[REFACTOR] TSDB chunks: replace magic numbers with constants (#17095)

For size of header and position of flags byte.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

tsdb/chunkenc/float_histogram.go

@@ -41,7 +41,7 @@ type FloatHistogramChunk struct {
 
 // NewFloatHistogramChunk returns a new chunk with float histogram encoding.
 func NewFloatHistogramChunk() *FloatHistogramChunk {
-	b := make([]byte, 3, 128)
+	b := make([]byte, histogramHeaderSize, chunkAllocationSize)
 	return &FloatHistogramChunk{b: bstream{stream: b, count: 0}}
 }
 
@@ -75,7 +75,7 @@ func (c *FloatHistogramChunk) NumSamples() int {
 // GetCounterResetHeader returns the info about the first 2 bits of the chunk
 // header.
 func (c *FloatHistogramChunk) GetCounterResetHeader() CounterResetHeader {
-	return CounterResetHeader(c.Bytes()[2] & CounterResetHeaderMask)
+	return CounterResetHeader(c.Bytes()[histogramFlagPos] & CounterResetHeaderMask)
 }
 
 // Compact implements the Chunk interface.
@@ -89,7 +89,7 @@ func (c *FloatHistogramChunk) Compact() {
 
 // Appender implements the Chunk interface.
 func (c *FloatHistogramChunk) Appender() (Appender, error) {
-	if len(c.b.stream) == 3 { // Avoid allocating an Iterator when chunk is empty.
+	if len(c.b.stream) == histogramHeaderSize { // Avoid allocating an Iterator when chunk is empty.
 		return &FloatHistogramAppender{b: &c.b, t: math.MinInt64, sum: xorValue{leading: 0xff}, cnt: xorValue{leading: 0xff}, zCnt: xorValue{leading: 0xff}}, nil
 	}
 	it := c.iterator(nil)
@@ -153,14 +153,11 @@ func (c *FloatHistogramChunk) iterator(it Iterator) *floatHistogramIterator {
 
 func newFloatHistogramIterator(b []byte) *floatHistogramIterator {
 	it := &floatHistogramIterator{
-		br:       newBReader(b),
+		br:       newBReader(b[histogramHeaderSize:]),
 		numTotal: binary.BigEndian.Uint16(b),
 		t:        math.MinInt64,
 	}
-	// The first 3 bytes contain chunk headers.
-	// We skip that for actual samples.
-	_, _ = it.br.readBits(24)
-	it.counterResetHeader = CounterResetHeader(b[2] & CounterResetHeaderMask)
+	it.counterResetHeader = CounterResetHeader(b[histogramFlagPos] & CounterResetHeaderMask)
 	return it
 }
 
@@ -185,11 +182,11 @@ type FloatHistogramAppender struct {
 }
 
 func (a *FloatHistogramAppender) GetCounterResetHeader() CounterResetHeader {
-	return CounterResetHeader(a.b.bytes()[2] & CounterResetHeaderMask)
+	return CounterResetHeader(a.b.bytes()[histogramFlagPos] & CounterResetHeaderMask)
 }
 
 func (a *FloatHistogramAppender) setCounterResetHeader(cr CounterResetHeader) {
-	a.b.bytes()[2] = (a.b.bytes()[2] & (^CounterResetHeaderMask)) | (byte(cr) & CounterResetHeaderMask)
+	a.b.bytes()[histogramFlagPos] = (a.b.bytes()[histogramFlagPos] & (^CounterResetHeaderMask)) | (byte(cr) & CounterResetHeaderMask)
 }
 
 func (a *FloatHistogramAppender) NumSamples() int {
@@ -665,7 +662,7 @@ func (a *FloatHistogramAppender) recode(
 		happ.appendFloatHistogram(tOld, hOld)
 	}
 
-	happ.setCounterResetHeader(CounterResetHeader(byts[2] & CounterResetHeaderMask))
+	happ.setCounterResetHeader(CounterResetHeader(byts[histogramFlagPos] & CounterResetHeaderMask))
 	return hc, app
 }
 
