Re: Merge algorithms for large numbers of "tapes" - Mailing list pgsql-hackers

From Jim C. Nasby
Subject Re: Merge algorithms for large numbers of "tapes"
Date
Msg-id 20060309163552.GD45250@pervasive.com
Whole thread Raw
In response to Re: Merge algorithms for large numbers of "tapes"  (Greg Stark <gsstark@mit.edu>)
Responses Re: Merge algorithms for large numbers of "tapes"
List pgsql-hackers
On Wed, Mar 08, 2006 at 10:20:08PM -0500, Greg Stark wrote:
> > For that to be of any use, wouldn't you need to use only as many tapes
> > as spindles/2? Otherwise you're still trying to read and write from the
> > same set of drives, which means you're probably doing a lot of seeking.
> > Or do the tape algorithms re-write data as they read it?
> 
> Well, spindles-1. I was thinking as many tapes as you have spindles *in total*,
> ie, including the output tape. You only have one output tape for each n-way
> merge though.

Well, the reality remains though; most folks are unlikely to setup
enough dedicated temp areas so that we can do one tape per disk, so it
would be really good to have a sort method that didn't rely on that.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461


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