Re: [HACKERS] sorting big tables :( - Mailing list pgsql-hackers

From Eivind Eklund
Subject Re: [HACKERS] sorting big tables :(
Date
Msg-id 19980520224430.04725@follo.net
Whole thread Raw
In response to Re: [HACKERS] sorting big tables :(  (The Hermit Hacker <scrappy@hub.org>)
List pgsql-hackers
On Wed, May 20, 1998 at 01:17:34PM -0400, The Hermit Hacker wrote:
> On Wed, 20 May 1998, Tom wrote:
> >   No, that doesn't happen.  The only way to eliminate fragmentation is a
> > dump/newfs/restore cycle.  UFS does do fragmentation avoidance (which is
> > reason UFS filesystems have a 10% reserve).
>
>     Okay, then we have two different understandings of this.  My
> understanding was that the 10% reserve gave the OS a 'temp area' in which
> to move blocks to/from so that it could defrag on the fly...

No.  What is done is (quite correctly) fragmentation avoidance.  Big
files are even sometimes fragmented on purpose, to allow small files
that are written later to avoid being fragmented.

Eivind.

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