Oracle rdba和 dba 說明

一. DB(Data block)

From: http://www.orafaq.com/wiki/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 多個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）

From：http://www.orafaq.com/wiki/Data_block_address

A Data Block Address (DBA) is the address of an Oracle data block for access purposes.

DBA一般指絕對資料塊地址. rowid用來表示一行的實體地址，一行唯一確定一個rowid，並且在使用中一般不會改變，除非rowid之後在行的物理位置發生改變的情況下才會發生變化。在rowid 中，就有一段是來表示DBA的。有關rowid的內容，參考我的Blog：

Oracle Rowid 介紹

http://space.itpub.net/28673746/viewspace-757345

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）

在講RDBA 之前，要先了解下rowid的組成。 關於rowid的內容，參考我的blog：

Oracle Rowid 介紹

http://space.itpub.net/28673746/viewspace-757345

RDBA是相對資料塊地址，是資料字典(表空間及一些物件定義)所在塊的地址。

oracle 8以後，rowid的儲存空間擴大到了10個位元組(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

把這個block dump到trace:

SYS@anqing1(rac1)> alter system dump datafile 4 block 32;

System altered.

檢視當前的trace 檔案位置：

SYS@anqing1(rac1)> oradebug setmypid;

Statement processed.

SYS@anqing1(rac1)> oradebug tracefile_name

/u01/app/oracle/admin/anqing/udump/anqing1_ora_19997.trc

檢視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 ffs=0 -- 該塊中儲存了14條記錄。從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

...

tab 0, row 13, @0x1d61

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

這個和我們之前在rowid裡檢視的一致。

剛才說了，在32這個塊裡儲存了14條row記錄，我們繼續查詢一下我們where=7521 那條：

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

我們查詢的那條row記錄在最後一條。

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