support using end key on forestdb iterator for term freq lookup

also additoanl forestdb configs

index/store/forestdb/iterator.go

@@ -43,6 +43,16 @@ func newIteratorWithSnapshot(store *Store, snapshot *forestdb.KVStore) *Iterator
 	return &rv
 }
 
+func newIteratorWithSnapshotAndRange(store *Store, snapshot *forestdb.KVStore, start, end []byte) *Iterator {
+	itr, err := snapshot.IteratorInit(start, end, forestdb.ITR_NONE)
+	rv := Iterator{
+		store:    store,
+		iterator: itr,
+		valid:    err == nil,
+	}
+	return &rv
+}
+
 func (i *Iterator) SeekFirst() {
 	err := i.iterator.SeekMin()
 	if err != nil {

index/store/forestdb/reader.go

@@ -52,6 +52,12 @@ func (r *Reader) Iterator(key []byte) store.KVIterator {
 	return rv
 }
 
+func (r *Reader) RangeIterator(start, end []byte) store.KVIterator {
+	rv := newIteratorWithSnapshotAndRange(r.store, r.snapshot, start, end)
+	rv.Seek(start)
+	return rv
+}
+
 func (r *Reader) Close() error {
 	return r.snapshot.Close()
 }

index/store/forestdb/store.go

@@ -42,6 +42,7 @@ func New(path string, createIfMissing bool,
 
 	forestDBDefaultConfig := forestdb.DefaultConfig()
 	forestDBDefaultConfig.SetCompactionMode(forestdb.COMPACT_AUTO)
+	forestDBDefaultConfig.SetMultiKVInstances(false)
 	forestDBConfig, err := applyConfig(forestDBDefaultConfig, config)
 	if err != nil {
 		return nil, err
@@ -284,5 +285,8 @@ func applyConfig(c *forestdb.Config, config map[string]interface{}) (
 	if v, exists := config["walThreshold"].(float64); exists {
 		c.SetWalThreshold(uint64(v))
 	}
+	if v, exists := config["maxWriterLockProb"].(float64); exists {
+		c.SetMaxWriterLockProb(uint8(v))
+	}
 	return c, nil
 }

index/store/kvstore.go

@@ -51,3 +51,8 @@ type KVReader interface {
 	Iterator(key []byte) KVIterator
 	Close() error
 }
+
+type RangeIterable interface {
+	// iterates keys >= start and < end
+	RangeIterator(start, end []byte) KVIterator
+}

index/upside_down/reader.go

@@ -46,7 +46,16 @@ func newUpsideDownCouchTermFieldReader(indexReader *IndexReader, term []byte, fi
 
 	tfr := NewTermFrequencyRow(term, field, "", 0, 0)
 	readerPrefix := tfr.Key()
-	it := indexReader.kvreader.Iterator(readerPrefix)
+
+	var it store.KVIterator
+	switch kvreader := indexReader.kvreader.(type) {
+	case store.RangeIterable:
+		etfr := NewTermFrequencyRow(term[:len(term)-1], field, "", 0, 0)
+		nextTermPrefix := etfr.Key()
+		it = kvreader.RangeIterator(readerPrefix, nextTermPrefix)
+	default:
+		it = kvreader.Iterator(readerPrefix)
+	}
 
 	return &UpsideDownCouchTermFieldReader{
 		indexReader:  indexReader,