一. DB(Data block)
A data block is the smallest unit of storage in an Oracle database. Every database has a default block size (specified when the database is created), although blocks in different tablespaces may have different block sizes.
An extent consist of one or more contiguous Oracle data blocks. A block determines the finest level of granularity of where data can be stored. One data block corresponds to a specific number of bytes of physical space on disk.
Information about data blocks can be retrieved from the data dictionary views USER_SEGMENTS and USER_EXTENTS. These views show how many blocks are allocated for database object and how many blocks are available(free) in a segment/extent.
1.1 Dumping data blocks
Start by getting the file and block number to dump. Example:
SQL> SELECT
2 dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
3 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
4 dbms_rowid.rowid_row_number(rowid) ROWNO,
5 empno, ename
6 FROM emp WHERE empno = 7369;
REL_FNO BLOCKNO ROWNO EMPNO ENAME
---------- ---------- ---------- ---------- ----------
4 20 0 7369 SMITH
Dump the block:
SQL> alter system dump datafile 4 block 20;
System altered.
Look for the newly created dump file in your UDUMP directory.
-- dump 多个blocks
Use the following syntax to dump multiple blocks:
ALTER SYSTEM dump datafile block min block max ;
1.2 Analyzing data block dumps
From the above block dump:
block_row_dump:
tab 0, row 0, @0x1d49
tl: 38 fb: --H-FL-- lb: 0x0 cc: 8
col 0: [ 3] c2 4a 46
col 1: [ 5] 53 4d 49 54 48
col 2: [ 5] 43 4c 45 52 4b
col 3: [ 3] c2 50 03
col 4: [ 7] 77 b4 0c 11 01 01 01
col 5: [ 2] c2 09
col 6: *NULL*
col 7: [ 2] c1 15
Converting back to table values:
Col 0 (EMPNO)
SQL> SELECT utl_raw.cast_to_number(replace(''c2 4a 46'','' '')) value FROM dual;
VALUE
----------
7369
Col 2 (ENAME) - simply convert the hex values to ascii - 53 4d 49 54 48 -> SMITH. Alternatively:
SQL> SELECT utl_raw.cast_to_varchar2(replace(''53 4d 49 54 48'','' '')) value FROM dual;
VALUE
---------
SMITH
二. DBA（Data Block Address）
A Data Block Address (DBA) is the address of an Oracle data block for access purposes.
DBA一般指绝对数据块地址. rowid用来表示一行的物理地址，一行唯一确定一个rowid，并且在使用中一般不会改变，除非rowid之后在行的物理位置发生改变的情况下才会发生变化。在rowid 中，就有一段是来表示DBA的。有关rowid的内容，参考我的Blog：
Oracle Rowid 介绍
2.1 Find the DBA for a given row
Start by getting the file and block number of the row. Example:
SQL> SELECT
2 dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
3 dbms_rowid.rowid_block_number(rowid) BLOCKNO,
4 empno, ename
5 FROM emp WHERE empno = 7369;
REL_FNO BLOCKNO EMPNO ENAME
---------- ---------- ---------- ----------
4 20 7369 SMITH
2.2 convert the file and block numbers to a DBA address:
SQL> variable dba varchar2(30)
SQL> exec :dba := dbms_utility.make_data_block_address(4, 20);
PL/SQL procedure successfully completed.
SQL> print dba
DBA
--------------------------------
16777236
2.3 Convert a DBA back to file and block numbers
Example:
SQL> SELECT dbms_utility.data_block_address_block(16777236) "BLOCK",
2 dbms_utility.data_block_address_file(16777236) "FILE"
3 FROM dual;
BLOCK FILE
---------- ----------
20 4
三. RDBA（Tablespace relative database block address）
在讲RDBA 之前，要先了解下rowid的组成。 关于rowid的内容，参考我的blog：
Oracle Rowid 介绍
http://blog.csdn.net/tianlesoftware/archive/2009/12/16/5020718.aspx
RDBA是相对数据块地址，是数据字典(表空间及一些对象定义)所在块的地址。
oracle 8以后，rowid的存储空间扩大到了10个字节(32bit object#+10bit rfile#+22bit block#+16bit row#)。rdba就是rowid中的rfile#+block#。
SYS@anqing1(rac1)> SELECT
rowid,
dbms_rowid.rowid_relative_fno(rowid) REL_FNO,
dbms_rowid.rowid_block_number(rowid) BLOCKNO,
dbms_rowid.rowid_row_number(rowid) ROWNO,
empno, ename
FROM scott.emp WHERE empno = 7521;
ROWID REL_FNO BLOCKNO ROWNO EMPNO ENAME
------------------ ---------- ---------- ---------- ---------- ----------
AAAMfMAAEAAAAAgAAA 4 32 0 7369 SMITH
rowid = AAAMfMAAEAAAAAgAAA
BlockNo= 4
rowno =0
把这个block dump到trace:
SYS@anqing1(rac1)> alter system dump datafile 4 block 32;
System altered.
查看当前的trace 文件位置：
SYS@anqing1(rac1)> oradebug setmypid;
Statement processed.
SYS@anqing1(rac1)> oradebug tracefile_name
/u01/app/oracle/admin/anqing/udump/anqing1_ora_19997.trc
查看trace file：
[oracle@rac1 ~]$ cat /u01/app/oracle/admin/anqing/udump/anqing1_ora_19997.trc
*** 2011-06-07 11:02:30.023
Start dump data blocks tsn: 4 file#: 4 minblk 32 maxblk 32
buffer tsn: 4 rdba: 0x01000020 (4/32) -- rdba 的值
scn: 0x0000.0006bfdb seq: 0x10 flg: 0x06 tail: 0xbfdb0610
frmt: 0x02 chkval: 0x26a0 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
Dump of memory from 0x0ED09400 to 0x0ED0B400
ED09400 0000A206 01000020 0006BFDB 06100000 [.... ...........]
