10g Super Block and Bootstrap$

Environment:

Oracle 10.0.2.1.0

Linux kernal 2.6.18-92.el5PAE

ASSM Tablespace

Important: 9i and 10g's root dba are different

FILE HEADER:

status:0x4 root dba: 0x004001a1 chkpt cnt: 75 ctl cnt:74 --9i point to a cache block, cache block point to bootstrap$

FILE HEADER:

  status:0x4 root dba: 0x00400179 chkpt cnt: 75 ctl cnt:74 --10g direct point to bootstrap$, this object is no more cached, that's the why database can't be started when SYSTEM tablespace corrupted

Introduction

Each Oracle database has a SYSTEM tablespace, and each SYSTEM tablespace has a Super Block which is file 1 block 1, the Super Block has it's struct KCVFH 676 bytes(10g)

struct kcvfh {

kcbh kcvfhbfh;    -- Block Header, like every single block, 20bytes

kccfhg kcvfhhdr;

krdba kcvfhrdb;   -- point ot bootstrap$ RDBA address, ONLY exist in FILE#1

kscn kcvfhcrs;    -- SCN when datafile created

ub4 kcvfhcrt;     --Timestamp when datafile created

………}

Bootstrap$ including those main system dictionary, such as OBJ$, and segment HDR address

What is Bootstrap: Bootstrap is a technique for loading the first few instructions of a computer program into active memory and then using them to bring in the rest of the program.

What is Bootstrap in Oracle: In Oracle, Bootstrap refers to loading of metadata (data dictionary) before we OPEN the database. Bootstrap objects are classified as the objects (tables / indexes / clusters) with the object_id below 56 as bootstrap objects. These objects are mandatory to bring up an instance, as this contains the most important metadata of the database.

After all, before analysis Oracle database structure, we need to use Super Block to find the position of Bootstrap$, through Bootstrap$ we can find those main system dictionaries, such as OBJ$, C_OBJ$, TAB$, COL$, etc…

 

Bootstrap$ is created by script $ORACLE_HOME/RMDBS/ADMIN/sql.bsq, the position of this script is defined by a Hidden Parameter _init_sql_file

SQL> @ GetHiddenParameter.sql

Enter value for par: init_sql_file

old   8:  where x.inst_id = userenv('Instance') and y.inst_id = userenv('Instance') and x.indx = y.indx and x.ksppinm like '%_&par%'

new   8:  where x.inst_id = userenv('Instance') and y.inst_id = userenv('Instance') and x.indx = y.indx and x.ksppinm like '%_init_sql_file%'

NAME        VALUE                ISDEFAULT  ISMOD      ISADJ

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

_init_sql_file   ?/rdbms/admin/sql.bsq  TRUE       FALSE      FALSE

 

Before sql.bsq  there is another script $ORACLE_HOME/RMDBS/ADMIN/CreateDB.sql which called to create Bootstrap$

 

Started to analysis 1) Super Block (set dba 1,1) -> kcvfhrdb -> Dump File# 1 Block# 377; 2) Trace Oracle database startup process

 

1) Super Block (set dba 1,1) -> kcvfhrdb -> Dump File# 1 Block# 377

BBED> set dba 1,1

       DBA             0x00400001 (4194305 1,1)

 

BBED> map /v

File: /u01/app/oracle/oradata/orcl/system01.dbf (1)

Block: 1                                     Dba:0x00400001

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

Data File Header

 

