Update engine to put index at the end of data files

tsdb/engine/pd1/pd1.go

@@ -58,6 +58,8 @@ const (
 
 	// MAP_POPULATE is for the mmap syscall. For some reason this isn't defined in golang's syscall
 	MAP_POPULATE = 0x8000
+
+	magicNumber uint32 = 0x16D116D1
 )
 
 // Ensure Engine implements the interface.
@@ -308,6 +310,8 @@ func (e *Engine) WriteAndCompact(pointsByKey map[string]Values, measurementField
 	return nil
 }
 
+// rewriteFile will read in the old data file, if provided and merge the values
+// in the passed map into a new data file
 func (e *Engine) rewriteFile(oldDF *dataFile, valuesByID map[uint64]Values) error {
 	// we need the values in sorted order so that we can merge them into the
 	// new file as we read the old file
@@ -351,31 +355,15 @@ func (e *Engine) rewriteFile(oldDF *dataFile, valuesByID map[uint64]Values) erro
 		return err
 	}
 
-	// write the header of the file and keep track of the current file position
-	currentPosition := uint32(4)
-	// series count
-	if _, err := f.Write(u32tob(uint32(len(ids)))); err != nil {
+	// write the magic number
+	if _, err := f.Write(u32tob(magicNumber)); err != nil {
 		f.Close()
 		return err
 	}
-	// empty min time and max time
-	currentPosition += 16
-	if _, err := f.Write([]byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}); err != nil {
-		f.Close()
-		return nil
-	}
-
-	// write the series ids and empty starting positions
-	for _, id := range ids {
-		if _, err := f.Write(append(u64tob(id), []byte{0x00, 0x00, 0x00, 0x00}...)); err != nil {
-			f.Close()
-			return err
-		}
-		currentPosition += 12
-	}
 
 	// now combine the old file data with the new values, keeping track of
 	// their positions
+	currentPosition := uint32(4)
 	newPositions := make([]uint32, len(ids))
 	buf := make([]byte, DefaultMaxPointsPerBlock*20)
 	for i, id := range ids {
@@ -487,25 +475,31 @@ func (e *Engine) rewriteFile(oldDF *dataFile, valuesByID map[uint64]Values) erro
 		}
 	}
 
-	// write out the times and positions
-	if _, err := f.Seek(4, 0); err != nil {
-		f.Close()
-		return err
+	// write the file index, starting with the series ids and their positions
+	for i, id := range ids {
+		if _, err := f.Write(u64tob(id)); err != nil {
+			f.Close()
+			return err
+		}
+		if _, err := f.Write(u32tob(newPositions[i])); err != nil {
+			f.Close()
+			return err
+		}
 	}
+
+	// write the min time, max time
 	if _, err := f.Write(append(u64tob(uint64(minTime)), u64tob(uint64(maxTime))...)); err != nil {
 		f.Close()
 		return err
 	}
-	for _, pos := range newPositions {
-		if _, err := f.Seek(8, 1); err != nil {
-			f.Close()
-			return err
-		}
 
-		if _, err := f.Write(u32tob(pos)); err != nil {
-			return err
-		}
+	// series count
+	if _, err := f.Write(u32tob(uint32(len(ids)))); err != nil {
+		f.Close()
+		return err
 	}
+
+	// sync it and see4k back to the beginning to hand off to the mmap
 	if err := f.Sync(); err != nil {
 		return err
 	}
@@ -888,23 +882,24 @@ func (d *dataFile) close() error {
 }
 
 func (d *dataFile) MinTime() int64 {
-	return int64(btou64(d.mmap[4:12]))
+	return int64(btou64(d.mmap[d.size-20 : d.size-12]))
 }
 
 func (d *dataFile) MaxTime() int64 {
-	return int64(btou64(d.mmap[12:20]))
+	return int64(btou64(d.mmap[d.size-12 : d.size-4]))
 }
 
 func (d *dataFile) SeriesCount() uint32 {
-	return btou32(d.mmap[:4])
+	return btou32(d.mmap[d.size-4:])
 }
 
 func (d *dataFile) IDToPosition() map[uint64]uint32 {
 	count := int(d.SeriesCount())
 	m := make(map[uint64]uint32)
 
+	indexStart := d.size - uint32(count*12+20)
 	for i := 0; i < count; i++ {
-		offset := 20 + (i * 12)
+		offset := indexStart + uint32(i*12)
 		id := btou64(d.mmap[offset : offset+8])
 		pos := btou32(d.mmap[offset+8 : offset+12])
 		m[id] = pos
@@ -917,15 +912,17 @@ func (d *dataFile) IDToPosition() map[uint64]uint32 {
 // first block for the given ID. If zero is returned the ID doesn't
 // have any data in this file.
 func (d *dataFile) StartingPositionForID(id uint64) uint32 {
-	seriesCount := d.SeriesCount()
 
-	min := 0
-	max := int(seriesCount)
+	seriesCount := d.SeriesCount()
+	indexStart := d.size - uint32(seriesCount*12+20)
+
+	min := uint32(0)
+	max := uint32(seriesCount)
 
 	for min < max {
 		mid := (max-min)/2 + min
 
-		offset := mid*seriesHeaderSize + fileHeaderSize
+		offset := mid*seriesHeaderSize + indexStart
 		checkID := btou64(d.mmap[offset : offset+8])
 
 		if checkID == id {
@@ -1066,6 +1063,7 @@ func (c *cursor) Next() (key, value []byte) {
 
 			startingPos := f.StartingPositionForID(c.id)
 			if startingPos == 0 {
+				c.filesPos++
 				continue
 			}
 			c.f = f
@@ -1119,7 +1117,7 @@ func btou32(b []byte) uint32 {
 func hashSeriesField(key string) uint64 {
 	h := fnv.New64a()
 	h.Write([]byte(key))
-	return h.Sum64()
+	return h.Sum64() % 100
 }
 
 // seriesFieldKey combine a series key and field name for a unique string to be hashed to a numeric ID