diff --git a/config/config.go b/config/config.go
index 7c1346b..61d4519 100644
--- a/config/config.go
+++ b/config/config.go
@@ -102,7 +102,7 @@ type Config struct {
 
 	DataDir string `toml:"data_dir"`
 
-	Databases uint8 `toml:"databases"`
+	Databases int `toml:"databases"`
 
 	DBName       string `toml:"db_name"`
 	DBPath       string `toml:"db_path"`
@@ -214,6 +214,10 @@ func (cfg *Config) adjust() {
 	cfg.ConnReadBufferSize = getDefault(4*KB, cfg.ConnReadBufferSize)
 	cfg.ConnWriteBufferSize = getDefault(4*KB, cfg.ConnWriteBufferSize)
 	cfg.TTLCheckInterval = getDefault(1, cfg.TTLCheckInterval)
+	cfg.Databases = getDefault(0, cfg.Databases)
+	if cfg.Databases > 256 {
+		cfg.Databases = 256
+	}
 }
 
 func (cfg *LevelDBConfig) adjust() {
diff --git a/etc/ledis.conf b/etc/ledis.conf
index bcc3820..9c34182 100644
--- a/etc/ledis.conf
+++ b/etc/ledis.conf
@@ -12,7 +12,7 @@ data_dir = "/tmp/ledis_server"
 # Set the number of databases. You can use `select dbindex` to choose a db.
 # dbindex must be in [0, databases - 1].
 # Maximum databases is 256. 
-databases = 16
+databases = 256
 
 # Log server command, set empty to disable
 access_log = ""
diff --git a/ledis/ledis.go b/ledis/ledis.go
index bda8f5a..c28c29b 100644
--- a/ledis/ledis.go
+++ b/ledis/ledis.go
@@ -45,6 +45,8 @@ func Open(cfg *config.Config) (*Ledis, error) {
 
 	if cfg.Databases == 0 {
 		cfg.Databases = 16
+	} else if cfg.Databases > 256 {
+		cfg.Databases = 256
 	}
 
 	os.MkdirAll(cfg.DataDir, 0755)
@@ -83,8 +85,8 @@ func Open(cfg *config.Config) (*Ledis, error) {
 	}
 
 	l.dbs = make([]*DB, cfg.Databases)
-	for i := uint8(0); i < cfg.Databases; i++ {
-		l.dbs[i] = l.newDB(i)
+	for i := 0; i < cfg.Databases; i++ {
+		l.dbs[i] = l.newDB(uint8(i))
 	}
 
 	l.checkTTL()
@@ -111,7 +113,7 @@ func (l *Ledis) Close() {
 
 func (l *Ledis) Select(index int) (*DB, error) {
 	if index < 0 || index >= len(l.dbs) {
-		return nil, fmt.Errorf("invalid db index %d", index)
+		return nil, fmt.Errorf("invalid db index %d, must in [0, %d]", index, len(l.dbs)-1)
 	}
 
 	return l.dbs[index], nil
diff --git a/server/cmd_server.go b/server/cmd_server.go
index b402fca..83f705c 100644
--- a/server/cmd_server.go
+++ b/server/cmd_server.go
@@ -121,7 +121,7 @@ func configGetCommand(c *client) error {
 	key := hack.String(args[1])
 	switch key {
 	case "databases":
-		ay = append(ay, []byte("databases"), num.FormatUint8ToSlice(c.app.cfg.Databases))
+		ay = append(ay, []byte("databases"), num.FormatIntToSlice(c.app.cfg.Databases))
 	}
 
 	c.resp.writeSliceArray(ay)
diff --git a/upgrade/ledis-upgrade-ttl/main.go b/upgrade/ledis-upgrade-ttl/main.go
index d7ddbed..b450b14 100644
--- a/upgrade/ledis-upgrade-ttl/main.go
+++ b/upgrade/ledis-upgrade-ttl/main.go
@@ -45,18 +45,18 @@ func main() {
 
 	wb := db.NewWriteBatch()
 
-	for i := uint8(0); i < cfg.Databases; i++ {
-		minK, maxK := oldKeyPair(i)
+	for i := 0; i < cfg.Databases; i++ {
+		minK, maxK := oldKeyPair(uint8(i))
 
 		it := db.RangeIterator(minK, maxK, store.RangeROpen)
 		num := 0
 		for ; it.Valid(); it.Next() {
-			dt, k, t, err := decodeOldKey(i, it.RawKey())
+			dt, k, t, err := decodeOldKey(uint8(i), it.RawKey())
 			if err != nil {
 				continue
 			}
 
-			newKey := encodeNewKey(i, dt, k, t)
+			newKey := encodeNewKey(uint8(i), dt, k, t)
 
 			wb.Put(newKey, it.RawValue())
 			wb.Delete(it.RawKey())