presto-main/src/main/java/io/prestosql/operator/TableWriterOperator.java/TableWriterOperator/createStatisticsPage
class TableWriterOperator:    private Page createStatisticsPage(Page aggregationOutput)
    {
        int positionCount = aggregationOutput.getPositionCount();
        Block[] outputBlocks = new Block[types.size()];
        for (int channel = 0; channel < types.size(); channel++) {
            if (channel < STATS_START_CHANNEL) {
                outputBlocks[channel] = RunLengthEncodedBlock.create(types.get(channel), null, positionCount);
            }
            else {
                outputBlocks[channel] = aggregationOutput.getBlock(channel - 2);
            }
        }
        return new Page(positionCount, outputBlocks);
    }