presto-main/src/main/java/io/prestosql/split/SampledSplitSource.java/SampledSplitSource/SampledSplitSource
class SampledSplitSource:    public SampledSplitSource(SplitSource splitSource, double sampleRatio)
    {
        this.splitSource = requireNonNull(splitSource, "dataSource is null");
        this.sampleRatio = sampleRatio;
    }