struct kcvfh, 676 bytes                    @0      

    struct kcvfhbfh, 20 bytes               @0      

    struct kcvfhhdr, 76 bytes               @20     

     ub4 kcvfhrdb                            @96     

    struct kcvfhcrs, 8 bytes                @100    

    ub4 kcvfhcrt                            @108    

    ub4 kcvfhrlc                            @112    

    struct kcvfhrls, 8 bytes                @116    

    ub4 kcvfhbti                            @124    

    struct kcvfhbsc, 8 bytes                @128    

    ub2 kcvfhbth                            @136    

    ub2 kcvfhsta                            @138    

    struct kcvfhckp, 36 bytes               @484    

    ub4 kcvfhcpc                            @140    

    ub4 kcvfhrts                            @144    

    ub4 kcvfhccc                            @148    

    struct kcvfhbcp, 36 bytes               @152    

    ub4 kcvfhbhz                            @312    

    struct kcvfhxcd, 16 bytes               @316    

    word kcvfhtsn                           @332    

    ub2 kcvfhtln                            @336    

    text kcvfhtnm[30]                       @338    

    ub4 kcvfhrfn                            @368    

    struct kcvfhrfs, 8 bytes                @372    

    ub4 kcvfhrft                            @380    

    struct kcvfhafs, 8 bytes                @384    

    ub4 kcvfhbbc                            @392    

    ub4 kcvfhncb                            @396    

    ub4 kcvfhmcb                            @400    

    ub4 kcvfhlcb                            @404    

    ub4 kcvfhbcs                            @408    

    ub2 kcvfhofb                            @412    

    ub2 kcvfhnfb                            @414    

    ub4 kcvfhprc                            @416    

    struct kcvfhprs, 8 bytes                @420    

    struct kcvfhprfs, 8 bytes               @428    

    ub4 kcvfhtrt                            @444    

 

ub4 tailchk                                @8188   

 

BBED> print kcvfhrdb

ub4 kcvfhrdb                                @96        0x00400179

 

SQL> select dbms_utility . DATA_BLOCK_ADDRESS_FILE ( to_number ( '400179' , 'xxxxxxxxxx' )) file# ,

      dbms_utility . DATA_BLOCK_ADDRESS_BLOCK ( to_number ( '400179' , 'xxxxxxxxxx' )) block#

     from dual;

     FILE#  BLOCK#

----------  ----------

       1      377

 

SQL> select segment_name,file_id,block_id from dba_extents where block_id=377;

 

SEGMENT_NAME                                                                         FILE_ID   BLOCK_ID

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

BOOTSTRAP$                                                                                 1        377

I_DIR$INSTANCE_JOB_NAME                                                                    3        377

SYS_C005392                                                                                4        377

PRODUCT_INFORMATION                                                                        5        377

 

SQL> alter system dump datafile 1 block 377;

 

System altered.

 

Start dump data blocks tsn: 0 file#: 1 minblk 377 maxblk 377

buffer tsn: 0 rdba: 0x00400179 (1/377)

scn: 0x0000.0000014e seq: 0x01 flg: 0x04 tail: 0x014e1001

frmt: 0x02 chkval: 0xe733 type: 0x10=DATA SEGMENT HEADER - UNLIMITED

Hex dump of block: st=0, typ_found=1

Dump of memory from 0x0DCE4400 to 0x0DCE6400

<---- More ----> >

Extent Control Header

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

Extent Header:: spare1: 0      spare2: 0      #extents: 1      #blocks: 7    

                  last map  0x00000000  #maps: 0      offset: 4128 

      Highwater::  0x0040017d  ext#: 0      blk#: 3      ext size: 7    

  #blocks in seg. hdr's freelists: 1    

  #blocks below: 3    

  mapblk  0x00000000  offset: 0    

                   Unlocked

    Map Header:: next  0x00000000  #extents: 1     obj#: 56     flag: 0x40000000

Extent Map

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

  0x0040017a  length: 7    

 

  nfl = 1, nfb = 1 typ = 1 nxf = 0 ccnt = 3

SEG LST:: flg: USED   lhd: 0x0040017c ltl: 0x0040017c

End dump data blocks tsn: 0 file#: 1 minblk 377 maxblk 377

 

SQL> select name from sys.obj$ where obj#=56;

 

NAME

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

BOOTSTRAP$

 

SQL> desc sys.bootstrap$

 

Name       Null?    Type

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

LINE#       NOT NULL NUMBER

OBJ#       NOT NULL NUMBER

SQL_TEXT   NOT NULL VARCHAR2(4000)

