code: func createTxidRangeStartKey(txid string) []byte {
  	var startKey []byte
  	startKey = append(startKey, prwsetPrefix)
  	startKey = append(startKey, compositeKeySep)
  	startKey = append(startKey, []byte(txid)...)
  	startKey = append(startKey, compositeKeySep)
  	return startKey
  }
docs: // createTxidRangeStartKey returns a startKey to do a range query on transient store using txid