Replace cursor direction with a type

tsdb/cursor.go

@@ -5,13 +5,40 @@ import (
 	"container/heap"
 )
 
+// Direction represents a cursor navigation direction.
+type Direction bool
+
+const (
+	// Forward indicates that a cursor will move forward over its values.
+	Forward Direction = true
+	// Reverse indicates that a cursor will move backwards over its values.
+	Reverse Direction = false
+)
+
+func (d Direction) String() string {
+	if d.Forward() {
+		return "forward"
+	}
+	return "reverse"
+}
+
+// Forward returns true if direction is forward
+func (d Direction) Forward() bool {
+	return d == Forward
+}
+
+// Forward returns true if direction is reverse
+func (d Direction) Reverse() bool {
+	return d == Reverse
+}
+
 // MultiCursor returns a single cursor that combines the results of all cursors in order.
 //
 // If the same key is returned from multiple cursors then the first cursor
 // specified will take precendence. A key will only be returned once from the
 // returned cursor.
-func MultiCursor(forward bool, cursors ...Cursor) Cursor {
-	return &multiCursor{cursors: cursors, forward: forward}
+func MultiCursor(d Direction, cursors ...Cursor) Cursor {
+	return &multiCursor{cursors: cursors, direction: d}
 }
 
 // multiCursor represents a cursor that combines multiple cursors into one.
@@ -19,7 +46,7 @@ type multiCursor struct {
 	cursors   []Cursor
 	heap      cursorHeap
 	prev      []byte
-	forward bool
+	direction Direction
 }
 
 // Seek moves the cursor to a given key.
@@ -49,7 +76,7 @@ func (mc *multiCursor) Seek(seek []byte) (key, value []byte) {
 	return mc.pop()
 }
 
-func (mc *multiCursor) Direction() bool { return mc.forward }
+func (mc *multiCursor) Direction() Direction { return mc.direction }
 
 // Next returns the next key/value from the cursor.
 func (mc *multiCursor) Next() (key, value []byte) { return mc.pop() }

tsdb/cursor_test.go

@@ -212,27 +212,27 @@ func TestMultiCursor_Quick(t *testing.T) {
 
 // Cursor represents an in-memory test cursor.
 type Cursor struct {
-	forward bool
+	direction tsdb.Direction
 	items     []CursorItem
 	index     int
 }
 
 // NewCursor returns a new instance of Cursor.
-func NewCursor(forward bool, items []CursorItem) *Cursor {
+func NewCursor(direction tsdb.Direction, items []CursorItem) *Cursor {
 	index := 0
 	sort.Sort(CursorItems(items))
 
-	if !forward {
+	if direction.Reverse() {
 		index = len(items)
 	}
-	return &Cursor{forward: forward, items: items, index: index}
+	return &Cursor{direction: direction, items: items, index: index}
 }
 
-func (c *Cursor) Direction() bool { return c.forward }
+func (c *Cursor) Direction() tsdb.Direction { return c.direction }
 
 // Seek seeks to an item by key.
 func (c *Cursor) Seek(seek []byte) (key, value []byte) {
-	if c.forward {
+	if c.direction.Forward() {
 		return c.seekForward(seek)
 	}
 	return c.seekReverse(seek)
@@ -260,17 +260,17 @@ func (c *Cursor) seekReverse(seek []byte) (key, value []byte) {
 
 // Next returns the next key/value pair.
 func (c *Cursor) Next() (key, value []byte) {
-	if !c.forward && c.index < 0 {
+	if c.direction.Reverse() && c.index < 0 {
 		return nil, nil
 	}
 
