DBA Tips Archive for Oracle


Segment Space Management in Locally Managed Tablespaces - (Oracle 9i)

by Jeff Hunter, Sr. Database Administrator


  1. Overview
  2. Segment Space Management Options
  3. Syntax
  4. Limitations


Beginning with Oracle8i, DBAs have the opportunity of creating locally managed tablespaces which use bitmaps to manage extents. Prior to Oracle8i, DBAs only had the option of creating dictionary-managed tablespaces. Dictionary-managed tablespaces use and update the data dictionary whenever an extent is allocated, or freed for reuse, causing excessive internal locking.

New with Oracle9i, DBAs can now take it one step further by applying the same technique in determining how free and used space within a segment is to be managed within locally managed tablespaces. This article provides a brief overview of automatic segment-space management as well as some of its limitations.

Segment Space Management Options

In Oracle9i, DBAs have two choices for segment-space management; manual (the default) and auto.

Prior to Oracle9i, free lists have been the only option for managing free space within a segment. Using bitmaps, however, provide a simpler and more efficient way of managing segment free space. They not only provide better space utilization, but eliminate any need to specify and the tune PCTUSED, PCTFREE, FREELISTS and FREELIST GROUPS parameters. If any of these parameters are specified during segment creation while using the automatic segment space management option, they are simply ignored.


  DATAFILE '/u10/app/oradata/ORA901/users01.dbf' SIZE 10M REUSE


Copyright (c) 1998-2018 Jeffrey M. Hunter. All rights reserved.

All articles, scripts and material located at the Internet address of http://www.idevelopment.info is the copyright of Jeffrey M. Hunter and is protected under copyright laws of the United States. This document may not be hosted on any other site without my express, prior, written permission. Application to host any of the material elsewhere can be made by contacting me at jhunter@idevelopment.info.

I have made every effort and taken great care in making sure that the material included on my web site is technically accurate, but I disclaim any and all responsibility for any loss, damage or destruction of data or any other property which may arise from relying on it. I will in no case be liable for any monetary damages arising from such loss, damage or destruction.

Last modified on
Friday, 20-Jan-2006 15:48:22 EST
Page Count: 26236