Re: wip: functions median and percentile

Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com> writes:
> 2010/9/26 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:
>> This patch needs a few work - can share a compare functionality with
>> tuplesort.c, but I would to verify a concept now.

> Sorry for delay. I read the patch and it seems the result is sane. For
> window function calls, I agree that the current tuplesort is not
> enough to implement median functions and the patch introduces its own
> memsort mechanism, although memsort has too much copied from
> tuplesort. It looks to me not so difficult to modify the existing
> tuplesort to guarantee staying in memory always if an option to do so
> is specified from caller. I think that option can be used by other
> cases in the core code.

If this patch tries to force the entire sort to happen in memory,
it is not committable. What will happen when you get a lot of data?
You need to be working on a variant that will work anyway, not working
on an unacceptable lobotomization of the main sort code.

regards, tom lane