presto-main/src/main/java/io/prestosql/operator/DeleteOperator.java/DeleteOperator/getOutput
class DeleteOperator:    @Override
    public Page getOutput()
    {
        if ((state != State.FINISHING) || !finishFuture.isDone()) {
            return null;
        }
        state = State.FINISHED;

        Collection<Slice> fragments = getFutureValue(finishFuture);

        // output page will only be constructed once,
        // so a new PageBuilder is constructed (instead of using PageBuilder.reset)
        PageBuilder page = new PageBuilder(fragments.size() + 1, TYPES);
        BlockBuilder rowsBuilder = page.getBlockBuilder(0);
        BlockBuilder fragmentBuilder = page.getBlockBuilder(1);

        // write row count
        page.declarePosition();
        BIGINT.writeLong(rowsBuilder, rowCount);
        fragmentBuilder.appendNull();

        // write fragments
        for (Slice fragment : fragments) {
            page.declarePosition();
            rowsBuilder.appendNull();
            VARBINARY.writeSlice(fragmentBuilder, fragment);
        }

        return page.build();
    }