@@ -920,11 +917,11 @@ func (it *floatHistogramIterator) Err() error {
 func (it *floatHistogramIterator) Reset(b []byte) {
 	// The first 3 bytes contain chunk headers.
 	// We skip that for actual samples.
-	it.br = newBReader(b[3:])
+	it.br = newBReader(b[histogramHeaderSize:])
 	it.numTotal = binary.BigEndian.Uint16(b)
 	it.numRead = 0
 
-	it.counterResetHeader = CounterResetHeader(b[2] & CounterResetHeaderMask)
+	it.counterResetHeader = CounterResetHeader(b[histogramFlagPos] & CounterResetHeaderMask)
 
 	it.t, it.tDelta = 0, 0
 	it.cnt, it.zCnt, it.sum = xorValue{}, xorValue{}, xorValue{}

tsdb/chunkenc/histogram.go

@@ -42,7 +42,7 @@ type HistogramChunk struct {
 // NewHistogramChunk returns a new chunk with histogram encoding of the given
 // size.
 func NewHistogramChunk() *HistogramChunk {
-	b := make([]byte, 3, 128)
+	b := make([]byte, histogramHeaderSize, chunkAllocationSize)
 	return &HistogramChunk{b: bstream{stream: b, count: 0}}
 }
 
@@ -78,15 +78,18 @@ const (
 	// UnknownCounterReset means we cannot say if this chunk was created due to a counter reset or not.
 	// An explicit counter reset detection needs to happen during query time.
 	UnknownCounterReset CounterResetHeader = 0b00000000
+	// CounterResetHeaderMask is the mask to get the counter reset header bits.
+	CounterResetHeaderMask byte = 0b11000000
+	// Position within the header bytes at the start of the stream.
+	histogramFlagPos = 2
+	// Total header size.
+	histogramHeaderSize = 3
 )
 
-// CounterResetHeaderMask is the mask to get the counter reset header bits.
-const CounterResetHeaderMask byte = 0b11000000
-
 // GetCounterResetHeader returns the info about the first 2 bits of the chunk
 // header.
 func (c *HistogramChunk) GetCounterResetHeader() CounterResetHeader {
-	return CounterResetHeader(c.Bytes()[2] & CounterResetHeaderMask)
+	return CounterResetHeader(c.Bytes()[histogramFlagPos] & CounterResetHeaderMask)
 }
 
 // Compact implements the Chunk interface.
@@ -100,7 +103,7 @@ func (c *HistogramChunk) Compact() {
 
 // Appender implements the Chunk interface.
 func (c *HistogramChunk) Appender() (Appender, error) {
-	if len(c.b.stream) == 3 { // Avoid allocating an Iterator when chunk is empty.
+	if len(c.b.stream) == histogramHeaderSize { // Avoid allocating an Iterator when chunk is empty.
 		return &HistogramAppender{b: &c.b, t: math.MinInt64, leading: 0xff}, nil
 	}
 	it := c.iterator(nil)
@@ -150,14 +153,11 @@ func countSpans(spans []histogram.Span) int {
 
 func newHistogramIterator(b []byte) *histogramIterator {
 	it := &histogramIterator{
-		br:       newBReader(b),
+		br:       newBReader(b[histogramHeaderSize:]),
 		numTotal: binary.BigEndian.Uint16(b),
 		t:        math.MinInt64,
 	}
-	// The first 3 bytes contain chunk headers.
-	// We skip that for actual samples.
-	_, _ = it.br.readBits(24)
-	it.counterResetHeader = CounterResetHeader(b[2] & CounterResetHeaderMask)
+	it.counterResetHeader = CounterResetHeader(b[histogramFlagPos] & CounterResetHeaderMask)
 	return it
 }
 
