oracle flashback 深入研究,oracle 之flashback 深入研究。

oracle 之flashback 深入研究。

今天是2013-08-24，开始进行oracle flashback 内部原理研究，记录一下笔记。

SQL> startup

ORACLE instance started.

Total System Global Area 405020672 bytes

Fixed Size 2213816 bytes

Variable Size 260048968 bytes

Database Buffers 138412032 bytes

Redo Buffers 4345856 bytes

Database mounted.

Database opened.

SQL>

SQL> select * from t1;

ID SAL JOB

---------- ---------- ----------

1 9 z

1 2 a

2 3 b

3 4 c

1 3 b

2 1 a

7 rows selected.

SQL> select xidusn,ubafil,ubablk from v$transaction;

no rows selected

SQL> delete from t1 where id=3;

1 row deleted.

SQL> select xidusn,ubafil,ubablk from v$transaction;

XIDUSN UBAFIL UBABLK

---------- ---------- ----------

17 8 2583

SQL> alter system dump datafile 8 block 2583;

System altered.

SQL> set vlaue for a60

SP2-0158: unknown SET option "vlaue"

SQL> col value for a60

SQL> set linesize 200

SQL> select * from v$diag_info where name='Default Trace File';

INST_ID NAME VALUE

---------- ---------------------------------------------------------------- ------------------------------------------------------------

1 Default Trace File /opt/app/oracle/diag/rdbms/rhys/RHYS/trace/RHYS_ora_1801.trc

SQL> commit;

Commit complete.

UNDO BLK:

xid: 0x0011.019.000000b4 seq: 0x23c cnt: 0x46 irb: 0x46 icl: 0x0 flg: 0x0000

Rec Offset Rec Offset Rec Offset Rec Offset Rec Offset

---------------------------------------------------------------------------

0x01 0x1f90 0x02 0x1f4c 0x03 0x1ef4 0x04 0x1eb0 0x05 0x1e58

0x06 0x1e14 0x07 0x1dbc 0x08 0x1d78 0x09 0x1d20 0x0a 0x1cdc

0x0b 0x1c84 0x0c 0x1c40 0x0d 0x1be8 0x0e 0x1ba4 0x0f 0x1b4c

0x10 0x1b08 0x11 0x1ab0 0x12 0x19d0 0x13 0x18f0 0x14 0x1868

0x15 0x1800 0x16 0x1794 0x17 0x1620 0x18 0x1508 0x19 0x1480

0x1a 0x1414 0x1b 0x13a8 0x1c 0x1224 0x1d 0x119c 0x1e 0x1134

0x1f 0x10c8 0x20 0x0f4c 0x21 0x0edc 0x22 0x0e54 0x23 0x0de8

0x24 0x0d7c 0x25 0x0d38 0x26 0x0ca0 0x27 0x0c14 0x28 0x0bd0

0x29 0x0b74 0x2a 0x0b18 0x2b 0x0ad4 0x2c 0x0a78 0x2d 0x0a1c

0x2e 0x09d8 0x2f 0x097c 0x30 0x0920 0x31 0x08dc 0x32 0x0880

0x33 0x0824 0x34 0x07dc 0x35 0x0778 0x36 0x071c 0x37 0x06d8

0x38 0x067c 0x39 0x0620 0x3a 0x05dc 0x3b 0x0580 0x3c 0x0524

0x3d 0x04e0 0x3e 0x0484 0x3f 0x0428 0x40 0x0340 0x41 0x02b4

0x42 0x0250 0x43 0x01e8 0x44 0x016c 0x45 0x0114 0x46 0x00d0

*-----------------------------

* Rec #0x22 slt: 0x19 objn: 468(0x000001d4) objd: 468 tblspc: 1(0x00000001)

* Layer: 11 (Row) opc: 1 rci 0x00

Undo type: Regular undo Begin trans Last buffer split: No

Temp Object: No

Tablespace Undo: No

rdba: 0x00000000Ext idx: 0

flg2: 0

*-----------------------------

uba: 0x02000a17.023c.21 ctl max scn: 0x0000.00a82f35 prv tx scn: 0x0000.00a82f6f

txn start scn: scn: 0x0000.00a83315 logon user: 0

prev brb: 33580056 prev bcl: 0

KDO undo record:

KTB Redo

op: 0x04 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: L itl: xid: 0x0010.000.000000cb uba: 0x02006433.024f.39

flg: C--- lkc: 0 scn: 0x0000.00a832c7

KDO Op code: DRP row dependencies Disabled

xtype: XA flags: 0x00000000 bdba: 0x0080f7a9 hdba: 0x0080039a

itli: 1 ispac: 0 maxfr: 4858

tabn: 0 slot: 27(0x1b)

SQL> select to_number('a82f35','xxxxxxxxxxxxxxxx') sc from dual;

----------

11022133

SQL> select current_scn from v$database;

CURRENT_SCN

-----------

11054748

SQL>

注意：闪回查询和undo_retention有直接关系；

eg：

SQL> update t1 set job='ab' where id=1;

3 rows updated.

