SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 131142648 bytes
Fixed Size 451576 bytes
Variable Size 104857600 bytes
Database Buffers 25165824 bytes
Redo Buffers 667648 bytes
Database mounted.
SQL> alter session set sql_trace = true;
Session altered.
SQL> alter database open;
Database altered.
SQL>
首先我們來參考跟蹤文件的前部分(參考附件)
這是第一個對象的創建
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))
接下來我們來看執行的是
select line#, sql_text
from
bootstrap$ where obj# != :1
(這裏實際上是逐步提取內容建立字典表本身的結構,根據後面內容可知)
那麼在這裏我們在數據庫中來看看 bootstap$
SQL> desc bootstrap$
Name Null? Type
----------------------------------------- -------- ----------------------------
LINE# NOT NULL NUMBER
OBJ# NOT NULL NUMBER
SQL_TEXT NOT NULL VARCHAR2(4000)
SQL>
SQL> select count(*) from bootstrap$;
57
SQL>
SQL> select obj#,sql_text from bootstrap$ where rownum<11;
-1
8.0.0.0.0
0
CREATE ROLLBACK SEGMENT SYSTEM STORAGE ( INITIAL 112K NEXT 1024K MINEXTENTS 1 M
AXEXTENTS 32765 OBJNO 0 EXTENTS (FILE 1 BLOCK 9))
8
CREATE CLUSTER C_FILE#_BLOCK#("TS#" NUMBER,"SEGFILE#" NUMBER,"SEGBLOCK#" NUMBER)
PCTFREE 10 PCTUSED 40 INITRANS 2 MAXTRANS 255 STORAGE ( INITIAL 24K NEXT 1024K
MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJNO 8 EXTENTS (FILE 1 BLOCK
73)) SIZE 225
9
CREATE INDEX I_FILE#_BLOCK# ON CLUSTER C_FILE#_BLOCK# PCTFREE 10 INITRANS 2 MAXT
RANS 255 STORAGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PC
TINCREASE 0 OBJNO 9 EXTENTS (FILE 1 BLOCK 81))
14
CREATE TABLE SEG$("FILE#" NUMBER NOT NULL,"BLOCK#" NUMBER NOT NULL,"TYPE#" NUMBE
R NOT NULL,"TS#" NUMBER NOT NULL,"BLOCKS" NUMBER NOT NULL,"EXTENTS" NUMBER NOT N
ULL,"INIEXTS" NUMBER NOT NULL,"MINEXTS" NUMBER NOT NULL,"MAXEXTS" NUMBER NOT NUL
L,"EXTSIZE" NUMBER NOT NULL,"EXTPCT" NUMBER NOT NULL,"USER#" NUMBER NOT NULL,"LI
STS" NUMBER,"GROUPS" NUMBER,"BITMAPRANGES" NUMBER NOT NULL,"CACHEHINT" NUMBER NO
T NULL,"SCANHINT" NUMBER NOT NULL,"HWMINCR" NUMBER NOT NULL,"SPARE1" NUMBER,"SPA
RE2" NUMBER) STORAGE ( OBJNO 14 TABNO 2) CLUSTER C_FILE#_BLOCK#(TS#,FILE#,BLOCK
#)
5
CREATE TABLE CLU$("OBJ#" NUMBER NOT NULL,"DATAOBJ#" NUMBER,"TS#" NUMBER NOT NULL
,"FILE#" NUMBER NOT NULL,"BLOCK#" NUMBER NOT NULL,"COLS" NUMBER NOT NULL,"PCTFRE
E$" NUMBER NOT NULL,"PCTUSED$" NUMBER NOT NULL,"INITRANS" NUMBER NOT NULL,"MAXTR
ANS" NUMBER NOT NULL,"SIZE$" NUMBER,"HASHFUNC" VARCHAR2(30),"HASHKEYS" NUMBER,"F
UNC" NUMBER,"EXTIND" NUMBER,"FLAGS" NUMBER,"DEGREE" NUMBER,"INSTANCES" NUMBER,"A
VGCHN" NUMBER,"SPARE1" NUMBER,"SPARE2" NUMBER,"SPARE3" NUMBER,"SPARE4" NUMBER,"S
PARE5" VARCHAR2(1000),"SPARE6" VARCHAR2(1000),"SPARE7" DATE) STORAGE ( OBJNO 5
TABNO 2) CLUSTER C_OBJ#(OBJ#)
6
CREATE CLUSTER C_TS#("TS#" NUMBER) PCTFREE 10 PCTUSED 40 INITRANS 2 MAXTRANS 255
STORAGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREAS
E 0 OBJNO 6 EXTENTS (FILE 1 BLOCK 57))
7
CREATE INDEX I_TS# ON CLUSTER C_TS# PCTFREE 10 INITRANS 2 MAXTRANS 255 STORAGE (
INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJNO
7 EXTENTS (FILE 1 BLOCK 65))
18
CREATE TABLE OBJ$("OBJ#" NUMBER NOT NULL,"DATAOBJ#" NUMBER,"OWNER#" NUMBER NOT N
ULL,"NAME" VARCHAR2(30) NOT NULL,"NAMESPACE" NUMBER NOT NULL,"SUBNAME" VARCHAR2(
30),"TYPE#" NUMBER NOT NULL,"CTIME" DATE NOT NULL,"MTIME" DATE NOT NULL,"STIME"
DATE NOT NULL,"STATUS" NUMBER NOT NULL,"REMOTEOWNER" VARCHAR2(30),"LINKNAME" VAR
CHAR2(128),"FLAGS" NUMBER,"OID$" RAW(16),"SPARE1" NUMBER,"SPARE2" NUMBER,"SPARE3
" NUMBER,"SPARE4" VARCHAR2(1000),"SPARE5" VARCHAR2(1000),"SPARE6" DATE) PCTFREE
10 PCTUSED 40 INITRANS 1 MAXTRANS 255 STORAGE ( INITIAL 16K NEXT 1024K MINEXTEN
TS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJNO 18 EXTENTS (FILE 1 BLOCK 121))
36
CREATE UNIQUE INDEX I_OBJ1 ON OBJ$(OBJ#) PCTFREE 10 INITRANS 2 MAXTRANS 255 STOR
AGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 O
BJNO 36 EXTENTS (FILE 1 BLOCK 217))
10 rows selected.
SQL>
由這裏我們可以看出，bootstrap$ 中實際上是記錄了一些數據庫系統基本對象的創建語句
那對於我們數據庫來說，也可以看做建立一個表結構，通過這個結構可以通過關係型數據庫的方式去獲取文件中數據
ok,接下來我們看看trace文件中的內容，發現
CREATE ROLLBACK SEGMENT SYSTEM STORAGE ( INITIAL 112K NEXT 1024K MINEXTENTS
1 MAXEXTENTS 32765 OBJNO 0 EXTENTS (FILE 1 BLOCK 9))
在數據庫系統表空間的頭部創建了系統回滾段（block 9 開始，1---8 屬於數據文件頭）
再往下
CREATE CLUSTER C_OBJ#("OBJ#" NUMBER) PCTFREE 5 PCTUSED 40 INITRANS 2 MAXTRANS
255 STORAGE ( INITIAL 136K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 OBJNO 2 EXTENTS (FILE 1 BLOCK 25)) SIZE 800
這裏同樣是直接指定了該cluster 的段頭位置 block 25
SQL> select file_id,block_id from dba_extents where segment_name = 'C_OBJ#';
1 25
1 33
1 41
1 3241
1 4441
1 4473
1 4489
1 4513
1 4529
1 4561
1 4585
1 4609
1 4641
1 4681
1 4753
1 4833
1 4873
1 12681
1 23689
1 26249
20 rows selected.
CREATE INDEX I_OBJ# ON CLUSTER C_OBJ# PCTFREE 10 INITRANS 2 MAXTRANS 255
STORAGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 OBJNO 3 EXTENTS (FILE 1 BLOCK 49))
CREATE TABLE TAB$("OBJ#" NUMBER NOT NULL,"DATAOBJ#" NUMBER,"TS#" NUMBER NOT
NULL,"FILE#" NUMBER NOT NULL,"BLOCK#" NUMBER NOT NULL,"BOBJ#" NUMBER,"TAB#"
NUMBER,"COLS" NUMBER NOT NULL,"CLUCOLS" NUMBER,"PCTFREE$" NUMBER NOT NULL,
"PCTUSED$" NUMBER NOT NULL,"INITRANS" NUMBER NOT NULL,"MAXTRANS" NUMBER NOT
NULL,"FLAGS" NUMBER NOT NULL,"AUDIT$" VARCHAR2(38) NOT NULL,"ROWCNT" NUMBER,
"BLKCNT" NUMBER,"EMPCNT" NUMBER,"AVGSPC" NUMBER,"CHNCNT" NUMBER,"AVGRLN"
NUMBER,"AVGSPC_FLB" NUMBER,"FLBCNT" NUMBER,"ANALYZETIME" DATE,"SAMPLESIZE"
NUMBER,"DEGREE" NUMBER,"INSTANCES" NUMBER,"INTCOLS" NUMBER NOT NULL,
"KERNELCOLS" NUMBER NOT NULL,"PROPERTY" NUMBER NOT NULL,"TRIGFLAG" NUMBER,
"SPARE1" NUMBER,"SPARE2" NUMBER,"SPARE3" NUMBER,"SPARE4" VARCHAR2(1000),
"SPARE5" VARCHAR2(1000),"SPARE6" DATE) STORAGE ( OBJNO 4 TABNO 1) CLUSTER
C_OBJ#(OBJ#)
我們可以看到，從tab$ 開始，存儲發生了變化，
STORAGE ( OBJNO 4 TABNO 1) CLUSTER C_OBJ#(OBJ#)
那這裏的 objno 4 tabno 1 表示什麼意思呢?(通過 cluster C_OBJ#(OBJ#)我們就可以找到表tab$自身)
SQL> select * from tab$ where obj# = 4 and tab# = 1;
