diff --git a/ledis/const.go b/ledis/const.go
index 393b97d..3c9b99c 100644
--- a/ledis/const.go
+++ b/ledis/const.go
@@ -104,7 +104,7 @@ var (
 )
 
 const (
-	MaxDatabases int = 16
+	MaxDatabases int = 10240
 
 	//max key size
 	MaxKeySize int = 1024
diff --git a/ledis/event.go b/ledis/event.go
index b9a4833..1f5b792 100644
--- a/ledis/event.go
+++ b/ledis/event.go
@@ -18,7 +18,11 @@ func formatEventKey(buf []byte, k []byte) ([]byte, error) {
 	buf = append(buf, fmt.Sprintf("%s ", TypeName[k[1]])...)
 
 	db := new(DB)
-	db.index = k[0]
+	index, _, err := decodeDBIndex(k)
+	if err != nil {
+		return nil, err
+	}
+	db.setIndex(index)
 
 	//to do format at respective place
 
diff --git a/ledis/ledis_db.go b/ledis/ledis_db.go
index 21811b5..3ceeaae 100644
--- a/ledis/ledis_db.go
+++ b/ledis/ledis_db.go
@@ -1,6 +1,8 @@
 package ledis
 
 import (
+	"bytes"
+	"encoding/binary"
 	"fmt"
 	"github.com/siddontang/ledisdb/store"
 	"sync"
@@ -30,7 +32,10 @@ type DB struct {
 
 	bucket ibucket
 
-	index uint8
+	index int
+
+	// buffer to store index varint
+	indexVarBuf []byte
 
 	kvBatch   *batch
 	listBatch *batch
@@ -56,7 +61,7 @@ func (l *Ledis) newDB(index int) *DB {
 	d.bucket = d.sdb
 
 	//	d.status = DBAutoCommit
-	d.index = uint8(index)
+	d.setIndex(index)
 
 	d.kvBatch = d.newBatch()
 	d.listBatch = d.newBatch()
@@ -72,6 +77,37 @@ func (l *Ledis) newDB(index int) *DB {
 	return d
 }
 
+func decodeDBIndex(buf []byte) (int, int, error) {
+	index, n := binary.Uvarint(buf)
+	if n == 0 {
+		return 0, 0, fmt.Errorf("buf is too small to save index")
+	} else if n < 0 {
+		return 0, 0, fmt.Errorf("value larger than 64 bits")
+	} else if index > uint64(MaxDatabases) {
+		return 0, 0, fmt.Errorf("value %d is larger than max databases %d", index, MaxDatabases)
+	}
+	return int(index), n, nil
+}
+
+func (db *DB) setIndex(index int) {
+	db.index = index
+	// the most size for varint is 10 bytes
+	buf := make([]byte, 10)
+	n := binary.PutUvarint(buf, uint64(index))
+
+	db.indexVarBuf = buf[0:n]
+}
+
+func (db *DB) checkKeyIndex(buf []byte) (int, error) {
+	if len(buf) < len(db.indexVarBuf) {
+		return 0, fmt.Errorf("key is too small")
+	} else if !bytes.Equal(db.indexVarBuf, buf[0:len(db.indexVarBuf)]) {
+		return 0, fmt.Errorf("invalid db index")
+	}
+
+	return len(db.indexVarBuf), nil
+}
+
 func (db *DB) newTTLChecker() *ttlChecker {
 	c := new(ttlChecker)
 	c.db = db
diff --git a/ledis/ledis_test.go b/ledis/ledis_test.go
index 51e4d0d..a0c9879 100644
--- a/ledis/ledis_test.go
+++ b/ledis/ledis_test.go
@@ -37,24 +37,85 @@ func TestDB(t *testing.T) {
 func TestSelect(t *testing.T) {
 	db0, _ := testLedis.Select(0)
 	db1, _ := testLedis.Select(1)
+	db1024, _ := testLedis.Select(1024)
 
-	key0 := []byte("db0_test_key")
-	key1 := []byte("db1_test_key")
+	testSelect(t, db0)
+	testSelect(t, db1)
+	testSelect(t, db1024)
+}
 
