Re: Locally managed tablespaces

From: Jared Still <jkstill_at_bcbso.com>
Date: Mon, 19 Jun 2000 11:29:17 -0700 (PDT)
Message-Id: <10533.109744@fatcity.com>

On Mon, 19 Jun 2000, Madhavan Amruthur wrote:

>
> But is this normal behaviour for locally managed tablespaces that an extent
> from each datafile is grabbed?
>

yup.

Doc ID:

           Note:111666.1
  Subject:

           Locally managed tablespace with uniform extent size use
           one extent per datafile
  Type: 
           BULLETIN
  Status: 
           REVIEWED

                                                                 Content Type: 
                                                                                     TEXT/PLAIN
                                                                 Creation Date: 
                                                                                     02-JUN-2000
                                                                 Last Revision Date: 
                                                                                     09-JUN-2000
                                                                 Language: 
                                                                                     USAENG



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  PURPOSE

---

  To explain the consequence of using locally managed tablespaces with   a large UNIFORM extent size.    

  SCOPE & APPLICATION

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  DBA's creating locally managed tablespaces with a UNIFORM extent size   should understand the ramifications of their choices on the overhead   of space used to store the storage management (bitmap) information.

  Locally managed tablespace with uniform extent size use one extent per datafile

---

   

  When creating tablespaces with a uniform extent size it is important to understand   that one extent per datafile is allocated for the storage management information.

  Consider the following example to illustrate the matter:

  SVRMGR> create tablespace locally_managed                                       
       2> datafile '/server0/oradata/v816/lm01.dbf' size 10 m                     
       3> extent management local uniform size 5 m;                               
  Statement processed.                                                            

  SVRMGR> select bytes from dba_free_space where                                  
       2> TABLESPACE_NAME = 'LOCALLY_MANAGED';                                    

       BYTES                                                                           
  ----------                                                                      
     5242880          

  The same holds for all datafiles that are added to this tablespace:

  SVRMGR> alter tablespace locally_managed add datafile                           
       2> '/server0/oradata/v816/lm02.dbf' size 10 m;                             
  Statement processed.                                                            

  SVRMGR> select bytes from dba_free_space where                                  
       2> TABLESPACE_NAME = 'LOCALLY_MANAGED';                                    

       BYTES                                                                           
  ----------                                                                      
     5242880                                                                      
     5242880                                                                      

  This behaviour is documented in Documentation bug 763982 as follows:            

  When creating a datafile/tempfile on a locally managed tablespace, we need to   
  allocate the header for the datafile, the bitmap for the extent map in the      

  tablespace, and at least one extent (by default, 512 db blocks).

  The credo with UNIFORM extents size in locally managed tablespaces is           
  therefore that the size should be only a marginal fraction of the               

  datafile(s) size in order to minimize space management overhead.

  RELATED DOCUMENTS

---

  bug 763982 NEED TO IMPROVE DOCUMENTATION ABOUT LOCALLY MANAGED TABLESPACES   Note:109627.1 Migrating a tablespace from a dictionary to a local management requires space Received on Mon Jun 19 2000 - 13:29:17 CDT