In this case Tgres beats Whisper by quite a bit - it uses 8 bytes per data point. In fact looking at the numbers for a small test db I have 2,057,275 points taking up 16,687,104 bytes, which is exactly 8.11 bytes per point.

BTW getting the total point count is as easy as:

  select sum(array_length(dp,1)) from ts;

If you adjust the width (i.e. points per table row) to a higher number than the 768 default, as soon as you get above the PG pages size, TOAST (https://www.postgresql.org/docs/current/static/storage-toast...) kicks in, which PG compresses. Not sure how well this works, but at least in theory it should make it even more compact (though not sure about it being as performant).