ED09410 000026A0 00180001 0000C7CC 0006BFD9 [.&..............]
.....
ED094A0 00000000 00000000 00000000 00000000 [................]
Repeat 465 times
ED0B1C0 00000000 08012C00 2350C203 4C494D06 [.....,....P#.MIL]
ED0B1D0 0552454C 52454C43 4EC2034B B6770753 [LER.CLERK..NS.w.]
....
ED0B3E0 05485449 52454C43 50C2034B B4770703 [ITH.CLERK..P..w.]
ED0B3F0 0101110C 09C20201 15C102FF BFDB0610 [................]
Block header dump: 0x01000020
Object id on Block? Y
seg/obj: 0xc7cc csc: 0x00.6bfd9 itc: 2 flg: E typ: 1 - DATA
brn: 0 bdba: 0x1000019 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x0003.011.000000f2 0x00805794.00c8.49 --U- 14 fsc 0x0000.0006bfdb
0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000
data_block_dump,data header at 0xed09464
===============
tsiz: 0x1f98
hsiz: 0x2e
pbl: 0x0ed09464
bdba: 0x01000020
76543210
flag=--------
ntab=1
nrow=14
frre=-1
fsbo=0x2e
fseo=0x1d61
avsp=0x1d33
tosp=0x1d33
0xe:pti[0] nrow=14 offs=0 -- 该块中保存了14条记录。从row 0到row 13
0x12:pri[0] offs=0x1f72
0x14:pri[1] offs=0x1f47
0x16:pri[2] offs=0x1f1c
0x18:pri[3] offs=0x1ef3
0x1a:pri[4] offs=0x1ec6
0x1c:pri[5] offs=0x1e9d
0x1e:pri[6] offs=0x1e74
0x20:pri[7] offs=0x1e4c
0x22:pri[8] offs=0x1e26
0x24:pri[9] offs=0x1dfb
0x26:pri[10] offs=0x1dd5
0x28:pri[11] offs=0x1daf
0x2a:pri[12] offs=0x1d88
0x2c:pri[13] offs=0x1d61
block_row_dump:
tab 0, row 0, @0x1f72
tl: 38 fb: --H-FL-- lb: 0x1 cc: 8
col 0: [ 3] c2 4a 46
col 1: [ 5] 53 4d 49 54 48
col 2: [ 5] 43 4c 45 52 4b
col 3: [ 3] c2 50 03
col 4: [ 7] 77 b4 0c 11 01 01 01
col 5: [ 2] c2 09
col 6: *NULL*
col 7: [ 2] c1 15
tab 0, row 1, @0x1f47
tl: 43 fb: --H-FL-- lb: 0x1 cc: 8
col 0: [ 3] c2 4b 64
col 1: [ 5] 41 4c 4c 45 4e
col 2: [ 8] 53 41 4c 45 53 4d 41 4e
col 3: [ 3] c2 4d 63
col 4: [ 7] 77 b5 02 14 01 01 01
col 5: [ 2] c2 11
col 6: [ 2] c2 04
col 7: [ 2] c1 1f
tab 0, row 2, @0x1f1c
tl: 43 fb: --H-FL-- lb: 0x1 cc: 8
col 0: [ 3] c2 4c 16
col 1: [ 4] 57 41 52 44
col 2: [ 8] 53 41 4c 45 53 4d 41 4e
col 3: [ 3] c2 4d 63
col 4: [ 7] 77 b5 02 16 01 01 01
col 5: [ 3] c2 0d 33
col 6: [ 2] c2 06
col 7: [ 2] c1 1f
tab 0, row 3, @0x1ef3
...
tl: 39 fb: --H-FL-- lb: 0x1 cc: 8
col 0: [ 3] c2 50 23
col 1: [ 6] 4d 49 4c 4c 45 52
col 2: [ 5] 43 4c 45 52 4b
col 3: [ 3] c2 4e 53
col 4: [ 7] 77 b6 01 17 01 01 01
col 5: [ 2] c2 0e
col 6: *NULL*
col 7: [ 2] c1 0b
end_of_block_dump
End dump data blocks tsn: 4 file#: 4 minblk 32 maxblk 32
[oracle@rac1 ~]$
/* Formatted on 2011/6/7 11:27:10 (QP5 v5.163.1008.3004) */
SELECT DBMS_UTILITY.data_block_address_file (
TO_NUMBER (LTRIM (''0x01000020'', ''0x''), ''xxxxxxxx''))
AS file_no,
DBMS_UTILITY.data_block_address_block (
TO_NUMBER (LTRIM (''0x01000020'', ''0x''), ''xxxxxxxx''))
AS block_no
FROM DUAL;
FILE_NO BLOCK_NO
---------- ----------
4 32
这个和我们之前在rowid里查看的一致。
刚才说了，在32这个块里保存了14条row记录，我们继续查询一下我们where=7521 那条：
tab 0, row 13, @0x1d61
SYS@anqing1(rac1)> select DBMS_UTILITY.data_block_address_block (TO_NUMBER (LTRIM (''0x1d61'', ''0x''),''xxxxxxxx'')) as block_no from dual;
BLOCK_NO
----------
7521
我们查询的那条row记录在最后一条。