code: func Renew(chk *Chunk, maxChunkSize int) *Chunk {
  	newChk := new(Chunk)
  	if chk.columns == nil {
  		return newChk
  	}
  	newCap := reCalcCapacity(chk, maxChunkSize)
  	newChk.columns = renewColumns(chk.columns, newCap)
  	newChk.numVirtualRows = 0
  	newChk.capacity = newCap
  	newChk.requiredRows = maxChunkSize
  	return newChk
  }
docs: // Renew creates a new Chunk based on an existing Chunk. The newly created Chunk
  // has the same data schema with the old Chunk. The capacity of the new Chunk
  // might be doubled based on the capacity of the old Chunk and the maxChunkSize.
  //  chk: old chunk(often used in previous call).
  //  maxChunkSize: the limit for the max number of rows.