stats_collector.awk

function step_std_dev(val) {
    n += 1
    delta = val - mean
    mean = mean + delta/n
    M2 = M2 + delta*(val - mean)  # This expression uses the new value of mean
    if (n > 1) {
	variance_n = M2/n
	variance = M2/(n - 1)
    }
}

BEGIN {
    sum = 0
    max = 0
    count = 0
    min = 1000000000000000
    n = 0
    mean = 0
    M2 = 0
}

{ requests += 1 }
{ sum += $2 }
{ step_std_dev($2) }
{ if ($1 > max) max = $1 }
{ if ($1 < min) min = $1 }

END {
    seconds = (max - min) / 1000
    printf( "requests: %d\n sum: %d\n elapsed time: %d seconds\n rate: %f req/s\n mean: %f\n stddev: %f\n\n",
	    requests, sum, seconds, requests / seconds, mean, sqrt(variance))
}