I'm already using the accumulator below to keep track of request processing times of a server.

    using ProcAcc = acc::accumulator_set<
        double, acc::stats<
            acc::tag::min,
            acc::tag::max,
            acc::tag::mean,
            acc::tag::median,
            acc::tag::sum
        >
    >;

But now I'm interested in also extracting the P90 and P99 values,

to get insight in how much of an outlier the max could be.

AFAIK, the median is the P50, but it's not readily obvious to me what tag

to use for the P90 or P(N) in general. Could someone help please? Thanks, --DD

PS: Does accumulator allow to keep the top(N) values as well? How?

  https://www.boost.org/doc/libs/1_75_0/doc/html/accumulators/user_s_guide.html#accumulators.user_s_guide.the_statistical_accumulators_library.extended_p_square

  https://www.boost.org/doc/libs/1_75_0/doc/html/accumulators/user_s_guide.html#accumulators.user_s_guide.the_statistical_accumulators_library.extended_p_square_quantile

In particular, to compute both P90 and P99, together with min, max, mean, ..., just add the "extended_p_square" tag (or the "extended_p_square_quantile" tag) and specify probabilities 0.90 and 0.99 in the constructor:

    typedef accumulator_set<double,
                                             stats<tag::extended_p_square,

                                                       tag::max,
                                                       tag::mean,
                                                       tag::median,
                                                       tag::sum
                                                    >
                                           > acc_t;

    double probs[] = {0.90, 0.99);

    acc_t acc(extended_p_square_probabilities = probs);

    acc(value1);

    ...

    std::cout << "Min: " << min(acc) << "\n";
    std::cout << "Max: " << max(acc) << "\n";
    std::cout << "Mean: " << mean(acc) << "\n";
    std::cout << "Median: " << median(acc) << "\n";
    std::cout << "Sum: " << sum(acc) << "\n";

Hope this helps.

Regards,

Marco