db.go
func (db *DB) Size() (lsm, vlog int64) {
	if y.LSMSize.Get(db.opt.Dir) == nil {
		lsm, vlog = 0, 0
		return
	}
	lsm = y.LSMSize.Get(db.opt.Dir).(*expvar.Int).Value()
	vlog = y.VlogSize.Get(db.opt.Dir).(*expvar.Int).Value()
	return
}
func (db *DB) Size() (lsm, vlog int64) {
	if y.LSMSize.Get(db.opt.Dir) == nil {
		lsm, vlog = 0, 0
		return
	}
	lsm = y.LSMSize.Get(db.opt.Dir).(*expvar.Int).Value()
	vlog = y.VlogSize.Get(db.opt.Dir).(*expvar.Int).Value()
	return
}
// Size returns the size of lsm and value log files in bytes. It can be used to decide how often to
// call RunValueLogGC.