-	db0.Set(key0, []byte("0"))
-	db1.Set(key1, []byte("1"))
-
-	if v, err := db0.Get(key0); err != nil {
+func testSelect(t *testing.T, db *DB) {
+	key := []byte("test_select_key")
+	value := []byte("value")
+	if err := db.Set(key, value); err != nil {
 		t.Fatal(err)
-	} else if string(v) != "0" {
+	}
+
+	if v, err := db.Get(key); err != nil {
+		t.Fatal(err)
+	} else if string(v) != string(value) {
 		t.Fatal(string(v))
 	}
 
-	if v, err := db1.Get(key1); err != nil {
+	if _, err := db.Expire(key, 100); err != nil {
 		t.Fatal(err)
-	} else if string(v) != "1" {
+	}
+
+	if _, err := db.TTL(key); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := db.Persist(key); err != nil {
+		t.Fatal(err)
+	}
+
+	key = []byte("test_select_list_key")
+	if _, err := db.LPush(key, value); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := db.LRange(key, 0, 100); err != nil {
+		t.Fatal(err)
+	}
+
+	if v, err := db.LPop(key); err != nil {
+		t.Fatal(err)
+	} else if string(v) != string(value) {
 		t.Fatal(string(v))
 	}
+
+	key = []byte("test_select_hash_key")
+	if _, err := db.HSet(key, []byte("a"), value); err != nil {
+		t.Fatal(err)
+	}
+
+	if v, err := db.HGet(key, []byte("a")); err != nil {
+		t.Fatal(err)
+	} else if string(v) != string(value) {
+		t.Fatal(string(v))
+	}
+
+	key = []byte("test_select_set_key")
+	if _, err := db.SAdd(key, []byte("a"), []byte("b")); err != nil {
+		t.Fatal(err)
+	}
+
+	if n, err := db.SIsMember(key, []byte("a")); err != nil {
+		t.Fatal(err)
+	} else if n != 1 {
+		t.Fatal(n)
+	}
+
+	key = []byte("test_select_zset_key")
+	if _, err := db.ZAdd(key, ScorePair{1, []byte("a")}, ScorePair{2, []byte("b")}); err != nil {
+		t.Fatal(err)
+	}
+
+	if v, err := db.ZRangeByScore(key, 0, 100, 0, -1); err != nil {
+		t.Fatal(err)
+	} else if len(v) != 2 {
+		t.Fatal(len(v))
+	}
 }
 
 func TestFlush(t *testing.T) {
diff --git a/ledis/scan.go b/ledis/scan.go
index cdf18dc..94bff5d 100644
--- a/ledis/scan.go
+++ b/ledis/scan.go
@@ -178,11 +178,22 @@ func (db *DB) encodeScanKey(storeDataType byte, key []byte) ([]byte, error) {
 	}
 }
 
-func (db *DB) decodeScanKey(storeDataType byte, ek []byte) ([]byte, error) {
-	if len(ek) < 2 || ek[0] != db.index || ek[1] != storeDataType {
-		return nil, errMetaKey
+func (db *DB) decodeScanKey(storeDataType byte, ek []byte) (key []byte, err error) {
+	switch storeDataType {
+	case KVType:
+		key, err = db.decodeKVKey(ek)
+	case LMetaType:
+		key, err = db.lDecodeMetaKey(ek)
+	case HSizeType:
+		key, err = db.hDecodeSizeKey(ek)
+	case ZSizeType:
+		key, err = db.zDecodeSizeKey(ek)
+	case SSizeType:
+		key, err = db.sDecodeSizeKey(ek)
+	default:
+		err = errDataType
 	}
-	return ek[2:], nil
+	return
 }
 
 // for specail data scan
diff --git a/ledis/t_hash.go b/ledis/t_hash.go
index cd158cb..9914ea8 100644
--- a/ledis/t_hash.go
+++ b/ledis/t_hash.go
@@ -31,29 +31,41 @@ func checkHashKFSize(key []byte, field []byte) error {
 }
 
 func (db *DB) hEncodeSizeKey(key []byte) []byte {
-	buf := make([]byte, len(key)+2)
+	buf := make([]byte, len(key)+1+len(db.indexVarBuf))
 
-	buf[0] = db.index
-	buf[1] = HSizeType
+	pos := 0
+	n := copy(buf, db.indexVarBuf)
+
+	pos += n
+	buf[pos] = HSizeType
+
+	pos++
+	copy(buf[pos:], key)
 
-	copy(buf[2:], key)
 	return buf
 }
 
 func (db *DB) hDecodeSizeKey(ek []byte) ([]byte, error) {
-	if len(ek) < 2 || ek[0] != db.index || ek[1] != HSizeType {
-		return nil, errHSizeKey
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, err
 	}
 
