替换bootstarp$表

发表于 2013 年 12 月 15 日 由 惜分飞

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标题：替换bootstarp$表

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

对数据库有一定了解的人都知道，数据库启动是通过bootstarp$表来实现启动引导的。那这里有两个疑问：
1.引导表bootstarp$名字是否是唯一？
2.引导表的位置是不是在数据文件固定？比如11g/12c在file 1 block 520，10g在file 1 block 377？

跟踪数据库启动

[oracle@rac2 ~]$ sqlplus / as sysdba

SQL*Plus: Release 12.1.0.1.0 Production on Sun Dec 15 14:16:58 2013

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Advanced Analytics
and Real Application Testing options

SQL> startup mount;
ORACLE instance started.

Total System Global Area  400846848 bytes
Fixed Size                  2288872 bytes
Variable Size             310379288 bytes
Database Buffers           79691776 bytes
Redo Buffers                8486912 bytes
Database mounted.
SQL> oradebug setmypid
Statement processed.
SQL> alter session set db_file_multiblocK_read_count=1;
Statement processed.
SQL> oradebug EVENT 10046 TRACE NAME CONTEXT FOREVER, LEVEL 12
Session altered.
SQL> oradebug TRACEFILE_NAME
/u01/app/oracle/diag/rdbms/test/TEST/trace/TEST_ora_31364.trc
SQL> alter database Open;

Database altered.
SQL> oradebug EVENT 10046 trace name context off
Statement processed.

SQL> select HEADER_FILE,HEADER_BLOCK from dba_segments where segment_name='BOOTSTRAP$';

HEADER_FILE HEADER_BLOCK
----------- ------------
          1          520

SQL> select object_id from dba_objects where object_name='BOOTSTRAP$';

 OBJECT_ID
----------
        59

分析trace文件

WAIT #140077386411120: nam='db file sequential read' ela= 56 file#=1 block#=520 blocks=1 obj#=-1 tim=1719385755334
=====================
PARSING IN CURSOR #140077386402760 len=188 dep=1 uid=0 oct=1 lid=0 tim=1719385757322 hv=4006182593 ad='6645d370' sqlid='32r4f1brckzq1'
create table bootstrap$ (
END OF STMT
PARSE #140077386402760:c=2000,e=1711,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,plh=0,tim=1719385757319
EXEC #140077386402760:c=0,e=430,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,plh=0,tim=1719385757909
CLOSE #140077386402760:c=0,e=9,dep=1,type=0,tim=1719385758105
=====================
PARSING IN CURSOR #140077386402760 len=55 dep=1 uid=0 oct=3 lid=0 tim=1719385759507 hv=2111436465 ad='6645bc80' sqlid='6apq2rjyxmxpj'
select line#, sql_text from bootstrap$ where obj# != :1
END OF STMT
PARSE #140077386402760:c=1000,e=1365,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,plh=0,tim=1719385759505
BINDS #140077386402760:
 Bind#0
  oacdty=02 mxl=22(22) mxlc=00 mal=00 scl=00 pre=00
  oacflg=08 fl2=1000001 frm=00 csi=00 siz=24 off=0
  kxsbbbfp=7f664edb8780  bln=22  avl=02  flg=05
  value=59
EXEC #140077386402760:c=3000,e=8859,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,plh=867914364,tim=1719385768574
WAIT #140077386402760: nam='db file sequential read' ela= 27 file#=1 block#=520 blocks=1 obj#=59 tim=1719385768753
WAIT #140077386402760: nam='db file sequential read' ela= 23 file#=1 block#=521 blocks=1 obj#=59 tim=1719385769575

这里我们可以发现，数据库启动的时候是读file 1 block 520，object_id为59，为bootstarp$对象

bbed查看root rdba地址

ub4 kcvfhrdb                             @96       0x00400208

SQL> select to_number('208','xxx') from dual;

TO_NUMBER('208','XXX')
----------------------
                   520

这里可以看出来，数据库启动的file header rdba地址和trace文件中的一致，也是指定到bootstarp$;

替换bootstrap$表为xifenfei

SQL> create table xifenfei as select * from bootstrap$;

Table created.

SQL> desc xifenfei
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 LINE#                                     NOT NULL NUMBER
 OBJ#                                      NOT NULL NUMBER
 SQL_TEXT                                  NOT NULL VARCHAR2(4000)

SQL> select sql_text from xifenfei where line#=59;

SQL_TEXT
--------------------------------------------------------------------------------
CREATE TABLE BOOTSTRAP$("LINE#" NUMBER NOT NULL,"OBJ#" NUMBER NOT NULL,"SQL_TEXT
" VARCHAR2(4000) NOT NULL) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 STORAGE
 (  INITIAL 56K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJN
O 59 EXTENTS (FILE 1 BLOCK 520))

--清除bootstarp$记录
SQL> delete from xifenfei where line#=59;

1 row deleted.

SQL> commit;

Commit complete.

SQL> select objECT_ID from dba_objects where object_name='XIFENFEI';

 OBJECT_ID
----------
     20314

SQL> select HEADER_FILE,HEADER_BLOCK from dba_segments where segment_name='XIFENFEI';

HEADER_FILE HEADER_BLOCK
----------- ------------
          1        45712


SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup upgrade;
ORACLE instance started.

Total System Global Area  400846848 bytes
Fixed Size                  2288872 bytes
Variable Size             310379288 bytes
Database Buffers           79691776 bytes
Redo Buffers                8486912 bytes
Database mounted.
Database opened.

--删除bootstarp$表
SQL>  drop table bootstrap$;

Table dropped.

