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Re: [PERFORM] Releasing memory during External sorting?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Ron Peacetree <rjpeace(at)earthlink(dot)net>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>,pgsql-hackers(at)postgresql(dot)org, pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] Releasing memory during External sorting?
Date: 2005-09-23 17:17:24
Message-ID: 5021.1127495844@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
Ron Peacetree <rjpeace(at)earthlink(dot)net> writes:
> 2= No optimal external sorting algorithm should use more than 2 passes.
> 3= Optimal external sorting algorithms should use 1 pass if at all possible.

A comparison-based sort must use at least N log N operations, so it
would appear to me that if you haven't got approximately log N passes
then your algorithm doesn't work.

			regards, tom lane

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