-	return ek[2:], nil
+	if pos+1 > len(ek) || ek[pos] != HSizeType {
+		return nil, errHSizeKey
+	}
+	pos++
+
+	return ek[pos:], nil
 }
 
 func (db *DB) hEncodeHashKey(key []byte, field []byte) []byte {
-	buf := make([]byte, len(key)+len(field)+1+1+2+1)
+	buf := make([]byte, len(key)+len(field)+1+1+2+len(db.indexVarBuf))
 
 	pos := 0
-	buf[pos] = db.index
-	pos++
+	n := copy(buf, db.indexVarBuf)
+	pos += n
+
 	buf[pos] = HashType
 	pos++
 
@@ -71,15 +83,24 @@ func (db *DB) hEncodeHashKey(key []byte, field []byte) []byte {
 }
 
 func (db *DB) hDecodeHashKey(ek []byte) ([]byte, []byte, error) {
-	if len(ek) < 5 || ek[0] != db.index || ek[1] != HashType {
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if pos+1 > len(ek) || ek[pos] != HashType {
+		return nil, nil, errHashKey
+	}
+	pos++
+
+	if pos+2 > len(ek) {
 		return nil, nil, errHashKey
 	}
 
-	pos := 2
 	keyLen := int(binary.BigEndian.Uint16(ek[pos:]))
 	pos += 2
 
-	if keyLen+5 > len(ek) {
+	if keyLen+pos > len(ek) {
 		return nil, nil, errHashKey
 	}
 
diff --git a/ledis/t_kv.go b/ledis/t_kv.go
index eb2f1fe..8c85c52 100644
--- a/ledis/t_kv.go
+++ b/ledis/t_kv.go
@@ -33,19 +33,26 @@ func checkValueSize(value []byte) error {
 }
 
 func (db *DB) encodeKVKey(key []byte) []byte {
-	ek := make([]byte, len(key)+2)
-	ek[0] = db.index
-	ek[1] = KVType
-	copy(ek[2:], key)
+	ek := make([]byte, len(key)+1+len(db.indexVarBuf))
+	pos := copy(ek, db.indexVarBuf)
+	ek[pos] = KVType
+	pos++
+	copy(ek[pos:], key)
 	return ek
 }
 
 func (db *DB) decodeKVKey(ek []byte) ([]byte, error) {
-	if len(ek) < 2 || ek[0] != db.index || ek[1] != KVType {
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, err
+	}
+	if pos+1 > len(ek) || ek[pos] != KVType {
 		return nil, errKVKey
 	}
 
-	return ek[2:], nil
+	pos++
+
+	return ek[pos:], nil
 }
 
 func (db *DB) encodeKVMinKey() []byte {
diff --git a/ledis/t_list.go b/ledis/t_list.go
index ce6eeb0..c872c7b 100644
--- a/ledis/t_list.go
+++ b/ledis/t_list.go
@@ -24,28 +24,34 @@ var errListKey = errors.New("invalid list key")
 var errListSeq = errors.New("invalid list sequence, overflow")
 
 func (db *DB) lEncodeMetaKey(key []byte) []byte {
-	buf := make([]byte, len(key)+2)
-	buf[0] = db.index
-	buf[1] = LMetaType
+	buf := make([]byte, len(key)+1+len(db.indexVarBuf))
+	pos := copy(buf, db.indexVarBuf)
+	buf[pos] = LMetaType
+	pos++
 
-	copy(buf[2:], key)
+	copy(buf[pos:], key)
 	return buf
 }
 
 func (db *DB) lDecodeMetaKey(ek []byte) ([]byte, error) {
-	if len(ek) < 2 || ek[0] != db.index || ek[1] != LMetaType {
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, err
+	}
+
+	if pos+1 > len(ek) || ek[pos] != LMetaType {
 		return nil, errLMetaKey
 	}
 
-	return ek[2:], nil
+	pos++
+	return ek[pos:], nil
 }
 
 func (db *DB) lEncodeListKey(key []byte, seq int32) []byte {
-	buf := make([]byte, len(key)+8)
+	buf := make([]byte, len(key)+7+len(db.indexVarBuf))
+
+	pos := copy(buf, db.indexVarBuf)
 