-	if c.forward && c.index >= len(c.items) {
+	if c.direction.Forward() && c.index >= len(c.items) {
 		return nil, nil
 	}
 
 	k, v := c.items[c.index].Key, c.items[c.index].Value
 
-	if c.forward {
+	if c.direction.Forward() {
 		c.index++
 	} else {
 		c.index--
@@ -281,7 +281,7 @@ func (c *Cursor) Next() (key, value []byte) {
 // Generate returns a randomly generated cursor. Implements quick.Generator.
 func (c Cursor) Generate(rand *rand.Rand, size int) reflect.Value {
 	c.index = 0
-	c.forward = true
+	c.direction = tsdb.Forward
 
 	c.items = make([]CursorItem, rand.Intn(size))
 	for i := range c.items {

tsdb/engine.go

@@ -123,7 +123,7 @@ func NewEngineOptions() EngineOptions {
 type Tx interface {
 	io.WriterTo
 
-	Cursor(series string, forward bool) Cursor
+	Cursor(series string, direction Direction) Cursor
 	Size() int64
 	Commit() error
 	Rollback() error
@@ -133,7 +133,7 @@ type Tx interface {
 type Cursor interface {
 	Seek(seek []byte) (key, value []byte)
 	Next() (key, value []byte)
-	Direction() bool
+	Direction() Direction
 }
 
 // DedupeEntries returns slices with unique keys (the first 8 bytes).

tsdb/engine/b1/b1.go

@@ -550,7 +550,7 @@ type Tx struct {
 }
 
 // Cursor returns an iterator for a key.
-func (tx *Tx) Cursor(key string, forward bool) tsdb.Cursor {
+func (tx *Tx) Cursor(key string, direction tsdb.Direction) tsdb.Cursor {
 	// Retrieve key bucket.
 	b := tx.Bucket([]byte(key))
 
@@ -591,7 +591,7 @@ type Cursor struct {
 	prev []byte
 }
 
-func (c *Cursor) Direction() bool { return true }
+func (c *Cursor) Direction() tsdb.Direction { return tsdb.Forward }
 
 // Seek moves the cursor to a position and returns the closest key/value pair.
 func (c *Cursor) Seek(seek []byte) (key, value []byte) {

tsdb/engine/bz1/bz1.go

@@ -59,7 +59,7 @@ type WAL interface {
 	WritePoints(points []tsdb.Point, measurementFieldsToSave map[string]*tsdb.MeasurementFields, seriesToCreate []*tsdb.SeriesCreate) error
 	LoadMetadataIndex(index *tsdb.DatabaseIndex, measurementFields map[string]*tsdb.MeasurementFields) error
 	DeleteSeries(keys []string) error
-	Cursor(key string, forward bool) tsdb.Cursor
+	Cursor(key string, direction tsdb.Direction) tsdb.Cursor
 	Open() error
 	Close() error
 	Flush() error
@@ -606,8 +606,8 @@ type Tx struct {
 }
 
 // Cursor returns an iterator for a key.
-func (tx *Tx) Cursor(key string, forward bool) tsdb.Cursor {
-	walCursor := tx.wal.Cursor(key, forward)
+func (tx *Tx) Cursor(key string, direction tsdb.Direction) tsdb.Cursor {
+	walCursor := tx.wal.Cursor(key, direction)
 
 	// Retrieve points bucket. Ignore if there is no bucket.
 	b := tx.Bucket([]byte("points")).Bucket([]byte(key))
@@ -617,14 +617,14 @@ func (tx *Tx) Cursor(key string, forward bool) tsdb.Cursor {
 
 	c := &Cursor{
 		cursor:    b.Cursor(),
-		forward: forward,
+		direction: direction,
 	}
 
-	if !forward {
+	if direction.Reverse() {
 		c.last()
 	}
 
-	return tsdb.MultiCursor(forward, walCursor, c)
+	return tsdb.MultiCursor(direction, walCursor, c)
 }
 
 // Cursor provides ordered iteration across a series.
@@ -632,7 +632,7 @@ type Cursor struct {
 	cursor       *bolt.Cursor
 	buf          []byte // uncompressed buffer
 	off          int    // buffer offset
-	forward      bool
+	direction    tsdb.Direction
 	fieldIndices []int
 	index        int
 }
@@ -642,7 +642,7 @@ func (c *Cursor) last() {
 	c.setBuf(v)
 }
 
