presto-main/src/main/java/io/prestosql/cost/FilterStatsRule.java/FilterStatsRule/doCalculate
class FilterStatsRule:    @Override
    public Optional<PlanNodeStatsEstimate> doCalculate(FilterNode node, StatsProvider statsProvider, Lookup lookup, Session session, TypeProvider types)
    {
        PlanNodeStatsEstimate sourceStats = statsProvider.getStats(node.getSource());
        PlanNodeStatsEstimate estimate = filterStatsCalculator.filterStats(sourceStats, node.getPredicate(), session, types);
        if (isDefaultFilterFactorEnabled(session) && estimate.isOutputRowCountUnknown()) {
            estimate = sourceStats.mapOutputRowCount(sourceRowCount -> sourceStats.getOutputRowCount() * UNKNOWN_FILTER_COEFFICIENT);
        }
        return Optional.of(estimate);
    }