@@ -206,11 +206,11 @@ type HistogramAppender struct {
 }
 
 func (a *HistogramAppender) GetCounterResetHeader() CounterResetHeader {
-	return CounterResetHeader(a.b.bytes()[2] & CounterResetHeaderMask)
+	return CounterResetHeader(a.b.bytes()[histogramFlagPos] & CounterResetHeaderMask)
 }
 
 func (a *HistogramAppender) setCounterResetHeader(cr CounterResetHeader) {
-	a.b.bytes()[2] = (a.b.bytes()[2] & (^CounterResetHeaderMask)) | (byte(cr) & CounterResetHeaderMask)
+	a.b.bytes()[histogramFlagPos] = (a.b.bytes()[histogramFlagPos] & (^CounterResetHeaderMask)) | (byte(cr) & CounterResetHeaderMask)
 }
 
 func (a *HistogramAppender) NumSamples() int {
@@ -710,7 +710,7 @@ func (a *HistogramAppender) recode(
 		happ.appendHistogram(tOld, hOld)
 	}
 
-	happ.setCounterResetHeader(CounterResetHeader(byts[2] & CounterResetHeaderMask))
+	happ.setCounterResetHeader(CounterResetHeader(byts[histogramFlagPos] & CounterResetHeaderMask))
 	return hc, app
 }
 
@@ -1026,11 +1026,11 @@ func (it *histogramIterator) Err() error {
 func (it *histogramIterator) Reset(b []byte) {
 	// The first 3 bytes contain chunk headers.
 	// We skip that for actual samples.
-	it.br = newBReader(b[3:])
+	it.br = newBReader(b[histogramHeaderSize:])
 	it.numTotal = binary.BigEndian.Uint16(b)
 	it.numRead = 0
 
-	it.counterResetHeader = CounterResetHeader(b[2] & CounterResetHeaderMask)
+	it.counterResetHeader = CounterResetHeader(b[histogramFlagPos] & CounterResetHeaderMask)
 
 	it.t, it.cnt, it.zCnt = 0, 0, 0
 	it.tDelta, it.cntDelta, it.zCntDelta = 0, 0, 0

tsdb/chunkenc/xor.go

@@ -52,6 +52,8 @@ import (
 )
 
 const (
+	chunkHeaderSize               = 2
+	chunkAllocationSize           = 128
 	chunkCompactCapacityThreshold = 32
 )
 
@@ -62,7 +64,7 @@ type XORChunk struct {
 
 // NewXORChunk returns a new chunk with XOR encoding.
 func NewXORChunk() *XORChunk {
-	b := make([]byte, 2, 128)
+	b := make([]byte, chunkHeaderSize, chunkAllocationSize)
 	return &XORChunk{b: bstream{stream: b, count: 0}}
 }
 
@@ -98,7 +100,7 @@ func (c *XORChunk) Compact() {
 // It is not valid to call Appender() multiple times concurrently or to use multiple
 // Appenders on the same chunk.
 func (c *XORChunk) Appender() (Appender, error) {
-	if len(c.b.stream) == 2 { // Avoid allocating an Iterator when chunk is empty.
+	if len(c.b.stream) == chunkHeaderSize { // Avoid allocating an Iterator when chunk is empty.
 		return &xorAppender{b: &c.b, t: math.MinInt64, leading: 0xff}, nil
 	}
 	it := c.iterator(nil)
@@ -131,7 +133,7 @@ func (c *XORChunk) iterator(it Iterator) *xorIterator {
 	return &xorIterator{
 		// The first 2 bytes contain chunk headers.
 		// We skip that for actual samples.
-		br:       newBReader(c.b.bytes()[2:]),
+		br:       newBReader(c.b.bytes()[chunkHeaderSize:]),
 		numTotal: binary.BigEndian.Uint16(c.b.bytes()),
 		t:        math.MinInt64,
 	}
@@ -282,7 +284,7 @@ func (it *xorIterator) Err() error {
 func (it *xorIterator) Reset(b []byte) {
 	// The first 2 bytes contain chunk headers.
 	// We skip that for actual samples.
-	it.br = newBReader(b[2:])
+	it.br = newBReader(b[chunkHeaderSize:])
 	it.numTotal = binary.BigEndian.Uint16(b)
 
 	it.numRead = 0