Re: Locally managed tablespaces

Considerable overhead? Not really, but I only said "overhead", not "considerable overhead". There are, as you are well aware, potential issues with ST locking on very busy systems with dictionary managed tablespaces. Pre-fragmenting can (not "will") reduce the duration of the ST lock hold. Extent allocation becomes a delete from FET$ and an insert into UET$ rather than an update to FET$ and an insert into UET$. (I hope I got that right!) Its a rather minor tweaker's thing that probably only makes any detectable difference on a handful of systems.

-Don Granaman
[certifiable OraSaurus]

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Monday, July 23, 2001 10:46 AM

> Is there really any considerable overhead involved in dynamically
> allocating an extent? By creating free space chunks in a tablespace
> of uniform extent size, will you really reduce the amount of time and
> resources spent when a segment allocates those extents?
>
> I doubt it, but statistics from v$sesstat could convince me otherwise.
>
> --
> Jeremiah Wilton
> http://www.speakeasy.net/~jwilton
>
> On Sun, 22 Jul 2001, Don Granaman wrote:
>
> > If you are using uniform extents in LMT, you don't want to coalesce
> > - ever. Since every extent will be the same size, it is useless
> > overhead. This is even more true if you have adopted a "uniform
> > extents" policy in any dictionary managed tablespaces. In fact, to
> > reduce the overhead of throwing a new extent in the latter, you
> > might try "pre-fragmenting" the tablespace by creating a junk table
> > in it and manually allocating new extents, then dropping the table -
> > during a low activity period of course.
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Jeremiah Wilton
> INET: jwilton_at_speakeasy.net
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Don Granaman
  INET: granaman_at_home.com

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