SQL>  exec DBMS_DDL_INTERNAL.SWAP_BOOTSTRAP('XIFENFEI');

PL/SQL procedure successfully completed.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> EXIT
Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Advanced Analytics
and Real Application Testing options
[oracle@rac2 ~]$ sqlplus / as sysdba

SQL*Plus: Release 12.1.0.1.0 Production on Sun Dec 15 14:29:54 2013

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> STARTUP MOUNT
ORACLE instance started.

Total System Global Area  400846848 bytes
Fixed Size                  2288872 bytes
Variable Size             310379288 bytes
Database Buffers           79691776 bytes
Redo Buffers                8486912 bytes
Database mounted.
SQL> oradebug setmypid
Statement processed.
SQL> oradebug EVENT 10046 TRACE NAME CONTEXT FOREVER, LEVEL 12
Statement processed.
SQL> alter session set db_file_multiblocK_read_count=1;

Session altered.

SQL> oradebug TRACEFILE_NAME
/u01/app/oracle/diag/rdbms/test/TEST/trace/TEST_ora_32727.trc
SQL> alter database Open;

Database altered.

SQL> SELECT OBJECT_ID FROM DBA_OBJECTS WHERE OBJECT_NAME='BOOTSTRAP$';

no rows selected

SQL> SELECT OBJECT_ID FROM DBA_OBJECTS WHERE OBJECT_NAME='XIFENFEI'; 

 OBJECT_ID
----------
     20314

分析trace文件

WAIT #139841534602352: nam='db file sequential read' ela= 23 file#=1 block#=45712 blocks=1 obj#=-1 tim=1720082484775
=====================
PARSING IN CURSOR #139841534593992 len=193 dep=1 uid=0 oct=1 lid=0 tim=1720082488552 hv=2096904950 ad='6645d650' sqlid='bs6v55xygsfrq'
create table bootstrap$ (
END OF STMT
PARSE #139841534593992:c=2000,e=2925,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,plh=0,tim=1720082488550
EXEC #139841534593992:c=0,e=466,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,plh=0,tim=1720082489124
CLOSE #139841534593992:c=0,e=8,dep=1,type=0,tim=1720082489266
=====================
PARSING IN CURSOR #139841534593992 len=55 dep=1 uid=0 oct=3 lid=0 tim=1720082490510 hv=2111436465 ad='6645c050' sqlid='6apq2rjyxmxpj'
select line#, sql_text from bootstrap$ where obj# != :1
END OF STMT
PARSE #139841534593992:c=1999,e=1211,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,plh=0,tim=1720082490509
BINDS #139841534593992:
 Bind#0
  oacdty=02 mxl=22(22) mxlc=00 mal=00 scl=00 pre=00
  oacflg=08 fl2=1000001 frm=00 csi=00 siz=24 off=0
  kxsbbbfp=7f2f64fe8780  bln=22  avl=04  flg=05
  value=20314
EXEC #139841534593992:c=1000,e=1789,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,plh=867914364,tim=1720082492533
WAIT #139841534593992: nam='db file sequential read' ela= 20 file#=1 block#=45712 blocks=1 obj#=20314 tim=1720082492685
WAIT #139841534593992: nam='db file sequential read' ela= 25 file#=1 block#=45713 blocks=1 obj#=20314 tim=1720082492986

这里可以看出来，数据库在启动的时候是读取file 1 block 45712，object_id为20314

bbed查看root rdba地址

ub4 kcvfhrdb                             @96       0x0040b290

SQL> select to_number('b290','xxxxxxx') from dual;

TO_NUMBER('B290','XXXXXXX')
---------------------------
                      45712

证明现在的文件头里面的file header rdba 已经修改为file 1 block 45712和trace里面看到的一致,都是XIFENFEI这个表

测试结论
1. 通过使用SWAP_BOOTSTRAP可以置换掉数据库启动开始表bootstrap$变为另外一个表,而且该过程直接修改文件头的kcvfhrdb值
2. 通过试验证明,oracle启动的时候不是程序里面写死的去读file 1的某个block,而是通过读取kcvfhrdb然后启动数据库

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《替换bootstarp$表》有 2 条评论

  1. desert_xu 说：
    2016 年 2 月 17 日10:52

    问一个问题，同一版本下 bootstrap$ 表内容是不是一样的？换句话说该bootstrap$ 有问题，是否可以用其他的库的bootstrap$ 替换，通过dd 命令拷贝复制到有问题的bootstrap$里？

  2. 惜分飞 说：
    2013 年 12 月 15 日17:19

    非默认的bootstarp$表位置,dul依然能够识别，证明dul是根据kcvfhrdb来寻找bootstarp$表

    [root@rac2 DUL]# ./dul

Data UnLoader: 10.2.0.5.25 - Internal Only - on Sun Dec 15 17:17:40 2013
with 64-bit io functions

Copyright (c) 1994 2013 Bernard van Duijnen All rights reserved.

 Strictly Oracle Internal Use Only


Found db_id = 2130779811
Found db_name = TEST
DUL> bootstrap;
Probing file = 1, block = 45712
. unloading table                BOOTSTRAP$
DUL: Warning: block number is non zero but marked deferred trying to process it anyhow
      59 rows unloaded
DUL: Warning: Dictionary cache DC_BOOTSTRAP is empty
Reading BOOTSTRAP.dat 59 entries loaded
Parsing Bootstrap$ contents
Generating dict.ddl for version 10
 OBJ$: segobjno 18, file 1 block 240
 TAB$: segobjno 2, tabno 1, file 1  block 144
 COL$: segobjno 2, tabno 5, file 1  block 144
 USER$: segobjno 10, tabno 1, file 1  block 208