我还没有找到一个计算处理的行数的步骤，但是您可以使用“用户定义的java类”步骤来计算行数并删除前4500行，代码如下：

// This will be the counter.
Long rowCount;

public boolean processRow(StepMetaInterface smi, StepDataInterface sdi) throws KettleException
{
    if (first) {
        rowCount = 0l;
        first=false;
    }

    Object[] r = getRow();
    if (r == null) {
        setOutputDone();
        return false;
    }

    // Increment of the counter.
    rowCount++;

    // Check ouf the counter. Doesn't output the current row if it's less than 4501.
    if (rowCount>4500l) {
        Object[] outputRow = createOutputRow(r, data.outputRowMeta.size());
        // Adds the row count to a stream field.
        get(Fields.Out, "Count").setValue(outputRow, rowCount);
        putRow(data.outputRowMeta, outputRow);
    }

    return true;
}

我用了下面的水壶文件，解决了我的问题。感谢@workinghard..和@jxc