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update 一条话语的来龙去脉

2013-10-25 
update 一条语句的来龙去脉! update 一条语句的来龙去脉!今天是2013-10-24,在今天翻电脑资料的时候看到了

update 一条语句的来龙去脉!

 update 一条语句的来龙去脉!

     今天是2013-10-24,在今天翻电脑资料的时候看到了如下一个图,随即兴致盎然的在一次研究了一下内部过程。

update 一条话语的来龙去脉

容易混淆的知识点:

uba=0x00800055.02de.3f
0x00800055代表数据的前镜像
seq:代表是顺序号
3f,是undo记录的开始地址(irb信息)

xid=0x0006.018.000036ce
该事务指向6号回滚段,slot好为0x17,wrap#为36ce
xid=undo.segment.number+transaction.table.slot.number+wrap;

dba:包含这个事务的前镜像的数据块地址:转换为二进制,然后转换为前22为块后10数据文件号

bdba:0x00405c5a 记录了更改数据块的地址。

session 1:
  首先切换一下redo,保证新产生的redo条目存在于干净的redo file中:

SQL> alter system switch logfile;

System altered.

SQL> select * from v$log;   

    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE    MEMBERS ARC STATUS           FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
         1          1        364   52428800        512          1 NO  CURRENT                5294094 24-OCT-13   2.8147E+14
         2          1        362   52428800        512          1 YES INACTIVE               5293624 24-OCT-13      5294000 24-OCT-13
         3          1        363   52428800        512          1 YES ACTIVE                 5294000 24-OCT-13      5294094 24-OCT-13

SQL> conn rhys/amy
Connected.
SQL> select * from emp;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      7500 AMY        CLERK           7902 17-DEC-80        800                    20
      7499 amy        SALESMAN        7698 20-FEB-81       1600        300         30
      7521 WARD       SALESMAN        7698 22-FEB-81       1250        500         30
      7566 JONES      MANAGER         7839 02-APR-81       2975                    20
      7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
      7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
      7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
      7788 SCOTT      ANALYST         7566 19-APR-87       3000                    20
      7839 KING       PRESIDENT            17-NOV-81       5000                    10
      7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30
      7876 ADAMS      CLERK           7788 23-MAY-87       1100                    20

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      7900 JAMES      CLERK           7698 03-DEC-81        950                    30
      7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
      7934 MILLER     CLERK           7782 23-JAN-82       1300                    10

14 rows selected.

更新一条数据:

SQL> update emp set ename='Rhys' where empno=7500;

1 row updated.
查看当前用户信息:

SQL> select sid,serial#,username from v$session where username='RHYS';

       SID    SERIAL# USERNAME
---------- ---------- ------------------------------
         1          7 RHYS

SQL>
session 2:

在另一个会话中转储redo file内容:
SQL> set linesize 200
SQL> col name for a60
SQL> alter system dump logfile '/opt/app/oracle/oradata/RHYS/redo01.log';
SQL> col value for a60
SQL> r
  1* 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_6532.trc

SQL>
session 3:

SQL> select addr,xidusn,xidslot,xidsqn,ubafil,ubablk,ubasqn,status from v$transaction;

select usn,latch,extents,rssize,xacts,gets,optsize,wraps,status from v$rollstat where xacts>0;

select * from v$rollname;
ADDR                 XIDUSN    XIDSLOT     XIDSQN     UBAFIL     UBABLK     UBASQN STATUS
---------------- ---------- ---------- ---------- ---------- ---------- ---------- ----------------
000000007BF283F0         20         31       4284          9      37599         91 ACTIVE

SQL> SQL>
       USN      LATCH    EXTENTS     RSSIZE      XACTS       GETS    OPTSIZE      WRAPS STATUS
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------
        20          0         32   20766720          1         27                     0 ONLINE

SQL> SQL>

       USN NAME
---------- ------------------------------
         0 SYSTEM
        11 _SYSSMU11_2531470812$
        12 _SYSSMU12_3537717698$
        13 _SYSSMU13_19894467$
        14 _SYSSMU14_4095940644$
        15 _SYSSMU15_452080806$
        16 _SYSSMU16_3613570610$
        17 _SYSSMU17_2475065771$
        18 _SYSSMU18_892025711$
        19 _SYSSMU19_927439322$
        20 _SYSSMU20_487181632$

11 rows selected.

SQL> alter system dump undo header "_SYSSMU20_487181632$";

System altered.