SQL> select versions_starttime,versions_endtime,versions_xid,versions_operation,id,sal from t1 versions between timestamp minvalue and maxvalue

2 ;

VERSIONS_STARTTIME VERSIONS_ENDTIME VERSIONS_XID V ID SAL

--------------------------------------------------------------------------- -------------------- ---------------- - ---------- ----------

1 9

1 2

2 3

1 3

2 1

6 rows selected.

SQL> show parameter undo

NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

_optimizer_undo_cost_change string 11.2.0.1

_undo_autotune boolean FALSE

undo_management string AUTO

undo_retention integer 60

undo_tablespace string UNDOTBS3

SQL> alter system set undo_retention=1800;

System altered.

SQL> select versions_starttime,versions_endtime,versions_xid,versions_operation,id,sal from t1 versions between timestamp minvalue and maxvalue;

VERSIONS_STARTTIME VERSIONS_ENDTIME VERSIONS_XID V ID SAL

--------------------------------------------------------------------------- -------------------- ---------------- - ---------- ----------

1 9

24-AUG-13 09.49.38 PM 11000300BF000000 D 3 4

1 2

2 3

24-AUG-13 09.49.38 P 3 4

1 3

2 1

8 rows selected.

1)闪回查询：

SQL> select * from t1 ;

ID SAL JOB

---------- ---------- ----------

1 9 z

1 2 a

2 3 b

1 3 b

2 1 a

6 rows selected.

SQL> select * from t1 as of scn 11022133;

ID SAL JOB

---------- ---------- ----------

1 2 a

2 3 b

3 4 c

1 3 b

2 1 a

6 rows selected.

SQL>

2)闪回版本查询：

SQL> r

1* select * from t1

ID SAL JOB

---------- ---------- ----------

1 9 ab

1 2 ab

2 3 b

1 3 ab

2 1 a

6 rows selected.

SQL> delete from t1 where id=1;

3 rows deleted.

SQL> commit;

Commit complete.

SQL> select versions_startscn,versions_endscn,versions_xid,versions_operation,id,sal,job from t1 versions between scn minvalue and maxvalue;

VERSIONS_STARTSCN VERSIONS_ENDSCN VERSIONS_XID V ID SAL JOB

----------------- --------------- ---------------- - ---------- ---------- ----------

11144497 0D001600D8000000 D 1 9 z

11144497 1 9 z

11144497 0D001600D8000000 D 1 3 b

11144497 0D001600D8000000 D 1 2 a

11054404 11000300BF000000 D 3 4 c

11144497 1 2 a

2 3 b

11054404 3 4 c

11144497 1 3 b

2 1 a

11 rows selected.

SQL>

然后我们更具versions_xid找到相应的事务

3)事务查询；

借助flashback_transaction_query这个视图；

首先看一下这个视图结构；

SSQL> desc flashback_transaction_query;

Name Null? Type

----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------

XID RAW(8)

START_SCN NUMBER

START_TIMESTAMP DATE

COMMIT_SCN NUMBER

COMMIT_TIMESTAMP DATE

LOGON_USER VARCHAR2(30)

UNDO_CHANGE# NUMBER

OPERATION VARCHAR2(32)

TABLE_NAME VARCHAR2(256)

TABLE_OWNER VARCHAR2(32)

ROW_ID VARCHAR2(19)

UNDO_SQL VARCHAR2(4000)

SQL>

然后我们进行一次查询：

eg：

SQL> conn rhys/root

Connected.

SQL> select * from t1;

ID SAL JOB

---------- ---------- ----------

2 3 b

3 1 a

1 1 ab

SQL> delete from t1 where id=1;

1 row deleted.

SQL> commit;

Commit complete.

SQL> select versions_startscn,versions_endscn,versions_xid,versions_operation,id,sal,job from t1 versions between scn minvalue and maxvalue;

VERSIONS_STARTSCN VERSIONS_ENDSCN VERSIONS_XID V ID SAL JOB

----------------- --------------- ---------------- - ---------- ---------- ----------

11166640 13000A00D9000000 U 3 1 a

2 3 b

11166640 2 1 a

11187698 13001300DB000000 D 1 1 ab

11166640 11187698 13000A00D9000000 I 1 1 ab

6 rows selected.

SQL> select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid='13000A00D9000000';

select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid='13000A00D9000000'

ERROR at line 1:

ORA-01031: insufficient privileges

SQL> conn sys/root as sysdba

Connected.

SQL> select current_scn from v$database;

CURRENT_SCN

-----------

11187761

SQL> select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid='13001300DB000000';

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

ROW_ID

-------------------

UNDO_SQL

13001300DB000000 RHYS 0 UNKNOWN

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

ROW_ID

-------------------

UNDO_SQL

13001300DB000000 RHYS 0 BEGIN

SQL>

但是没有任何undo_sql，查看网络发现如下：

#这里执行这个语句的意思是追加日志

supplemental logging 的定义：

redo log一般用于实例恢复及介质恢复。在redo log中这些数据被自动记录。不过一些

基于redo的application可能在redo log中记录额外的一些列。这种记录额外列的过程

被称为supplemental logging

缺省情况下，数据库没有打开对supplemental logging的支持。

然后重新做实验如下：

SQL> alter database add supplemental log data;

Database altered.

