added KVReader.MultiGet() method

index/store/boltdb/reader.go

@@ -30,6 +30,10 @@ func (r *Reader) Get(key []byte) ([]byte, error) {
 	return rv, nil
 }
 
+func (r *Reader) MultiGet(keys [][]byte) ([][]byte, error) {
+	return store.MultiGet(r, keys)
+}
+
 func (r *Reader) PrefixIterator(prefix []byte) store.KVIterator {
 	cursor := r.bucket.Cursor()
 

index/store/goleveldb/reader.go

@@ -28,6 +28,10 @@ func (r *Reader) Get(key []byte) ([]byte, error) {
 	return b, err
 }
 
+func (r *Reader) MultiGet(keys [][]byte) ([][]byte, error) {
+	return store.MultiGet(r, keys)
+}
+
 func (r *Reader) PrefixIterator(prefix []byte) store.KVIterator {
 	byteRange := util.BytesPrefix(prefix)
 	iter := r.snapshot.NewIterator(byteRange, r.store.defaultReadOptions)

index/store/gtreap/reader.go

@@ -35,6 +35,10 @@ func (w *Reader) Get(k []byte) (v []byte, err error) {
 	return nil, nil
 }
 
+func (r *Reader) MultiGet(keys [][]byte) ([][]byte, error) {
+	return store.MultiGet(r, keys)
+}
+
 func (w *Reader) PrefixIterator(k []byte) store.KVIterator {
 	rv := Iterator{
 		t:      w.t,

index/store/kvstore.go

@@ -40,6 +40,9 @@ type KVReader interface {
 	// The caller owns the bytes returned.
 	Get(key []byte) ([]byte, error)
 
+	// MultiGet retrieves multiple values in one call.
+	MultiGet(keys [][]byte) ([][]byte, error)
+
 	// PrefixIterator returns a KVIterator that will
 	// visit all K/V pairs with the provided prefix
 	PrefixIterator(prefix []byte) KVIterator

index/store/metrics/reader.go

@@ -17,6 +17,16 @@ func (r *Reader) Get(key []byte) (v []byte, err error) {
 	return
 }
 
+func (r *Reader) MultiGet(keys [][]byte) (vals [][]byte, err error) {
+	r.s.TimerReaderMultiGet.Time(func() {
+		vals, err = r.o.MultiGet(keys)
+		if err != nil {
+			r.s.AddError("Reader.MultiGet", err, nil)
+		}
+	})
+	return
+}
+
 func (r *Reader) PrefixIterator(prefix []byte) (i store.KVIterator) {
 	r.s.TimerReaderPrefixIterator.Time(func() {
 		i = &Iterator{s: r.s, o: r.o.PrefixIterator(prefix)}

index/store/metrics/store.go

@@ -33,6 +33,7 @@ type Store struct {
 	o store.KVStore
 
 	TimerReaderGet            metrics.Timer
+	TimerReaderMultiGet       metrics.Timer
 	TimerReaderPrefixIterator metrics.Timer
 	TimerReaderRangeIterator  metrics.Timer
 	TimerWriterExecuteBatch   metrics.Timer
@@ -71,6 +72,7 @@ func New(mo store.MergeOperator, config map[string]interface{}) (store.KVStore,
 		o: kvs,
 
 		TimerReaderGet:            metrics.NewTimer(),
+		TimerReaderMultiGet:       metrics.NewTimer(),
 		TimerReaderPrefixIterator: metrics.NewTimer(),
 		TimerReaderRangeIterator:  metrics.NewTimer(),
 		TimerWriterExecuteBatch:   metrics.NewTimer(),
@@ -141,6 +143,11 @@ func (s *Store) WriteJSON(w io.Writer) (err error) {
 		return
 	}
 	WriteTimerJSON(w, s.TimerReaderGet)
+	_, err = w.Write([]byte(`,"TimerReaderMultiGet":`))
+	if err != nil {
+		return
+	}
+	WriteTimerJSON(w, s.TimerReaderMultiGet)
 	_, err = w.Write([]byte(`,"TimerReaderPrefixIterator":`))
 	if err != nil {
 		return

index/store/multiget.go

@@ -0,0 +1,28 @@
+//  Copyright (c) 2016 Couchbase, Inc.
+//  Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+//  except in compliance with the License. You may obtain a copy of the License at
+//    http://www.apache.org/licenses/LICENSE-2.0
+//  Unless required by applicable law or agreed to in writing, software distributed under the
+//  License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+//  either express or implied. See the License for the specific language governing permissions
+//  and limitations under the License.
+
+package store
+
+// MultiGet is a helper function to retrieve mutiple keys from a
+// KVReader, and might be used by KVStore implementations that don't
+// have a native multi-get facility.
+func MultiGet(kvreader KVReader, keys [][]byte) ([][]byte, error) {
+	vals := make([][]byte, 0, len(keys))
+
+	for i, key := range keys {
+		val, err := kvreader.Get(key)
+		if err != nil {
+			return nil, err
+		}
+
+		vals[i] = val
+	}
+
+	return vals, nil
+}

index/store/null/null.go

@@ -40,6 +40,10 @@ func (r *reader) Get(key []byte) ([]byte, error) {
 	return nil, nil
 }
 
+func (r *reader) MultiGet(keys [][]byte) ([][]byte, error) {
+	return make([][]byte, len(keys)), nil
+}
+
 func (r *reader) PrefixIterator(prefix []byte) store.KVIterator {
 	return &iterator{}
 }