Topic: Database Administration >> Space Management
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| Navi |
Posted: Sep 01, 2007 02:17:35 AM |
Total Post: 60
Joined: Jun, 2007
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Hi,
Free space management is important because without it oracle would not
know where to put things like tables or indexes when you wanted to
create or modify them.
Locally managed tablespace use Bitmaps stored in the header of the
datafiles.
Question:-
In Bitmap whether each bit represents the extent of the Datafile or
each block of the Datafile?
If Each bit represents the extent of the datafile, then whether this
statement is true:-
When all the blocks of the extent is used or freed, then only oracle
changes the bitmap values to show the new status of the extent.
If Each bit represents the block of the datafile then whether this
statement is true:-
Whenever each block is used or freed oracle changes the bitmap values to
show the new status of the blocks.
Please Guide me.
Regards,
Naveen |
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 meraj |
| Posted: Sep 08, 2007 04:56:39 AM |  |
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Total Post: 40
Joined: Sep, 2006
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Frankly this is not clear to me also....... Please someone help on this.
Meraj
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| Navi |
| Posted: Sep 08, 2007 07:33:52 AM | |
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Total Post: 60
Joined: Jun, 2007
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Hi,
Locally managed tablespaces have a bitmap in the header of datafiles to manage the extent allocation.
It is not exactly a bit per extent because tablespaces may have non uniform size of extent.
So, the bitmap is updated when extents are allocated (not blocks) or deallocated.
It is the same as in dictionary managed tablespaces where a row is inserted in SYS.UET$ and SYS.FET$.
Nothing is done here at block level.Remember you can have extents allocated even if they have only empty blocks (when you do alter table ... allocate extent for example).
However, a locally managed tablespace may have automatic segment space management (instead of freelist) that manages the segment blocks usage.
But that is a different thing, it is a bitmap in the segment header, and here it is managed at block level.
Regards,
Naveen
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