private void copyBufferedColumns(VectorizedRowBatch batch, VectorizedRowBatch bufferedBatch) {
    // Copy critical columns.
    final int size = batch.size;
    for (int i = 0; i < bufferedColumnMap.length; i++) {
      VectorizedBatchUtil.copyNonSelectedColumnVector(
          batch, bufferedColumnMap[i], bufferedBatch, i, size);
    }

    bufferedBatch.size = size;
  }
Jumps to a given block by index. This method doesn't take care of spilling the current contents
from memory (even if it would be needed), so it should be used in cases where the caller
already made sure the the current contents of bufferedBatches have been spilled, so this is a
private method intentionally.

@param toBlock
@throws HiveException
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/ptf/VectorPTFGroupBatches.java