Re: PCTFREE and PCTUSED

On the other hand, you might have overallocated the space, which would leave plenty of blocks on the free list, thus minimizing the impact. These things are best seen on "almost full" tables with things like row chaining, row migration, waits on ITL entries and other lovely things. Looks like you've benn lucky so far. As I've told you before, having tablespaces created with "SEGMENT SPACE MANAGEMENT AUTO" option takes care of that.
if your tablespace is created with a command like

"CREATE TABLESPACE DATA01
 DATAFILE '/data01/SID1/data01.dbf' size 8192M reuse  AUTOEXTEND ON NEXT 4096M MAXSIZE 32769M  EXTENT MANAGEMENT LOCAL AUTOALLOCATE
 SEGMENT SPACE MANAGEMENT AUTO" then you can create tables without any additional parameters and everything will be kosher. The tablespace above requires something called "large files support" from the file system and cannot be used on FAT file systems or ISO9660-RR/Joliet file system. Practically anyhing else (UFS,VxFS,ReiserFS,Ext(2|3),XFS,JFS,OCFS,NTFS (scheduled to go away when the new virus propagataion engine enters production)). BTW, what OS and database version do you use?

On 11/07/2003 01:24:25 PM, Maryann Atkinson wrote:
>
> >The answer is that
> >free list handling is overhead, which means that the database is working on
> >its own structures and not working on the user data. It's easy to conceive a
> >busy transaction table to which records are frequently added and from which
> >they're frequently removed. Having only one parameter would significantly
> >increase the amount of time spent in moving blocks to and from the free
> >list,
> >and significantly increase the overhead. You can test it by setting up a
> >table
> >with PCTFREE+PCTUSED=100. In other word, the answer to your question is that
> >two parameters are needed to reduce the overhead of the free list maintenance.
>
> By the way, I just wanted to let you know I tried that PCTFREE+PCTUSED=100
> I used PCTFREE 40 and PCTUSED 60 on a specific table space, and created
> a table there which I updated/deleted records quite a bit, but I didnt see
> much
> of a difference. It might have been because there werent many people
> on the system at the time.
>
> thx
> maa
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Maryann Atkinson
> INET: maryann_30_at_yahoo.com
>
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Mladen Gogala
Oracle DBA

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