-func (c *Cursor) Direction() bool { return c.forward }
+func (c *Cursor) Direction() tsdb.Direction { return c.direction }
 
 // Seek moves the cursor to a position and returns the closest key/value pair.
 func (c *Cursor) Seek(seek []byte) (key, value []byte) {
@@ -678,13 +678,13 @@ func (c *Cursor) seekBuf(seek []byte) (key, value []byte) {
 			return
 		}
 
-		if c.forward && bytes.Compare(buf[0:8], seek) != -1 {
+		if c.direction.Forward() && bytes.Compare(buf[0:8], seek) != -1 {
 			return
-		} else if !c.forward && bytes.Compare(buf[0:8], seek) != 1 {
+		} else if c.direction.Reverse() && bytes.Compare(buf[0:8], seek) != 1 {
 			return
 		}
 
-		if c.forward {
+		if c.direction.Forward() {
 			// Otherwise skip ahead to the next entry.
 			c.off += entryHeaderSize + entryDataSize(buf)
 		} else {
@@ -704,7 +704,7 @@ func (c *Cursor) Next() (key, value []byte) {
 		return nil, nil
 	}
 
-	if c.forward {
+	if c.direction.Forward() {
 		// Move forward to next entry.
 		c.off += entryHeaderSize + entryDataSize(c.buf[c.off:])
 	} else {
@@ -745,7 +745,7 @@ func (c *Cursor) setBuf(block []byte) {
 		log.Printf("block decode error: %s", err)
 	}
 
-	if c.forward {
+	if c.direction.Forward() {
 		c.buf, c.off = buf, 0
 	} else {
 		c.buf, c.off = buf, 0

tsdb/engine/bz1/bz1_test.go

@@ -582,18 +582,18 @@ func (w *EnginePointsWriter) Open() error { return nil }
 
 func (w *EnginePointsWriter) Close() error { return nil }
 
-func (w *EnginePointsWriter) Cursor(key string, forward bool) tsdb.Cursor {
-	return &Cursor{forward: forward}
+func (w *EnginePointsWriter) Cursor(key string, direction tsdb.Direction) tsdb.Cursor {
+	return &Cursor{direction: direction}
 }
 
 func (w *EnginePointsWriter) Flush() error { return nil }
 
 // Cursor represents a mock that implements tsdb.Curosr.
 type Cursor struct {
-	forward bool
+	direction tsdb.Direction
 }
 
-func (c *Cursor) Direction() bool { return c.forward }
+func (c *Cursor) Direction() tsdb.Direction { return c.direction }
 
 func (c *Cursor) Seek(key []byte) ([]byte, []byte) { return nil, nil }
 

tsdb/engine/wal/wal.go

@@ -223,11 +223,11 @@ func (l *Log) Open() error {
 }
 
 // Cursor will return a cursor object to Seek and iterate with Next for the WAL cache for the given
-func (l *Log) Cursor(key string, forward bool) tsdb.Cursor {
+func (l *Log) Cursor(key string, direction tsdb.Direction) tsdb.Cursor {
 	l.mu.RLock()
 	defer l.mu.RUnlock()
 
-	return l.partition([]byte(key)).cursor(key, forward)
+	return l.partition([]byte(key)).cursor(key, direction)
 }
 
 func (l *Log) WritePoints(points []tsdb.Point, fields map[string]*tsdb.MeasurementFields, series []*tsdb.SeriesCreate) error {
@@ -1380,7 +1380,7 @@ func (p *Partition) addToCache(key, data []byte, timestamp int64) {
 }
 
 // cursor will combine the in memory cache and flush cache (if a flush is currently happening) to give a single ordered cursor for the key
-func (p *Partition) cursor(key string, forward bool) *cursor {
+func (p *Partition) cursor(key string, direction tsdb.Direction) *cursor {
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
@@ -1398,7 +1398,7 @@ func (p *Partition) cursor(key string, forward bool) *cursor {
 			c = append(c, entry.points...)
 
