presto-main/src/main/java/io/prestosql/sql/analyzer/Analysis.java/Analysis/getSampleRatio
class Analysis:    public double getSampleRatio(SampledRelation relation)
    {
        NodeRef<SampledRelation> key = NodeRef.of(relation);
        checkState(sampleRatios.containsKey(key), "Sample ratio missing for %s. Broken analysis?", relation);
        return sampleRatios.get(key);
    }