How to decrease memory usage when read orc file

[ggchangan]

I read an ORC file using code much like this:

	cursor := reader.Select(readColumns...)
	defer cursor.Close()
	err = cursor.PrepareStripe(sr.StripeObject.StripeIndex)
	for cursor.Next() {
		row0 := cursor.Row()
		row := make([]driver.Value, len(dataBlock.Columns.Columns))
		for i := range row0 {
			row[i] = driver.Value(row0[i])
		}
		for i, j := len(row0), 0; j < len(sr.StripeObject.ExtraValues); i, j = i+1, j+1 {
			row[i] = driver.Value(sr.StripeObject.ExtraValues[j])
		}
		dataBlock.Payload = append(dataBlock.Payload, row

I try to build a dataBlock with 20000 rows and then insert this dataBlock to ClickHouse, However this process consume too much memory. So is there any way which can be used to decrease memory usage when read orc file to build dataBlock?