SQL> col value for a50
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_or
                                                                            a_6535.trc


SQL>
session 4:

SQL> set linesize 200
SQL> col name for a60
SQL> col value for a50
SQL> alter system dump datafile 9 block 37599;

System altered.

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_or
                                                                        a_6561.trc


SQL>

1)、查看redo record信息如下:
REDO RECORD - Thread:1 RBA: 0x00016c.0000000a.0010 LEN: 0x0218 VLD: 0x05
SCN: 0x0000.0050c823 SUBSCN:  1 10/24/2013 18:13:58
(LWN RBA: 0x00016c.0000000a.0010 LEN: 0002 NST: 0001 SCN: 0x0000.0050c823)

这是第一个改变向量:(change #1)

CHANGE #1 TYP:0 CLS:55 AFN:9 DBA:0x02400110 OBJ:4294967295 SCN:0x0000.0050c7ea SEQ:1 OP:5.2 ENC:0 RBL:0
ktudh redo: slt: 0x001f sqn: 0x000010bc flg: 0x000a siz: 160 fbi: 181
            uba: 0x024092df.005b.01    pxid:  0x0000.000.00000000
获得信息为afn:相对文件 号为9(undo 表空间数据文件号);slt为:1f正是undo事务槽号;op:5.2表示(Opcode 2 : Update rollback segment header - KTURDH),
sequence为:10bc也是undo的warp值:0x10bc,uba:前镜像地址为,24092df,顺序号为:005b,irb为:01,这指向了undo中的内容信息如下(在后边有记录):
###############################################################
  TRN TBL::
 
  index  state cflags  wrap#    uel         scn            dba            parent-xid    nub     stmt_num    cmt
  ------------------------------------------------------------------------------------------------
   0x1f   10    0x80  0x10bc  0x0013  0x0000.0050c823  0x024092df  0x0000.000.00000000  0x00000001   0x00000000  0
 
UNDO BLK: 
xid: 0x0014.01f.000010bc  seq: 0x5b  cnt: 0x1   irb: 0x1   icl: 0x0   flg: 0x0000
 
 Rec Offset      Rec Offset      Rec Offset      Rec Offset      Rec Offset
---------------------------------------------------------------------------
0x01 0x1f48    
################################################################
总结:这是第一步:首先要在undo空间中分配事务槽等信息:

CHANGE #2 TYP:1 CLS:56 AFN:9 DBA:0x024092df OBJ:4294967295 SCN:0x0000.0050c823 SEQ:1 OP:5.1 ENC:0 RBL:0
ktudb redo: siz: 160 spc: 0 flg: 0x000a seq: 0x005b rec: 0x01
            xid:  0x0014.01f.000010bc 
ktubl redo: slt: 31 rci: 0 opc: 11.1 [objn: 89179 objd: 89716 tsn: 8]
Undo type:  Regular undo        Begin trans    Last buffer split:  No
Temp Object:  No
Tablespace Undo:  No
             0x00000000  prev ctl uba: 0x024092de.005b.25
prev ctl max cmt scn:  0x0000.005072ce  prev tx cmt scn:  0x0000.0050730f
txn start scn:  0xffff.ffffffff  logon user: 92  prev brb: 37786328  prev bcl: 0 BuExt idx: 0 flg2: 0
KDO undo record:
KTB Redo
op: 0x03  ver: 0x01 
compat bit: 4 (post-11) padding: 1
op: Z
KDO Op code: URP row dependencies Disabled
  xtype: XA flags: 0x00000000  bdba: 0x01c0296e  hdba: 0x01c0296a
itli: 2  ispac: 0  maxfr: 4858
tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0
ncol: 8 nnew: 1 size: -1
col  1: [ 3]  41 4d 59
从第二个向量中可以获得的信息有:相对文件号为:9,数据的前镜像地址为dba:数据文件号为9,数据块为:37599,redo的操作码:op:5.1(Opcode 1 : Undo block or undo segment header - KTURDB),可以看到这里的事务号:xid:  0x0014.01f.000010bc获得回滚段为20事务槽位31wrap为10bc,后边记录的: slt: 31 rci: 0 opc: 11.1 [objn: 89179 objd: 89716 tsn: 8]表示:事务槽为31,rci为0说明这是在undo chain中最后一个的记录,对象变化为89179,数据对象变化为89716 tsn:为8,如下查询可知道正是我操作的这张表。另外登录的用户为rhys(通过92可知),然后在记录的就是前字段值为:41 4d 59转储为:AMY这正是原先字段值。如下是获得部分信息的查询操作:

