>From the 'Data Management and Storage Internal" notes,
Bitmapped Tablespace File Structure
A new bitmapped tablespace file has the following structure:
File Header 1 block
Bitmapped File Space Header 1 block
Head portion of of Bitmap Blocks N blocks
Useful file blocks U units (A unit is a number
of blocks)
Tail portion of Bitmap Blocks M blocks
If a Unit = B blocks, then the total file size = 1 + 1 + N + U*B + M
Bitmapped File Space Header
...... (lots to type, I can if you really need it)
Bitmap blocks have 2 parts :
Bitmap control structure
Vector Dump
The fields in the bitmap control structure are:
RelFNo: Relative file number to which the bitmap belongs
BeginBlock: Which block number does the first bit represent
Flag: Zero for permanent files, one for temp files
First: Where to start looking for the free space (bit before first free
bit)
Free: Number of free slots (bits) in the bitmap (not the file)
To read the bitmap, take each two-byte pair, least significant bit first.
If there are not eight bits, pad to eight bits with zeroes. Hence 0x0F = 15
= 00001111. When written least significant bit first, the bitmap looks like
this
11110000 --> used, used, used, used, free, free, free, free
Scanning for the first free extent will start at the 4th bit.
HTH
Paul
-----Original Message-----
Sent: Monday, April 08, 2002 3:44 PM
To: Multiple recipients of list ORACLE-L
Out of curiosity I decided I wanted to look at what composed the
extent map in locally-managed tablespaces.
I dumped the first 5 blocks of the tablespace's first datafile with
'alter system dump datafile ...' The results surprised me, as they
appeared to consist of almost no data. The LMT in question contains a
variety of segments and extents. How is the LMT bitmap organized?
Start dump data blocks tsn: 1 file#: 2 minblk 1 maxblk 1
Block 1 (file header) not dumped: use dump file header command
Start dump data blocks tsn: 1 file#: 2 minblk 2 maxblk 2
frmt: 0x02 chkval: 0x0000 type: 0x1d=KTFB Bitmapped File Space Header
File Space Header Block:
Header Control:
RelFno: 2, Unit: 8192, Size: 524352, Flag: 1
Initial Area: 3, Tail: 524292, First: 30, Free: 34
Start dump data blocks tsn: 1 file#: 2 minblk 3 maxblk 3
frmt: 0x02 chkval: 0x0000 type: 0x1e=KTFB Bitmapped File Space Bitmap
File Space Bitmap Block:
BitMap Control:
RelFno: 2, BeginBlock: 5, Flag: 0, First: 30, Free: 128994
FFFFFF3F00000000 0000000000000000 0000000000000000 0000000000000000
0000000000000000 0000000000000000 0000000000000000 0000000000000000
0000000000000000 0000000000000000 0000000000000000 0000000000000000
... all zeros
Start dump data blocks tsn: 1 file#: 2 minblk 4 maxblk 4
frmt: 0x02 chkval: 0x0000 type: 0x1e=KTFB Bitmapped File Space Bitmap
File Space Bitmap Block:
BitMap Control:
RelFno: 2, BeginBlock: 1056964613, Flag: 0, First: 0, Free: 129024
0000000000000000 0000000000000000 0000000000000000 0000000000000000
0000000000000000 0000000000000000 0000000000000000 0000000000000000
0000000000000000 0000000000000000 0000000000000000 0000000000000000
... all zeros
FWIW:
SQL> select count (*) from dba_extents where file_id = 2;
COUNT(*)
----------
30
SQL> select extent_management from dba_data_files df, dba_tablespaces
ts where df.tablespace_name = ts.tablespace_name and file_id = 2;
EXTENT_MAN
----------
LOCAL
--
Jeremiah Wilton
http://www.speakeasy.net/~jwilton
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Author: Jeremiah Wilton
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