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LMT and what is the Bitmap Header Size?

From: <Rajesh.Rao_at_jpmchase.com>
Date: Thu, 08 Aug 2002 10:36:05 -0800
Message-ID: <F001.004AF718.20020808103605@fatcity.com>


I have been struggling to find the right answer to the question: What is the bitmap header size for a uniform extents LMT? 64K, 1 block, 2 blocks????

I find one note on Metalink (Note: 111666.1) that says its 64K .

Mr.Jonathan Lewis says " A quirky little detail about bitmap sizes also came up recently on the Oracle-L mailing list. If you define a very small tablespace - in this context 'very small' means something between 5 blocks and '64K plus one extent' then Oracle will give you a bitmap of just one block - which still allows you to grow the file quite comfortably, of course."

Then another example on Metalink (Note: 109630.1) which goes:

                                                                                                                  
                                                                   SQL> create tablespace mult                    
                                                                     2  datafile                                  
                                                                   '/oracle2/OFA_base/u02/oradata/V816/mult1.dbf' 
                                                                   size 100k,                                     
                                                                     3                                            
                                                                   '/oracle2/OFA_base/u02/oradata/V816/mult2.dbf' 
                                                                   size 100k                                      
                                                                     4  extent management local uniform size 50K; 
                                                                                                                  
                                                                   Tablespace created.                            
                                                                                                                  
                                                                   SQL> select                                    
                                                                   tablespace_name,file_id,block_id,blocks        
                                                                     2   from dba_free_space                      
                                                                     3  where tablespace_name='MULT' ;            
                                                                                                                  
                                                                   TABLESPACE_NAME                   FILE_ID      
                                                                   BLOCK_ID     BLOCKS                            
                                                                   ------------------------------ ----------      
                                                                   ---------- ----------                          
                                                                   MULT                                   15      
                                                                   4         25                                   
                                                                   MULT                                   16      
                                                                   4         25                                   
                                                                                                                  
                                                                   BLOCK_ID=4 : In an ordinary datafile, the      
                                                                   first block where to store data is             
                                                                                block 2.  Therefore, two more     
                                                                   blocks are reserved for the header             
                                                                                bitmap of the locally managed     
                                                                   datafile.                                      
                                                                   BLOCKS=25  : The datafile has a size of 100K   
                                                                   which equals 50 blocks in this                 
                                                                                database =>                       
                                                                                There are only 25 blocks (local   
                                                                   uniform size 50K)left for data                 
                                                                                starting at block n4, then 22    
                                                                   blocks are unused.                             
                                                                                                                  

=> Header bitmap = 2 blocks for each datafile

Moi Confused. Whats the definite word on this? Should be something like if the datafile size is x, then its n, else its some other number.

Thanks
Raj

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Received on Thu Aug 08 2002 - 13:36:05 CDT

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