code: func searchIndex(names []string, index uint64) (int, bool) {
  	for i := len(names) - 1; i >= 0; i-- {
  		name := names[i]
  		_, curIndex, err := parseWalName(name)
  		if err != nil {
  			plog.Panicf("parse correct name should never fail: %v", err)
  		}
  		if index >= curIndex {
  			return i, true
  		}
  	}
  	return -1, false
  }
docs: // searchIndex returns the last array index of names whose raft index section is
  // equal to or smaller than the given index.
  // The given names MUST be sorted.