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Re: wip: functions median and percentile

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com>
Cc: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, David Fetter <david(at)fetter(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: wip: functions median and percentile
Date: 2010-10-01 13:05:43
Message-ID: 25774.1285938343@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-rrreviewers
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

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