blocks,extents,segments

<pre name="code" class="sql"><pre name="code" class="sql">Block: Oracle存储的最小单位

Extent：

EXTENT_ID	NUMBER	 	Extent number in the segment

BLOCK_ID	NUMBER	 	Starting block number of the extent

BLOCKS	NUMBER	 	Size of the extent in Oracle block

SQL> set linesize 200
SQL> select owner,segment_name,extent_id,file_id,block_id,blocks from dba_extents  where owner='TEST' and segment_name='BFW_TEST';

OWNER			       SEGMENT_NAME									  EXTENT_ID    FILE_ID	 BLOCK_ID     BLOCKS
------------------------------ --------------------------------------------------------------------------------- ---------- ---------- ---------- ----------
TEST			       BFW_TEST 										  0	     6	     5376	 128
TEST			       BFW_TEST 										  1	     6	     1792	 128
TEST			       BFW_TEST 										  2	     6	     1920	 128
TEST			       BFW_TEST 										  3	     6	     2048	 128
TEST			       BFW_TEST 										  4	     6	     2176	 128
TEST			       BFW_TEST 										  5	     6	     3712	 128
TEST			       BFW_TEST 										  6	     6	     3840	 128
TEST			       BFW_TEST 										  7	     6	     3968	 128
TEST			       BFW_TEST 										  8	     6	     4096	 128

已选择9行。


select owner,segment_name,header_file,header_block,blocks,extents from dba_segments where owner='TEST' and segment_name='BFW_TEST'SQL> SQL> ;

OWNER			       SEGMENT_NAME									 HEADER_FILE HEADER_BLOCK     BLOCKS	EXTENTS
------------------------------ --------------------------------------------------------------------------------- ----------- ------------ ---------- ----------
TEST			       BFW_TEST 										   6	     5376	1152	      9

HEADER_FILE	NUMBER	 	ID of the file containing the segment header

HEADER_BLOCK	NUMBER	 	ID of the block containing the segment header


BLOCKS	NUMBER	 	Size, in Oracle blocks, of the segment  --segment的块数 = 128 * 9

EXTENTS	NUMBER	 	Number of extents allocated to the segment

SQL> select owner,segment_name,extent_id,file_id,block_id,blocks from dba_extents  where owner='TEST' and segment_name='TEST';


OWNER			       SEGMENT_NAME									  EXTENT_ID    FILE_ID	 BLOCK_ID     BLOCKS
------------------------------ --------------------------------------------------------------------------------- ---------- ---------- ---------- ----------
TEST			       TEST											  0	    10	    15232	 128
TEST			       TEST											  1	     6	    18432	 128
TEST			       TEST											  2	    10	    15360	 128
TEST			       TEST											  3	     6	    19200	 128
TEST			       TEST											  4	    10	    15488	 128
TEST			       TEST											  5	     6	    19328	 128
TEST			       TEST											  6	    10	    15616	 128
TEST			       TEST											  7	     6	    19456	 128
TEST			       TEST											  8	    10	    15744	 128

但是segment上的block不一定连续,extent 不能跨数据文件(因为extent都是连续的block)
segment不可以跨表空间但可以跨数据文件