SQL> col object_name for a50
SQL> r
  1*  select object_name,object_id,data_object_id,object_type from dba_objects where object_id=89179

OBJECT_NAME                                         OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE
-------------------------------------------------- ---------- -------------- -------------------
EMP                                                     89179          89716 TABLE

SQL> select * from v$tablespace;

       TS# NAME                           INC BIG FLA ENC
---------- ------------------------------ --- --- --- ---
         0 SYSTEM                         YES NO  YES
         1 SYSAUX                         YES NO  YES
         4 USERS                          YES NO  YES
         3 TEMP                           NO  NO  YES
         6 EXAMPLE                        YES NO  YES
         7 STATSPACK                      YES NO  YES
         8 RHYS                           YES NO  YES
         9 INDEX_TABLESPACE               YES NO  YES
        10 UNDOTBS02                      YES NO  YES

9 rows selected.
SQL> select username,user_id from dba_users where user_id=92;

USERNAME                          USER_ID
------------------------------ ----------
RHYS                                   92

SQL>
SQL> col value for a40
SQL> r
  1* select utl_raw.cast_to_varchar2(replace('41 4d 59',' ')) value from dual

VALUE
----------------------------------------
AMY

SQL>

这是第三个改变向量。

CHANGE #3 TYP:2 CLS:1 AFN:7 DBA:0x01c0296e OBJ:89716 SCN:0x0000.00505633 SEQ:1 OP:11.5 ENC:0 RBL:0
KTB Redo
op: 0x11  ver: 0x01 
compat bit: 4 (post-11) padding: 1
op: F  xid:  0x0014.01f.000010bc    uba: 0x024092df.005b.01
Block cleanout record, scn:  0x0000.0050c823 ver: 0x01 opt: 0x02, entries follow...
  itli: 1  flg: 2  scn: 0x0000.00505633
KDO Op code: URP row dependencies Disabled
  xtype: XA flags: 0x00000000  bdba: 0x01c0296e  hdba: 0x01c0296a
itli: 2  ispac: 0  maxfr: 4858
tabn: 0 slot: 0(0x0) flag: 0x2c lock: 2 ckix: 0
ncol: 8 nnew: 1 size: 1
col  1: [ 4]  52 68 79 73
其他的我就不说了,我们看一下这个值为:52 68 79 73 正是将表emp的empno为7500的ename改为Rhys。对了,注意这里还有一个bdba,代表修改块的前镜像:bdba:0x01c0296e 代表第七个数据文件的10606这个数据块。
这是第4个改变向量:

CHANGE #4 MEDIA RECOVERY MARKER SCN:0x0000.00000000 SEQ:0 OP:5.20 ENC:0
session number   = 1
serial  number   = 7
transaction name =
version 186647552
audit sessionid 7720329
Client Id =
login   username = RHYS
做了一个标记,MEDIA RECOVERY MARKER SCN:0x0000.00000000,但是没有提交,那么事务恢复的话就在此处了。可以看到sid为1,serial为7 还有audit正是session 1的用户信息:

2)查看undo信息如下:
。。。。。。
  TRN TBL::
 
  index  state cflags  wrap#    uel         scn            dba            parent-xid    nub     stmt_num    cmt
  ------------------------------------------------------------------------------------------------
   0x1f   10    0x80  0x10bc  0x0013  0x0000.0050c823  0x024092df  0x0000.000.00000000  0x00000001   0x00000000  0
   0x20    9    0x00  0x10bc  0x0002  0x0000.00507584  0x024092da  0x0000.000.00000000  0x00000001   0x00000000  1382608682
   0x21    9    0x00  0x10bc  0x001d  0x0000.0050764f  0x024092db  0x0000.000.00000000  0x00000001   0x00000000  1382608826
 。。。。。。。。
。。。。。。。。
********************************************************************************
********************************************************************************
Undo Segment:  _SYSSMU20_487181632$ (20)
********************************************************************************
  Extent Control Header
  -----------------------------------------------------------------
  Extent Header:: spare1: 0      spare2: 0      #extents: 32     #blocks: 2535 
                  last map  0x00000000  #maps: 0      offset: 4080 
      Highwater::  0x024092df  ext#: 19     blk#: 95     ext size: 128  
  #blocks in seg. hdr's freelists: 0    
  #blocks below: 0    
  mapblk  0x00000000  offset: 19   
                   Unlocked
     Map Header:: next  0x00000000  #extents: 32   obj#: 0      flag: 0x40000000
。。。。。。。。。。
UNDO BLK: 
xid: 0x0014.01f.000010bc  seq: 0x5b  cnt: 0x1   irb: 0x1   icl: 0x0   flg: 0x0000
 
