Append to chunks cannot error

chunks/chunk.go

@@ -2,7 +2,6 @@ package chunks
 
 import (
 	"encoding/binary"
-	"errors"
 	"fmt"
 )
 
@@ -25,12 +24,6 @@ const (
 	EncXOR
 )
 
-var (
-	// ErrChunkFull is returned if the remaining size of a chunk cannot
-	// fit the appended data.
-	ErrChunkFull = errors.New("chunk full")
-)
-
 // Chunk holds a sequence of sample pairs that can be iterated over and appended to.
 type Chunk interface {
 	Bytes() []byte
@@ -51,31 +44,14 @@ func FromData(e Encoding, d []byte) (Chunk, error) {
 	return nil, fmt.Errorf("unknown chunk encoding: %d", e)
 }
 
-// Iterator provides iterating access over sample pairs in chunks.
-type Iterator interface {
-	StreamingIterator
-
-	// Seek(t int64) bool
-	// SeekBefore(t int64) bool
-	// Next() bool
-	// Values() (int64, float64)
-	// Err() error
-}
-
 // Appender adds sample pairs to a chunk.
 type Appender interface {
-	Append(int64, float64) error
+	Append(int64, float64)
 }
 
-// StreamingIterator is a simple iterator that can only get the next value.
-type StreamingIterator interface {
+// Iterator is a simple iterator that can only get the next value.
+type Iterator interface {
 	Values() (int64, float64)
 	Err() error
 	Next() bool
 }
-
-// fancyIterator wraps a StreamingIterator and implements a regular
-// Iterator with it.
-type fancyIterator struct {
-	StreamingIterator
-}

chunks/chunk_test.go

@@ -16,12 +16,12 @@ type pair struct {
 }
 
 func TestChunk(t *testing.T) {
-	for enc, nc := range map[Encoding]func(sz int) Chunk{
-		EncXOR: func(sz int) Chunk { return NewXORChunk(sz) },
+	for enc, nc := range map[Encoding]func() Chunk{
+		EncXOR: func() Chunk { return NewXORChunk() },
 	} {
 		t.Run(fmt.Sprintf("%s", enc), func(t *testing.T) {
 			for range make([]struct{}, 1) {
-				c := nc(rand.Intn(1024))
+				c := nc()
 				if err := testChunk(c); err != nil {
 					t.Fatal(err)
 				}
@@ -59,13 +59,7 @@ func testChunk(c Chunk) error {
 			}
 		}
 
-		err = app.Append(ts, v)
-		if err != nil {
-			if err == ErrChunkFull {
-				break
-			}
-			return err
-		}
+		app.Append(ts, v)
 		exp = append(exp, pair{t: ts, v: v})
 		// fmt.Println("appended", len(c.Bytes()), c.Bytes())
 	}
@@ -85,7 +79,7 @@ func testChunk(c Chunk) error {
 	return nil
 }
 
-func benchmarkIterator(b *testing.B, newChunk func(int) Chunk) {
+func benchmarkIterator(b *testing.B, newChunk func() Chunk) {
 	var (
 		t = int64(1234123324)
 		v = 1243535.123
@@ -101,19 +95,20 @@ func benchmarkIterator(b *testing.B, newChunk func(int) Chunk) {
 
 	var chunks []Chunk
 	for i := 0; i < b.N; {
-		c := newChunk(1024)
+		c := newChunk()
 
 		a, err := c.Appender()
 		if err != nil {
 			b.Fatalf("get appender: %s", err)
 		}
+		j := 0
 		for _, p := range exp {
-			if err := a.Append(p.t, p.v); err == ErrChunkFull {
+			if j > 250 {
 				break
-			} else if err != nil {
-				b.Fatal(err)
 			}
+			a.Append(p.t, p.v)
 			i++
+			j++
 		}
 		chunks = append(chunks, c)
 	}
@@ -141,18 +136,18 @@ func benchmarkIterator(b *testing.B, newChunk func(int) Chunk) {
 }
 
 func BenchmarkXORIterator(b *testing.B) {
-	benchmarkIterator(b, func(sz int) Chunk {
-		return NewXORChunk(sz)
+	benchmarkIterator(b, func() Chunk {
+		return NewXORChunk()
 	})
 }
 
 func BenchmarkXORAppender(b *testing.B) {
-	benchmarkAppender(b, func(sz int) Chunk {
-		return NewXORChunk(sz)
+	benchmarkAppender(b, func() Chunk {
+		return NewXORChunk()
 	})
 }
 
-func benchmarkAppender(b *testing.B, newChunk func(int) Chunk) {
+func benchmarkAppender(b *testing.B, newChunk func() Chunk) {
 	var (
 		t = int64(1234123324)
 		v = 1243535.123
@@ -171,19 +166,20 @@ func benchmarkAppender(b *testing.B, newChunk func(int) Chunk) {
 
 	var chunks []Chunk
 	for i := 0; i < b.N; {
-		c := newChunk(1024)
+		c := newChunk()
 
 		a, err := c.Appender()
 		if err != nil {
 			b.Fatalf("get appender: %s", err)
 		}
+		j := 0
 		for _, p := range exp {
-			if err := a.Append(p.t, p.v); err == ErrChunkFull {
+			if j > 250 {
 				break
-			} else if err != nil {
-				b.Fatal(err)
 			}
+			a.Append(p.t, p.v)
 			i++
+			j++
 		}
 		chunks = append(chunks, c)
 	}

chunks/xor.go

@@ -11,16 +11,14 @@ import (
 type XORChunk struct {
 	b   *bstream
 	num uint16
-	sz  int
 }
 
