-Original Message-
From: Ron Peacetree [mailto:[EMAIL PROTECTED]
Sent: Saturday, September 24, 2005 3:31 AM
To: Dann Corbit; pgsql-hackers@postgresql.org; pgsql-
[EMAIL PROTECTED]
Subject: RE: [HACKERS] [PERFORM] Releasing memory during External
sorting?
From: Dann Corbit [EMAIL
On Fri, 2005-09-23 at 12:48 -0400, Ron Peacetree wrote:
I have some indications from private tests that very high memory settings
may actually hinder performance of the sorts, though I cannot explain that
and wonder whether it is the performance tests themselves that have issues.
Hmmm.
From: Dann Corbit [EMAIL PROTECTED]
Sent: Sep 23, 2005 5:38 PM
Subject: RE: [HACKERS] [PERFORM] Releasing memory during External sorting?
_C Unleashed_ also explains how to use a callback function to perform
arbitrary radix sorts (you simply need a method that returns the
[bucketsize] most
From: Tom Lane [EMAIL PROTECTED]
Sent: Sep 23, 2005 2:15 PM
Subject: Re: [PERFORM] Releasing memory during External sorting?
Mark Lewis [EMAIL PROTECTED] writes:
operations != passes. If you were clever, you could probably write a
modified bubble-sort algorithm that only made 2 passes. A
From: Simon Riggs [EMAIL PROTECTED]
Sent: Sep 23, 2005 5:37 AM
Subject: [PERFORM] Releasing memory during External sorting?
I have concerns about whether we are overallocating memory for use in
external sorts. (All code relating to this is in tuplesort.c)
A decent external sorting algorithm, say
Yep. Also, bear in mind that the lg(n!)= ~ nlgn - n lower bound on
the number of comparisions:
a= says nothing about the amount of data movement used.
b= only holds for generic comparison based sorting algorithms.
As Knuth says (vol 3, p180), Distribution Counting sorts without
ever comparing
operations != passes. If you were clever, you could probably write a
modified bubble-sort algorithm that only made 2 passes. A pass is a
disk scan, operations are then performed (hopefully in memory) on what
you read from the disk. So there's no theoretical log N lower-bound on
the number of
-
From: [EMAIL PROTECTED] [mailto:pgsql-hackers-
[EMAIL PROTECTED] On Behalf Of Ron Peacetree
Sent: Friday, September 23, 2005 11:41 AM
To: Mark Lewis; Tom Lane; pgsql-hackers@postgresql.org; pgsql-
[EMAIL PROTECTED]
Subject: Re: [HACKERS] [PERFORM] Releasing memory during External
sorting?
Yep
Ron Peacetree [EMAIL PROTECTED] 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
Mark Lewis [EMAIL PROTECTED] writes:
operations != passes. If you were clever, you could probably write a
modified bubble-sort algorithm that only made 2 passes. A pass is a
disk scan, operations are then performed (hopefully in memory) on what
you read from the disk. So there's no
PROTECTED] On Behalf Of Dann Corbit
Sent: Friday, September 23, 2005 2:21 PM
To: Ron Peacetree; Mark Lewis; Tom Lane; pgsql-hackers@postgresql.org;
pgsql-performance@postgresql.org
Subject: Re: [HACKERS] [PERFORM] Releasing memory during External
sorting?
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