SQL> select * from t1;

ID SAL JOB

---------- ---------- ----------

2 3 b

2 1 a

SQL> update t1 set id=3 where job='D';

1 row updated.

SQL> commit;

Commit complete.

SQL> select versions_startscn,versions_endscn,versions_xid,versions_operation,id,sal,job from t1 versions between scn minvalue and maxvalue;

VERSIONS_STARTSCN VERSIONS_ENDSCN VERSIONS_XID V ID SAL JOB

----------------- --------------- ---------------- - ---------- ---------- ----------

11144497 0D001600D8000000 D 1 9 z

11144497 1 9 z

11211146 0B001600DF000000 U 3 D

11144497 0D001600D8000000 D 1 3 b

11144497 0D001600D8000000 D 1 2 a

11144497 1 2 a

2 3 b

11144497 1 3 b

2 1 a

11211146 D

10 rows selected.

SQL> select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid='0B001600DF000000';

^CERROR:

ORA-01013: user requested cancel of current operation

no rows selected

SQL> set timing on

SQL> r

1* select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid='0B001600DF000000'

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

ROW_ID

-------------------

UNDO_SQL

0B001600DF000000 SYS 11211144 UPDATE

AAASCgAAFAAAACHAAF

update "SYS"."T1" set "ID" = NULL where ROWID = 'AAASCgAAFAAAACHAAF';

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

ROW_ID

-------------------

UNDO_SQL

0B001600DF000000 SYS 11211144 BEGIN

Elapsed: 00:03:40.77

SQL>

可以看到sql了。

那么之前的事务是不是也能自动再重新记录sql呢？答案是否定的如下：

SQL> select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid=hextoraw('13001300DB000000');

XID LOGON_USER START_SCN OPERATION TABLE_NAME ROW_ID UNDO_SQL

---------------- ------------------------------ ---------- -------------------------------- -------------------------------------------------------------------------------- ------------------- --------------------------------------------------------------------------------

13001300DB000000 RHYS 0 UNKNOWN T1

13001300DB000000 RHYS 0 BEGIN

Executed in 0.063 seconds

SQL>

另外一个问题就来了，这个查询过程也忒慢了吧。因为xid为raw类型。这时候为了提高查询速度使用hextoraw进行转换，使用内部索引来提高查询速度。

eg：

SQL> set autotrace on

SQL> select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid=hextoraw('0B001600DF000000');

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

ROW_ID

-------------------

UNDO_SQL

0B001600DF000000 SYS 11211144 UPDATE

AAASCgAAFAAAACHAAF

update "SYS"."T1" set "ID" = NULL where ROWID = 'AAASCgAAFAAAACHAAF';

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

ROW_ID

-------------------

UNDO_SQL

0B001600DF000000 SYS 11211144 BEGIN

Elapsed: 00:00:00.03

Execution Plan

----------------------------------------------------------

Plan hash value: 1747778896

---------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | 2197 | 0 (0)| 00:00:01 |

|* 1 | FIXED TABLE FIXED INDEX| X$KTUQQRY (ind:1) | 1 | 2197 | 0 (0)| 00:00:01 |

---------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - filter("XID"=HEXTORAW('0B001600DF000000') )

Statistics

----------------------------------------------------------

36 recursive calls

1 db block gets

51 consistent gets

0 physical reads

0 redo size

1139 bytes sent via SQL*Net to client

523 bytes received via SQL*Net from client

2 SQL*Net roundtrips to/from client

3 sorts (memory)

0 sorts (disk)

2 rows processed

SQL>

对比一下：

SQL> select xid,logon_user,start_scn,operation,table_name,row_id,undo_sql from flashback_transaction_query where xid='0B001600DF000000';

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

ROW_ID

-------------------

UNDO_SQL

0B001600DF000000 SYS 11211144 UPDATE

AAASCgAAFAAAACHAAF

update "SYS"."T1" set "ID" = NULL where ROWID = 'AAASCgAAFAAAACHAAF';

XID LOGON_USER START_SCN OPERATION

---------------- ------------------------------ ---------- --------------------------------

TABLE_NAME

ROW_ID

-------------------

UNDO_SQL

0B001600DF000000 SYS 11211144 BEGIN

Elapsed: 00:03:51.14

Execution Plan

----------------------------------------------------------

Plan hash value: 1115820779

------------------------------------------------------------------------------

------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | 2197 | 0 (0)| 00:00:01 |

|* 1 | FIXED TABLE FULL| X$KTUQQRY | 1 | 2197 | 0 (0)| 00:00:01 |

------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - filter(RAWTOHEX("XID")='0B001600DF000000')

Statistics

----------------------------------------------------------

2936981 recursive calls

10 db block gets

3772792 consistent gets

14256 physical reads

0 redo size

1139 bytes sent via SQL*Net to client

523 bytes received via SQL*Net from client

2 SQL*Net roundtrips to/from client

731820 sorts (memory)

0 sorts (disk)

2 rows processed

SQL>

这就是闪回查询，闪回版本查询，闪回事务查询。

oracle flashback 深入研究,oracle 之flashback 深入研究。

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