 // NewXORChunk returns a new chunk with XOR encoding of the given size.
-func NewXORChunk(size int) *XORChunk {
+func NewXORChunk() *XORChunk {
 	b := make([]byte, 2, 128)
 
 	return &XORChunk{
 		b:   &bstream{stream: b, count: 0},
-		sz:  size,
 		num: 0,
 	}
 }
@@ -78,7 +76,7 @@ func (c *XORChunk) iterator() *xorIterator {
 
 // Iterator implements the Chunk interface.
 func (c *XORChunk) Iterator() Iterator {
-	return fancyIterator{c.iterator()}
+	return c.iterator()
 }
 
 type xorAppender struct {
@@ -93,9 +91,8 @@ type xorAppender struct {
 	trailing uint8
 }
 
-func (a *xorAppender) Append(t int64, v float64) error {
+func (a *xorAppender) Append(t int64, v float64) {
 	var tDelta uint64
-	l := len(a.b.bytes())
 
 	if a.c.num == 0 {
 		buf := make([]byte, binary.MaxVarintLen64)
@@ -140,19 +137,10 @@ func (a *xorAppender) Append(t int64, v float64) error {
 		a.writeVDelta(v)
 	}
 
-	if len(a.b.bytes()) > a.c.sz {
-		// If the appended data exceeded the size limit, we truncate
-		// the underlying data slice back to the length we started with.
-		a.b.stream = a.b.stream[:l]
-		return ErrChunkFull
-	}
-
 	a.t = t
 	a.v = v
 	a.c.num++
 	a.tDelta = tDelta
-
-	return nil
 }
 
 func bitRange(x int64, nbits uint8) bool {

db.go

@@ -413,23 +413,15 @@ type chunkDesc struct {
 	app chunks.Appender // Current appender for the chunks.
 }
 
-func (cd *chunkDesc) append(ts int64, v float64) (err error) {
-	if cd.app == nil {
-		cd.app, err = cd.chunk.Appender()
-		if err != nil {
-			return err
-		}
+func (cd *chunkDesc) append(ts int64, v float64) {
+	if cd.numSamples == 0 {
 		cd.firsTimestamp = ts
 	}
-	if err := cd.app.Append(ts, v); err != nil {
-		return err
-	}
+	cd.app.Append(ts, v)
 
 	cd.lastTimestamp = ts
 	cd.lastValue = v
 	cd.numSamples++
-
-	return nil
 }
 
 // The MultiError type implements the error interface, and contains the

head.go

@@ -1,7 +1,6 @@
 package tsdb
 
 import (
-	"math"
 	"os"
 	"sort"
 	"sync"
@@ -51,9 +50,7 @@ func OpenHeadBlock(dir string, baseTime int64) (*HeadBlock, error) {
 			b.create(lset.Hash(), lset)
 		},
 		sample: func(s hashedSample) {
-			if err := b.descs[s.ref].append(s.t, s.v); err != nil {
-				panic(err) // TODO(fabxc): cannot actually error
-			}
+			b.descs[s.ref].append(s.t, s.v)
 			b.stats.SampleCount++
 		},
 	})
@@ -151,9 +148,16 @@ func (h *HeadBlock) get(hash uint64, lset labels.Labels) (*chunkDesc, uint32) {
 }
 
 func (h *HeadBlock) create(hash uint64, lset labels.Labels) *chunkDesc {
+	var err error
+
 	cd := &chunkDesc{
 		lset:  lset,
-		chunk: chunks.NewXORChunk(int(math.MaxInt64)),
+		chunk: chunks.NewXORChunk(),
+	}
+	cd.app, err = cd.chunk.Appender()
+	if err != nil {
+		// Getting an Appender for a new chunk must not panic.
+		panic(err)
 	}
 	// Index the new chunk.
 	ref := len(h.descs)
@@ -226,13 +230,8 @@ func (h *HeadBlock) appendBatch(samples []hashedSample, appended prometheus.Coun
 		h.create(newHashes[i], s)
 	}
 
-	var merr MultiError
 	for _, s := range samples {
-		// TODO(fabxc): ensure that this won't be able to actually error in practice.
-		if err := h.descs[s.ref].append(s.t, s.v); err != nil {
-			merr.Add(err)
-			continue
-		}
+		h.descs[s.ref].append(s.t, s.v)
 
 		appended.Inc()
 		h.stats.SampleCount++
@@ -242,7 +241,7 @@ func (h *HeadBlock) appendBatch(samples []hashedSample, appended prometheus.Coun
 		}
 	}
 
-	return merr.Err()
+	return nil
 }
 
 func (h *HeadBlock) persist(p string) (int64, error) {