-	pos := 0
-	buf[pos] = db.index
-	pos++
 	buf[pos] = ListType
 	pos++
 
@@ -61,19 +67,33 @@ func (db *DB) lEncodeListKey(key []byte, seq int32) []byte {
 }
 
 func (db *DB) lDecodeListKey(ek []byte) (key []byte, seq int32, err error) {
-	if len(ek) < 8 || ek[0] != db.index || ek[1] != ListType {
+	pos := 0
+	pos, err = db.checkKeyIndex(ek)
+	if err != nil {
+		return
+	}
+
+	if pos+1 > len(ek) || ek[pos] != ListType {
 		err = errListKey
 		return
 	}
 
-	keyLen := int(binary.BigEndian.Uint16(ek[2:]))
-	if keyLen+8 != len(ek) {
+	pos++
+
+	if pos+2 > len(ek) {
 		err = errListKey
 		return
 	}
 
-	key = ek[4 : 4+keyLen]
-	seq = int32(binary.BigEndian.Uint32(ek[4+keyLen:]))
+	keyLen := int(binary.BigEndian.Uint16(ek[pos:]))
+	pos += 2
+	if keyLen+pos+4 != len(ek) {
+		err = errListKey
+		return
+	}
+
+	key = ek[pos : pos+keyLen]
+	seq = int32(binary.BigEndian.Uint32(ek[pos+keyLen:]))
 	return
 }
 
diff --git a/ledis/t_set.go b/ledis/t_set.go
index 3980768..998170a 100644
--- a/ledis/t_set.go
+++ b/ledis/t_set.go
@@ -29,29 +29,36 @@ func checkSetKMSize(key []byte, member []byte) error {
 }
 
 func (db *DB) sEncodeSizeKey(key []byte) []byte {
-	buf := make([]byte, len(key)+2)
+	buf := make([]byte, len(key)+1+len(db.indexVarBuf))
 
-	buf[0] = db.index
-	buf[1] = SSizeType
+	pos := copy(buf, db.indexVarBuf)
+	buf[pos] = SSizeType
 
-	copy(buf[2:], key)
+	pos++
+
+	copy(buf[pos:], key)
 	return buf
 }
 
 func (db *DB) sDecodeSizeKey(ek []byte) ([]byte, error) {
-	if len(ek) < 2 || ek[0] != db.index || ek[1] != SSizeType {
-		return nil, errSSizeKey
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, err
 	}
 
-	return ek[2:], nil
+	if pos+1 > len(ek) || ek[pos] != SSizeType {
+		return nil, errSSizeKey
+	}
+	pos++
+
+	return ek[pos:], nil
 }
 
 func (db *DB) sEncodeSetKey(key []byte, member []byte) []byte {
-	buf := make([]byte, len(key)+len(member)+1+1+2+1)
+	buf := make([]byte, len(key)+len(member)+1+1+2+len(db.indexVarBuf))
+
+	pos := copy(buf, db.indexVarBuf)
 
-	pos := 0
-	buf[pos] = db.index
-	pos++
 	buf[pos] = SetType
 	pos++
 
@@ -69,15 +76,25 @@ func (db *DB) sEncodeSetKey(key []byte, member []byte) []byte {
 }
 
 func (db *DB) sDecodeSetKey(ek []byte) ([]byte, []byte, error) {
-	if len(ek) < 5 || ek[0] != db.index || ek[1] != SetType {
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if pos+1 > len(ek) || ek[pos] != SetType {
+		return nil, nil, errSetKey
+	}
+
+	pos++
+
+	if pos+2 > len(ek) {
 		return nil, nil, errSetKey
 	}
 
-	pos := 2
 	keyLen := int(binary.BigEndian.Uint16(ek[pos:]))
 	pos += 2
 
-	if keyLen+5 > len(ek) {
+	if keyLen+pos > len(ek) {
 		return nil, nil, errSetKey
 	}
 
diff --git a/ledis/t_ttl.go b/ledis/t_ttl.go
index 7758fc8..2785a1d 100644
--- a/ledis/t_ttl.go
+++ b/ledis/t_ttl.go
@@ -28,11 +28,12 @@ type ttlChecker struct {
 var errExpType = errors.New("invalid expire type")
 
 func (db *DB) expEncodeTimeKey(dataType byte, key []byte, when int64) []byte {
-	buf := make([]byte, len(key)+11)
+	buf := make([]byte, len(key)+10+len(db.indexVarBuf))
 
