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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Decyphering LMT space bitmap
>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
-- Jeremiah Wilton http://www.speakeasy.net/~jwilton -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Jeremiah Wilton INET: jwilton_at_speakeasy.net Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: Paul.Parker_at_bmwna.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Mon Apr 08 2002 - 15:23:27 CDT
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