code: func NewMain() (*Main, error) {
  	return &Main{
  		Index:           "ssb",
  		ReadConcurrency: 1,
  		MapConcurrency:  4,
  		RecordBuf:       1000000,
  
  		nexter: pdk.NewNexter(),
  	}, nil
  }
docs: // NewMain crates a new Main with default values.