-	buf[0] = db.index
-	buf[1] = ExpTimeType
-	pos := 2
+	pos := copy(buf, db.indexVarBuf)
+
+	buf[pos] = ExpTimeType
+	pos++
 
 	binary.BigEndian.PutUint64(buf[pos:], uint64(when))
 	pos += 8
@@ -46,12 +47,13 @@ func (db *DB) expEncodeTimeKey(dataType byte, key []byte, when int64) []byte {
 }
 
 func (db *DB) expEncodeMetaKey(dataType byte, key []byte) []byte {
-	buf := make([]byte, len(key)+3)
+	buf := make([]byte, len(key)+2+len(db.indexVarBuf))
 
-	buf[0] = db.index
-	buf[1] = ExpMetaType
-	buf[2] = dataType
-	pos := 3
+	pos := copy(buf, db.indexVarBuf)
+	buf[pos] = ExpMetaType
+	pos++
+	buf[pos] = dataType
+	pos++
 
 	copy(buf[pos:], key)
 
@@ -59,19 +61,29 @@ func (db *DB) expEncodeMetaKey(dataType byte, key []byte) []byte {
 }
 
 func (db *DB) expDecodeMetaKey(mk []byte) (byte, []byte, error) {
-	if len(mk) <= 3 || mk[0] != db.index || mk[1] != ExpMetaType {
+	pos, err := db.checkKeyIndex(mk)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	if pos+2 > len(mk) || mk[pos] != ExpMetaType {
 		return 0, nil, errExpMetaKey
 	}
 
-	return mk[2], mk[3:], nil
+	return mk[pos+1], mk[pos+2:], nil
 }
 
 func (db *DB) expDecodeTimeKey(tk []byte) (byte, []byte, int64, error) {
-	if len(tk) < 11 || tk[0] != db.index || tk[1] != ExpTimeType {
+	pos, err := db.checkKeyIndex(tk)
+	if err != nil {
+		return 0, nil, 0, err
+	}
+
+	if pos+10 > len(tk) || tk[pos] != ExpTimeType {
 		return 0, nil, 0, errExpTimeKey
 	}
 
-	return tk[10], tk[11:], int64(binary.BigEndian.Uint64(tk[2:])), nil
+	return tk[pos+9], tk[pos+10:], int64(binary.BigEndian.Uint64(tk[pos+1:])), nil
 }
 
 func (db *DB) expire(t *batch, dataType byte, key []byte, duration int64) {
diff --git a/ledis/t_ttl_test.go b/ledis/t_ttl_test.go
index 371a40d..f261399 100644
--- a/ledis/t_ttl_test.go
+++ b/ledis/t_ttl_test.go
@@ -437,3 +437,31 @@ func TestExpCompose(t *testing.T) {
 
 	return
 }
+
+func TestTTLCodec(t *testing.T) {
+	db := getTestDB()
+
+	key := []byte("key")
+	ek := db.expEncodeTimeKey(KVType, key, 10)
+
+	if tp, k, when, err := db.expDecodeTimeKey(ek); err != nil {
+		t.Fatal(err)
+	} else if tp != KVType {
+		t.Fatal(tp, KVType)
+	} else if string(k) != "key" {
+		t.Fatal(string(k))
+	} else if when != 10 {
+		t.Fatal(when)
+	}
+
+	ek = db.expEncodeMetaKey(KVType, key)
+
+	if tp, k, err := db.expDecodeMetaKey(ek); err != nil {
+		t.Fatal(err)
+	} else if tp != KVType {
+		t.Fatal(tp, KVType)
+	} else if string(k) != "key" {
+		t.Fatal(string(k))
+	}
+
+}
diff --git a/ledis/t_zset.go b/ledis/t_zset.go
index e33344a..6b65f4d 100644
--- a/ledis/t_zset.go
+++ b/ledis/t_zset.go
@@ -51,28 +51,31 @@ func checkZSetKMSize(key []byte, member []byte) error {
 }
 
 func (db *DB) zEncodeSizeKey(key []byte) []byte {
-	buf := make([]byte, len(key)+2)
-	buf[0] = db.index
-	buf[1] = ZSizeType
-
-	copy(buf[2:], key)
+	buf := make([]byte, len(key)+1+len(db.indexVarBuf))
+	pos := copy(buf, db.indexVarBuf)
+	buf[pos] = ZSizeType
+	pos++
+	copy(buf[pos:], key)
 	return buf
 }
 
 func (db *DB) zDecodeSizeKey(ek []byte) ([]byte, error) {
-	if len(ek) < 2 || ek[0] != db.index || ek[1] != ZSizeType {
-		return nil, errZSizeKey
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, err
 	}
 
