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Re: wip: functions median and percentile

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, David Fetter <david(at)fetter(dot)org>
Subject: Re: wip: functions median and percentile
Date: 2010-08-19 16:49:45
Message-ID: AANLkTi=yam_+-6vMeJVEyutBa3wizxSph0EE2PHddkK2@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-rrreviewers
On Thu, Aug 19, 2010 at 11:33 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Greg Stark <gsstark(at)mit(dot)edu> writes:
>> On Thu, Aug 19, 2010 at 11:59 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
>>> I am sending a prototype implementation of functions median and
>>> percentile. This implementation is very simple and I moved it to
>>> contrib for this moment - it is more easy maintainable. Later I'll
>>> move it to core.
>
>> So if the entire result set fits in memory it would be nice to use the
>> O(n) Quickselect algorithm -- which would only be a small change to
>> the existing Quicksort code -- instead of sorting the entire set.
>
> That seems like rather a lot of added infrastructure for functions whose
> popularity is at best unknown.  I think we should KISS for the first
> implementation.

+1.  I think the functions are useful, but the perfect is the enemy of the good.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company

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