 Rec Offset      Rec Offset      Rec Offset      Rec Offset      Rec Offset
---------------------------------------------------------------------------
0x01 0x1f48    
 
*-----------------------------
* Rec #0x1  slt: 0x1f  objn: 89179(0x00015c5b)  objd: 89716  tblspc: 8(0x00000008)
*       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: 0x024092de.005b.25 ctl max scn: 0x0000.005072ce prv tx scn: 0x0000.0050730f
txn start scn: scn: 0x0000.0050c823 logon user: 92
 prev brb: 37786328 prev bcl: 0
KDO undo record:
KTB Redo
op: 0x03  ver: 0x01 
compat bit: 4 (post-11) padding: 1
op: Z
KDO Op code: URP row dependencies Disabled
  xtype: XA flags: 0x00000000  bdba: 0x01c0296e  hdba: 0x01c0296a
itli: 2  ispac: 0  maxfr: 4858
tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0
ncol: 8 nnew: 1 size: -1
col  1: [ 3]  41 4d 59
 
End dump data blocks tsn: 10 file#: 9 minblk 37599 maxblk 37599
原镜像数据也是41 4d 59为amy

3)查看原镜像数据块如下:
。。。。。。。。。。。。。。。。。
Start dump data blocks tsn: 8 file#:7 minblk 10606 maxblk 10606
Block dump from cache:
Dump of buffer cache at level 4 for tsn=8 rdba=29370734
BH (0x777e2e10) file#: 7 rdba: 0x01c0296e (7/10606) class: 1 ba: 0x77554000
  set: 3 pool: 3 bsz: 8192 bsi: 0 sflg: 2 pwc: 0,0
  dbwrid: 0 obj: 89716 objn: 89179 tsn: 8 afn: 7 hint: f
  hash: [0x7c22e880,0x7c22e880] lru: [0x777e3038,0x777e2dc8]
  ckptq: [NULL] fileq: [NULL] objq: [0x777e3408,0x796cea90] objaq: [0x777e3418,0x796cea80]
  st: XCURRENT md: NULL fpin: 'kduwh01: kdusru' tch: 1
  flags: block_written_once redo_since_read
  LRBA: [0x0.0.0] LSCN: [0x0.0] HSCN: [0xffff.ffffffff] HSUB: [1]
Block dump from disk:
buffer tsn: 8 rdba: 0x01c0296e (7/10606)
scn: 0x0000.0050c823 seq: 0x01 flg: 0x04 tail: 0xc8230601
frmt: 0x02 chkval: 0x9ef8 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
。。。。。。。。。。。。。。。。。。。。
Block header dump:  0x01c0296e
 Object id on Block? Y
 seg/obj: 0x15e74  csc: 0x00.50c823  itc: 2  flg: E  typ: 1 - DATA
     brn: 0  bdba: 0x1c02968 ver: 0x01 opc: 0
     inc: 0  exflg: 0
 
 Itl           Xid                  Uba         Flag  Lck        Scn/Fsc
0x01   0x0014.017.00001085  0x024092b6.005b.01  C---    0  scn 0x0000.00505633
0x02   0x0014.01f.000010bc  0x024092df.005b.01  ----    1  fsc 0x0000.00000000
bdba: 0x01c0296e

note:bdba,xid这和前面的一致
另外注意这个flag:
Flag – Transaction flag
----         = Uncommitted
-B--        = The UBA (Undo Block Address) contains undo for this ITL
--U-        = Committed by fast commits & delayed block cleanout has not occurred
---T        = Transaction active at block cleanout SCN
-C-U- = Block cleaned by delayed block cleanout, and rollback segment info is    overwritten.

。。。。。。。。。。。
block_row_dump:
tab 0, row 0, @0x1d42
tl: 36 fb: --H-FL-- lb: 0x2  cc: 8
col  0: [ 2]  c2 4c
col  1: [ 4]  52 68 79 73
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, @0x1d89
注意:这里的lb代表锁定状态正是指向了itl为0x02。
总结一下:

当我更新一条数据的时候,

1、首次查看该数据是否在buffer cache中,如果没有则从数据文件读入buffer cache

2、更新操作时首先在undo分配事务槽,并记录redo信息

2、在buffer cache中创建数据的前镜像,并记录redo信息

3、修改值,需要记录redo信息

4、提交之后再redo中记录信息,并标记undo中的数据为非激活状态,flag标记进行相应改变。

 

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