putHistogramChunkMetaSpans(b, negativeSpans)
+	putHistogramChunkLayoutSpans(b, negativeSpans)
 }
 
-func putHistogramChunkMetaSpans(b *bstream, spans []histogram.Span) {
+func putHistogramChunkLayoutSpans(b *bstream, spans []histogram.Span) {
 	putVarbitInt(b, int64(len(spans)))
 	for _, s := range spans {
 		putVarbitInt(b, int64(s.Length))
@@ -32,16 +32,11 @@ func putHistogramChunkMetaSpans(b *bstream, spans []histogram.Span) {
 	}
 }
 
-func readHistogramChunkMeta(b *bstreamReader) (
+func readHistogramChunkLayout(b *bstreamReader) (
 	schema int32, zeroThreshold float64,
 	positiveSpans, negativeSpans []histogram.Span,
 	err error,
 ) {
-	_, err = b.ReadByte() // The header.
-	if err != nil {
-		return
-	}
-
 	v, err := readVarbitInt(b)
 	if err != nil {
 		return
@@ -53,12 +48,12 @@ func readHistogramChunkMeta(b *bstreamReader) (
 		return
 	}
 
-	positiveSpans, err = readHistogramChunkMetaSpans(b)
+	positiveSpans, err = readHistogramChunkLayoutSpans(b)
 	if err != nil {
 		return
 	}
 
-	negativeSpans, err = readHistogramChunkMetaSpans(b)
+	negativeSpans, err = readHistogramChunkLayoutSpans(b)
 	if err != nil {
 		return
 	}
@@ -66,7 +61,7 @@ func readHistogramChunkMeta(b *bstreamReader) (
 	return
 }
 
-func readHistogramChunkMetaSpans(b *bstreamReader) ([]histogram.Span, error) {
+func readHistogramChunkLayoutSpans(b *bstreamReader) ([]histogram.Span, error) {
 	var spans []histogram.Span
 	num, err := readVarbitInt(b)
 	if err != nil {