RE: Datafile size - Is bigger better?

  • From: "Baumgartel, Paul" <paul.baumgartel@xxxxxxxxxxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Wed, 15 Nov 2006 18:39:13 -0000

I usually add 1MB to all file sizes, just to make the math and the filesize 
specification simpler--if I want 1024MB of space, I make the file 1025MB.

Paul Baumgartel 
Information Technology 
DBA & Admin - NY, KIGA 1 
11 Madison Avenue 
New York, NY 10010 
Phone 212.538.1143 

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On 
Behalf Of Wolfgang Breitling
Sent: Tuesday, November 14, 2006 11:40 PM
To: jaykash@xxxxxxxxxxx
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: Datafile size - Is bigger better?

At 07:09 PM 11/14/2006, Wolfgang Breitling wrote:

At 03:57 PM 11/14/2006, JayDBA wrote:

3. On locally managed files, we loose header space equal to the extent size. 
E.g. on a datafile with uniform extent sizing of 128M a 2gb file would waste 6% 
space / file. This number can run into gigabytes on systems with 100's of 
1000's of files

That is not true. The bitmap(s) for managing the space are fixed at 64K. If you 
create the datafiles for LMTs as an integral multiple of the uniform extent 
size + 64K, you can use the full size of the tablespace. If not Oracle will 
take the first extent and use 64K of it for the bitmap but the remainder is not 
usable - until you extent the datafile size by 64K:

I was describing that wrong. Oracle is not taking the first extent to create 
the space bitmap. It takes the first 64K of the datafile - after the file 
header block - to create the bitmap. The first extent then starts at an offset 
of 64K + 1 block. But if the datafile size does not include the extra 64K for 
the bitmap the space left after the last uniform size extent is allocated is 
64K short of a full extent and is therefore unusable. Once the additional 64K 
are added, that unusable space plus the 64K make for a full uniform size extent 
and can be used.


Wolfgang Breitling
Centrex Consulting Corporation <>  

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