code: func (c *Chunk) Reset() {
  	if c.columns == nil {
  		return
  	}
  	for _, col := range c.columns {
  		col.reset()
  	}
  	c.numVirtualRows = 0
  }
docs: // Reset resets the chunk, so the memory it allocated can be reused.
  // Make sure all the data in the chunk is not used anymore before you reuse this chunk.