From 1e0edf367b872a8be511b884f493fb035f71bc9d Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Fri, 9 Dec 2016 21:23:34 +0100
Subject: [PATCH] Write index with symbol table

---
 db.go     | 23 ++++++++++++----
 writer.go | 79 ++++++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 87 insertions(+), 15 deletions(-)

diff --git a/db.go b/db.go
index e65ac877b..30f16ffb5 100644
--- a/db.go
+++ b/db.go
@@ -267,19 +267,32 @@ func (s *SeriesShard) persist() error {
 		return err
 	}
 
-	f, err := os.Create(filepath.Join(p, "series"))
+	sf, err := os.Create(filepath.Join(p, "series"))
+	if err != nil {
+		return err
+	}
+	xf, err := os.Create(filepath.Join(p, "index"))
 	if err != nil {
 		return err
 	}
 
-	w := newSeriesWriter(f, s.head.baseTimestamp)
-	defer w.Close()
+	iw := newIndexWriter(xf)
+	sw := newSeriesWriter(sf, iw, s.head.baseTimestamp)
+
+	defer sw.Close()
+	defer iw.Close()
 
 	for _, cd := range head.index.forward {
-		w.WriteSeries(cd.lset, []*chunkDesc{cd})
+		if err := sw.WriteSeries(cd.lset, []*chunkDesc{cd}); err != nil {
+			return err
+		}
 	}
 
-	sz := fmt.Sprintf("%fMiB", float64(w.Size())/1024/1024)
+	if err := iw.WriteStats(nil); err != nil {
+		return err
+	}
+
+	sz := fmt.Sprintf("%fMiB", float64(sw.Size()+iw.Size())/1024/1024)
 
 	s.logger.With("size", sz).
 		With("samples", head.samples).
diff --git a/writer.go b/writer.go
index e78a1ab7e..eebb45801 100644
--- a/writer.go
+++ b/writer.go
@@ -1,9 +1,11 @@
 package tsdb
 
 import (
+	"encoding/binary"
 	"hash/crc32"
 	"io"
 	"os"
+	"sort"
 	"unsafe"
 )
 
@@ -37,15 +39,13 @@ type seriesWriter struct {
 
 	baseTimestamp int64
 	index         IndexWriter
-
-	chunkOffsets  map[uint32][]uint32
-	seriesOffsets map[uint32]uint32
 }
 
-func newSeriesWriter(w io.Writer, base int64) *seriesWriter {
+func newSeriesWriter(w io.Writer, index IndexWriter, base int64) *seriesWriter {
 	return &seriesWriter{
 		w:             w,
 		n:             0,
+		index:         index,
 		baseTimestamp: base,
 	}
 }
@@ -148,9 +148,6 @@ type IndexWriter interface {
 	// WriteStats writes final stats for the indexed block.
 	WriteStats(*BlockStats) error
 
-	// WriteSymbols serializes all encountered string symbols.
-	WriteSymbols([]string) error
-
 	// WriteLabelIndex serializes an index from label names to values.
 	// The passed in values chained tuples of strings of the length of names.
 	WriteLabelIndex(names []string, values []string) error
@@ -164,7 +161,7 @@ type IndexWriter interface {
 	// Size returns the size of the data written so far.
 	Size() int64
 
-	// Closes writes any finalization and closes theresources associated with
+	// Close writes any finalization and closes theresources associated with
 	// the underlying writer.
 	Close() error
 }
@@ -177,19 +174,80 @@ type indexWriter struct {
 
 	series  []Labels
 	offsets [][]ChunkOffset
+
+	symbols map[string]uint32
+}
+
+func newIndexWriter(w io.Writer) *indexWriter {
+	return &indexWriter{
+		w:       w,
+		n:       0,
+		symbols: make(map[string]uint32),
+	}
+}
+
+func (w *indexWriter) write(wr io.Writer, b []byte) error {
+	n, err := wr.Write(b)
+	w.n += int64(n)
+	return err
+}
+
+func (w *indexWriter) writeMeta() error {
+	meta := &meta{magic: MagicSeries, flag: flagStd}
+	metab := ((*[metaSize]byte)(unsafe.Pointer(meta)))[:]
+
+	return w.write(w.w, metab)
 }
 
 func (w *indexWriter) AddOffsets(lset Labels, offsets ...ChunkOffset) {
 	w.series = append(w.series, lset)
 	w.offsets = append(w.offsets, offsets)
+
+	// Populate the symbol table from all label sets we have to reference.
+	for _, l := range lset {
+		w.symbols[l.Name] = 0
+		w.symbols[l.Value] = 0
+	}
 }
 
 func (w *indexWriter) WriteStats(*BlockStats) error {
+	if w.n == 0 {
+		if err := w.writeMeta(); err != nil {
+			return err
+		}
+		if err := w.writeSymbols(); err != nil {
+			return err
+		}
+	}
 	return nil
 }
 
-func (w *indexWriter) WriteSymbols(symbols []string) error {
-	return nil
+func (w *indexWriter) writeSymbols() error {
+	// Generate sorted list of strings we will store as reference table.
+	symbols := make([]string, 0, len(w.symbols))
+	for s := range w.symbols {
+		symbols = append(symbols, s)
+	}
+	sort.Strings(symbols)
+
+	h := crc32.NewIEEE()
+	wr := io.MultiWriter(h, w.w)
+
+	buf := make([]byte, binary.MaxVarintLen32)
+
+	for _, s := range symbols {
+		n := binary.PutUvarint(buf, uint64(len(s)))
+		w.symbols[s] = uint32(w.n)
+
+		if err := w.write(wr, buf[:n]); err != nil {
+			return err
+		}
+		if err := w.write(wr, []byte(s)); err != nil {
+			return err
+		}
+	}
+
+	return w.write(w.w, h.Sum(nil))
 }
 
 func (w *indexWriter) WriteLabelIndex(names []string, values []string) error {
@@ -207,6 +265,7 @@ func (w *indexWriter) WritePostings(name, value string, it Iterator) error {
 func (w *indexWriter) Size() int64 {
 	return w.n
 }
+
 func (w *indexWriter) Close() error {
 	if f, ok := w.w.(*os.File); ok {
 		if err := f.Sync(); err != nil {