Stats For Sysadmins

1/n chance tried n times

From https://theartofmachinery.com/2020/01/27/systems_programming_probability.html

For n>3, there's a bit less than a 2/3 chance of at least one hit.

n balls in n buckets

From https://theartofmachinery.com/2020/01/27/systems_programming_probability.html

If you throw n balls into n buckets at random, a bit over a third of the buckets will be empty, a bit over a third will have one ball, and the remaining quarter or so will have multiple balls.

Time to double

From https://web.stanford.edu/class/ee204/TheRuleof72.html

If you've got a thing growing a X% per day, it'll take 72/X days to double in size, roughly.

Scale up, or scale out?

From http://people.brunel.ac.uk/~mastjjb/jeb/or/queue.html

If you only care about throughput, scale up.

If you care about wait times, scale out.