 			dedupe := tsdb.DedupeEntries(c)
-			return newCursor(dedupe, forward)
+			return newCursor(dedupe, direction)
 		}
 	}
 
@@ -1410,7 +1410,7 @@ func (p *Partition) cursor(key string, forward bool) *cursor {
 	// build a copy so modifications to the partition don't change the result set
 	a := make([][]byte, len(entry.points))
 	copy(a, entry.points)
-	return newCursor(a, forward)
+	return newCursor(a, direction)
 }
 
 // idFromFileName parses the segment file ID from its name
@@ -1589,22 +1589,22 @@ type entry struct {
 	timestamp int64
 }
 
-// cursor is a forward cursor for a given entry in the cache
+// cursor is a unidirectional iterator for a given entry in the cache
 type cursor struct {
 	cache     [][]byte
 	position  int
-	forward  bool
+	direction tsdb.Direction
 }
 
-func newCursor(cache [][]byte, forward bool) *cursor {
-	c := &cursor{cache: cache, forward: forward}
-	if !forward {
+func newCursor(cache [][]byte, direction tsdb.Direction) *cursor {
+	c := &cursor{cache: cache, direction: direction}
+	if direction.Reverse() {
 		c.position = len(c.cache)
 	}
 	return c
 }
 
-func (c *cursor) Direction() bool { return c.forward }
+func (c *cursor) Direction() tsdb.Direction { return c.direction }
 
 // Seek will point the cursor to the given time (or key)
 func (c *cursor) Seek(seek []byte) (key, value []byte) {
@@ -1619,28 +1619,27 @@ func (c *cursor) Seek(seek []byte) (key, value []byte) {
 // Next moves the cursor to the next key/value. will return nil if at the end
 func (c *cursor) Next() (key, value []byte) {
 
-	if !c.forward && c.position >= len(c.cache) {
+	if c.direction.Reverse() && c.position >= len(c.cache) {
 		c.position--
 	}
 
-	if c.forward && c.position >= len(c.cache) {
+	if c.direction.Forward() && c.position >= len(c.cache) {
 		return nil, nil
 	}
 
-	if !c.forward && c.position < 0 {
+	if c.direction.Reverse() && c.position < 0 {
 		return nil, nil
 	}
 
 	v := c.cache[c.position]
 
-	if c.forward {
+	if c.direction.Forward() {
 		c.position++
 	} else {
 		c.position--
 	}
 
 	return v[0:8], v[8:]
-
 }
 
 // seriesAndFields is a data struct to serialize new series and fields

tsdb/mapper.go

@@ -218,9 +218,13 @@ func (lm *SelectMapper) Open() error {
 			}
 		}
 
-		forward := true
+		direction := Forward
 		if len(lm.selectStmt.SortFields) > 0 {
-			forward = lm.selectStmt.SortFields[0].Ascending
+			if lm.selectStmt.SortFields[0].Ascending {
+				direction = Forward
+			} else {
+				direction = Reverse
+			}
 		}
 
 		// Create all cursors for reading the data from this shard.
@@ -228,7 +232,7 @@ func (lm *SelectMapper) Open() error {
 			cursors := []*seriesCursor{}
 
 			for i, key := range t.SeriesKeys {
-				c := lm.tx.Cursor(key, forward)
+				c := lm.tx.Cursor(key, direction)
 				if c == nil {
 					// No data exists for this key.
 					continue
@@ -245,7 +249,7 @@ func (lm *SelectMapper) Open() error {
 				for i := 0; i < len(tsc.cursors); i++ {
 					var k int64
 					var v []byte
-					if forward {
+					if direction == Forward {
 						k, v = tsc.cursors[i].SeekTo(lm.queryTMin)
 						if k == -1 {
 							k, v = tsc.cursors[i].Next()