private void resetVectorizedRowBatchForDeserialize() {
    /**
     * Reset existing input columns
     */
    for (int c = 0; c < currentDataColumnCount; c++) {
      resetColumnVector(deserializerBatch.cols[c]);
    }

    /**
     * Reset output and scratch columns
     */
    for (int c = dataColumnCount + partitionColumnCount; c < deserializerBatch.cols.length; c++) {
      if (c == rowIdentifierColumnNum) {
        continue;
      }
      resetColumnVector(deserializerBatch.cols[c]);
    }
    deserializerBatch.selectedInUse = false;
    deserializerBatch.size = 0;
    deserializerBatch.endOfFile = false;
  }
Reset all the columns excluding
- partition columns because they are read only once per file during first batch read
- any columns that defaulted to NULL because they are not present in this partition

See {@link #setupPartitionContextVars(Path)}
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorMapOperator.java