 

SQL> select * from sys.bootstrap$;

LINE#  OBJ#   SQL_TEXT

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

   -1    -1    8.0.0.0.0

   0     0    CREATE ROLLBACK SEGMENT SYSTEM STORAGE (  INITIAL 112K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 32765 OBJNO 0 EXTENTS (FILE 1 BLOCK 9))

…………………

53    53    CREATE INDEX I_CDEF4 ON CDEF$(ENABLED) PCTFREE 10 INITRANS 2 MAXTRANS 255 STORAGE (  INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJNO 53 EXTENTS (FILE 1 BLOCK 353))

57 rows selected.

 

2) Trace Oracle database startup process & 10046 events

先通过 direct path read 从每个数据文件头读取第一个 Block 信息 , 然后通过 db file sequential read 的单块读方式分别读取了数据文件 1 的 417 和 377block, 417 上放着 1.417 号对象 , 从而找到bootstrap$ 对象 , 找到了 377, 并且在内存中建立了这个对象

shutdown immediate

startup mount ;

alter session set sql_trace = true ;

alter database open ;

alter database open

END OF STMT

PARSE #1:c=3000,e=2948,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=1,tim=1245077587182259

tkcrrsarc: (WARN) Failed to find ARCH for message (message:0x1)

tkcrrpa: (WARN) Failed initial attempt to send ARCH message (message:0x1)

=====================

PARSING IN CURSOR #2 len=188 dep=1 uid=0 oct=1 lid=0 tim=1245077587762182 hv=1365064427 ad='4174f3ec'

create table bootstrap$ ( line# number not null,obj# number not null, 

                          sql_text varchar2(4000) not null)

                          storage (initial 50K objno 56 extents (file 1 block 377))

=====================

PARSING IN CURSOR #2 len=55 dep=1 uid=0 oct=3 lid=0 tim=1245077587770912 hv=2111436465 ad='4174ec78'

select line#, sql_text from bootstrap$ where obj# != :1

END OF STMT

PARSE #2:c=4999,e=4673,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,tim=1245077587770907

EXEC #2:c=7999,e=7697,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,tim=1245077587778793

FETCH #2:c=6999,e=6763,p=4,cr=3,cu=0,mis=0,r=1,dep=1,og=4,tim=1245077587785627

 

关于 bootstrap$ 定位由 System 表空间的文件头的 root dba 数据结构来定位的

FILE HEADER:

status:0x4 root dba:0x004001a1 chkpt cnt: 75 ctl cnt:74 --9i

FILE HEADER:

status:0x4 root dba: 0x00400179 chkpt cnt: 75 ctl cnt:74 --10g 直接指向了 bootstrap$ 从而取消了 Cache 这个唯一对象 , 这就是为什么 system 坏了就完了

 

select * from dba_segments where header_file = 1 and header_block = 417; --10g 已经查不到 type 是 cache 了

 

在数据库 bootstrap 过程中所有文件 1 的 417 以及之前所有对象都需要来 bootstrap

select b . object_id , a . segment_name , a . segment_type , a . header_block

   from dba_segments a , dba_objects b

  where a . segment_name = b . object_name (+) and a . header_file = 1 and a . header_block <= 417

  order by a . header_block; --10g 已经没有 1.417 这个对象了

 

alter system dump datafile 1 block 417 ;

Start dump data blocks tsn: 0 file#: 1 minblk 417 maxblk 417

buffer tsn: 0 rdba: 0x004001a1 (1/417)

scn: 0x0000.0005f26d seq: 0x01 flg: 0x04 tail: 0xf26d1001

frmt: 0x02 chkval: 0x264f type: 0x10=DATA SEGMENT HEADER - UNLIMITED

Hex dump of block: st=0, typ_found=1

Dump of memory from 0x0DBF2400 to 0x0DBF4400

AA84E40               00400179 [y.@.] -- 这个传说中 9i 中有的 10g 中没有了的这个 377 的指向

 

--EOF--