Gavin Flower <GavinFlower@archidevsys.co.nz> writes:
>>> If we're going to extend pg_stat_statements, even more than min and max
>>> I'd like to see the standard deviation in execution time.
> How about the 'median', often a lot more useful than the 'arithmetic
> mean' (which most people call the 'average').
AFAIK, median is impossible to calculate cheaply (in particular, with
a fixed amount of workspace). So this apparently innocent request
is actually moving the goalposts a long way, because the space per
query table entry is a big concern for pg_stat_statements.
regards, tom lane