presto-main/src/main/java/io/prestosql/execution/QueryStats.java/QueryStats/getProgressPercentage
class QueryStats:    @JsonProperty
    public OptionalDouble getProgressPercentage()
    {
        if (!scheduled || totalDrivers == 0) {
            return OptionalDouble.empty();
        }
        return OptionalDouble.of(min(100, (completedDrivers * 100.0) / totalDrivers));
    }