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
D
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;
SC
----------
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
M
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
D
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
D
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
D
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
D
11 rows selected.
SQL>
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
D
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
D
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
T1
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
D
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
T1
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
T1
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
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 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
T1
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
------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------
| 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。