Quite difficult now to reach this scale with personnel records, but: imagine that you're asked to provide the median of one trillion data points. This could provide lots of interesting possible approaches, since it's about the boundary between "big data" vs "do it on your laptop". And you can't just load it into Excel.
For a trillion records, if you were in the UK government, you might just drop those above the Excel limit and proceed until journalists flagged the concern nationally.
(and also to ask about the range of the data!)