code: func (t *tableCommon) WritableIndices() []table.Index {
  	if len(t.writableIndices) > 0 {
  		return t.writableIndices
  	}
  	writable := make([]table.Index, 0, len(t.indices))
  	for _, index := range t.indices {
  		s := index.Meta().State
  		if s != model.StateDeleteOnly && s != model.StateDeleteReorganization {
  			writable = append(writable, index)
  		}
  	}
  	return writable
  }
docs: // WritableIndices implements table.Table WritableIndices interface.