-	return ek[2:], nil
+	if pos+1 > len(ek) || ek[pos] != ZSizeType {
+		return nil, errZSizeKey
+	}
+	pos++
+	return ek[pos:], nil
 }
 
 func (db *DB) zEncodeSetKey(key []byte, member []byte) []byte {
-	buf := make([]byte, len(key)+len(member)+5)
+	buf := make([]byte, len(key)+len(member)+4+len(db.indexVarBuf))
 
-	pos := 0
-	buf[pos] = db.index
-	pos++
+	pos := copy(buf, db.indexVarBuf)
 
 	buf[pos] = ZSetType
 	pos++
@@ -92,22 +95,35 @@ func (db *DB) zEncodeSetKey(key []byte, member []byte) []byte {
 }
 
 func (db *DB) zDecodeSetKey(ek []byte) ([]byte, []byte, error) {
-	if len(ek) < 5 || ek[0] != db.index || ek[1] != ZSetType {
+	pos, err := db.checkKeyIndex(ek)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if pos+1 > len(ek) || ek[pos] != ZSetType {
 		return nil, nil, errZSetKey
 	}
 
-	keyLen := int(binary.BigEndian.Uint16(ek[2:]))
-	if keyLen+5 > len(ek) {
+	pos++
+
+	if pos+2 > len(ek) {
 		return nil, nil, errZSetKey
 	}
 
-	key := ek[4 : 4+keyLen]
-
-	if ek[4+keyLen] != zsetStartMemSep {
+	keyLen := int(binary.BigEndian.Uint16(ek[pos:]))
+	if keyLen+pos > len(ek) {
 		return nil, nil, errZSetKey
 	}
 
-	member := ek[5+keyLen:]
+	pos += 2
+	key := ek[pos : pos+keyLen]
+
+	if ek[pos+keyLen] != zsetStartMemSep {
+		return nil, nil, errZSetKey
+	}
+	pos++
+
+	member := ek[pos+keyLen:]
 	return key, member, nil
 }
 
@@ -123,11 +139,9 @@ func (db *DB) zEncodeStopSetKey(key []byte) []byte {
 }
 
 func (db *DB) zEncodeScoreKey(key []byte, member []byte, score int64) []byte {
-	buf := make([]byte, len(key)+len(member)+14)
+	buf := make([]byte, len(key)+len(member)+13+len(db.indexVarBuf))
 
-	pos := 0
-	buf[pos] = db.index
-	pos++
+	pos := copy(buf, db.indexVarBuf)
 
 	buf[pos] = ZScoreType
 	pos++
@@ -166,20 +180,38 @@ func (db *DB) zEncodeStopScoreKey(key []byte, score int64) []byte {
 }
 
 func (db *DB) zDecodeScoreKey(ek []byte) (key []byte, member []byte, score int64, err error) {
-	if len(ek) < 14 || ek[0] != db.index || ek[1] != ZScoreType {
+	pos := 0
+	pos, err = db.checkKeyIndex(ek)
+	if err != nil {
+		return
+	}
+
+	if pos+1 > len(ek) || ek[pos] != ZScoreType {
+		err = errZScoreKey
+		return
+	}
+	pos++
+
+	if pos+2 > len(ek) {
+		err = errZScoreKey
+		return
+	}
+	keyLen := int(binary.BigEndian.Uint16(ek[pos:]))
+	pos += 2
+
+	if keyLen+pos > len(ek) {
 		err = errZScoreKey
 		return
 	}
 
-	keyLen := int(binary.BigEndian.Uint16(ek[2:]))
-	if keyLen+14 > len(ek) {
+	key = ek[pos : pos+keyLen]
+	pos += keyLen
+
+	if pos+10 > len(ek) {
 		err = errZScoreKey
 		return
 	}
 
-	key = ek[4 : 4+keyLen]
-	pos := 4 + keyLen
-
 	if (ek[pos] != zsetNScoreSep) && (ek[pos] != zsetPScoreSep) {
 		err = errZScoreKey
 		return