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Bitmaps means Freelists

Hi,
Can anyone help me in this matter:-

When i was studying locally managed tablespaces i came across bitmaps that are used in locally managed tablespaces it stated that:-
"Locally managed tablespaces use bitmaps stored within the header of the datafiles comprising a tablespace to track the space utilization of the tablespaces."

AND

When i was studying some other topics i came across FreeLists it stated that:-
"Oracle will first search for a free block in the FREELIST and then the data is inserted into that block. The availability of the block in the FREELIST is decided by the PCTFREE value. Initially an empty block will be listed in the FREELIST structure, and it will continue to remain there until the free space reaches the PCTFREE value"

Q) I am confused of Bitmaps and Freelists as they have been used for same purpose whether Bitmaps means Freelists only or is there any difference between them ?


Regards,
Naveen
Jul 30 '07 #1
1 2698
Dave44
153 100+
Hi,
Can anyone help me in this matter:-

When i was studying locally managed tablespaces i came across bitmaps that are used in locally managed tablespaces it stated that:-
"Locally managed tablespaces use bitmaps stored within the header of the datafiles comprising a tablespace to track the space utilization of the tablespaces."

AND

When i was studying some other topics i came across FreeLists it stated that:-
"Oracle will first search for a free block in the FREELIST and then the data is inserted into that block. The availability of the block in the FREELIST is decided by the PCTFREE value. Initially an empty block will be listed in the FREELIST structure, and it will continue to remain there until the free space reaches the PCTFREE value"

Q) I am confused of Bitmaps and Freelists as they have been used for same purpose whether Bitmaps means Freelists only or is there any difference between them ?


Regards,
Naveen
The bitmap they refer to is essentially an index to keep track of space within a datafile, and each datafile within the tablespace will have one. Freelists are used by objects to keep track of blocks of hard drive space for storing data under the high water mark point. when a block reaches the pctfree level (eg if it's 90 then 90% full) then that block is taken off the freelist as it is no longer available for storing new data on. If sufficient rows are deleted from the block such that it reaches the pctused value then that block is put back on the freelist. tablespaces use bitmap indexes to track their space usage. they are not the same thing.
Aug 1 '07 #2

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