On 22/10/13 09:01, Tom Lane wrote:
Gavin Flower <gavinflo...@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
Yeah, obvious - in retrospect! :-)
One way it could be done, but even this would consume far too much
storage and processing power (hence totally impractical), would be to
'simply' store a counter for each value found and increment it for each
occurence...
Cheers,
Gavin
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