OBJ# DATAOBJ# TS# FILE# BLOCK# BOBJ# TAB#
---------- ---------- ---------- ---------- ---------- ---------- ----------
COLS CLUCOLS PCTFREE$ PCTUSED$ INITRANS MAXTRANS FLAGS
---------- ---------- ---------- ---------- ---------- ---------- ----------
AUDIT$ ROWCNT BLKCNT EMPCNT
-------------------------------------- ---------- ---------- ----------
AVGSPC CHNCNT AVGRLN AVGSPC_FLB FLBCNT ANALYZETI SAMPLESIZE
---------- ---------- ---------- ---------- ---------- --------- ----------
DEGREE INSTANCES INTCOLS KERNELCOLS PROPERTY TRIGFLAG SPARE1
---------- ---------- ---------- ---------- ---------- ---------- ----------
SPARE2 SPARE3
---------- ----------
SPARE4
--------------------------------------------------------------------------------
SPARE5
--------------------------------------------------------------------------------
SPARE6
---------
4 2 0 1 25 2 1
37 1 0 0 0 0 17
-------------------------------- 921 428 83
2381 0 139 6368 7 11-AUG-03 921
37 37 1024 0 0
06-AUG-03
SQL>
由這裏可以看出，存儲參數從這裏開始，就從數據文件中固定表的記錄中取出來
由此再往trace文件看下去，就會發現這個時候數據庫已經可以通過已有信息從系統表空間文件中提取結構信息和數據信息
我們看上面關於存儲的定義
CREATE CLUSTER C_OBJ#("OBJ#" NUMBER) PCTFREE 5 PCTUSED 40 INITRANS 2 MAXTRANS
255 STORAGE ( INITIAL 136K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 OBJNO 2 EXTENTS (FILE 1 BLOCK 25)) SIZE 800
這裏的extents 指明瞭是 block 25,我們假設在初始化參數文件中db_block_size設置不當，則必然導致文件位置定位錯誤
之所以要來研究這個問題（以前研究了今天寫出來而已），是因爲最早思考這樣一個問題
我們要查詢自己系統的一個表，則首先是去數據字典中找到該表的結構性信息
這些結構性信息存儲在數據字典表中，但我們又從哪裏獲得數據字典表本身的結構性信息呢？
雖然從表中我們可以查詢到字典表本身的結構性信息，那在數據庫open的時候最初是如何確定結構的？
是寫死在程序中呢？還是怎樣處理的
由上面內容我們可以看出，程序中只要提供 bootstrap$ 的創建腳本，確定好bootstap$的結構同時指定了段頭的位置
然後就能通過段頭去獲取bootstrap$中的內容，而這些內容就是爲一些字典表創建結構的sql_text
這樣就因了bootstrap$這個天生的蛋，孵化出了c_obj#,tab$等等雞，這些雞又繼續生蛋，則完成了數據庫字典表結構的建立
也就是說，oracle用關係型表來實現了自身結構的建立
-----------
轉自: http://www.itpub.net/199099.html
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 131142648 bytes
Fixed Size 451576 bytes
Variable Size 104857600 bytes
Database Buffers 25165824 bytes
Redo Buffers 667648 bytes
Database mounted.
SQL> alter session set sql_trace = true;
Session altered.
SQL> alter database open;
Database altered.
SQL>
首先我們來參考跟蹤文件的前部分(參考附件)
這是第一個對象的創建
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))
接下來我們來看執行的是
select line#, sql_text
from
bootstrap$ where obj# != :1
(這裏實際上是逐步提取內容建立字典表本身的結構,根據後面內容可知)
那麼在這裏我們在數據庫中來看看 bootstap$
SQL> desc bootstrap$
Name Null? Type
----------------------------------------- -------- ----------------------------
LINE# NOT NULL NUMBER
OBJ# NOT NULL NUMBER
SQL_TEXT NOT NULL VARCHAR2(4000)
SQL>
SQL> select count(*) from bootstrap$;
57
SQL>
SQL> select obj#,sql_text from bootstrap$ where rownum<11;
-1
8.0.0.0.0
0
CREATE ROLLBACK SEGMENT SYSTEM STORAGE ( INITIAL 112K NEXT 1024K MINEXTENTS 1 M
AXEXTENTS 32765 OBJNO 0 EXTENTS (FILE 1 BLOCK 9))
8
CREATE CLUSTER C_FILE#_BLOCK#("TS#" NUMBER,"SEGFILE#" NUMBER,"SEGBLOCK#" NUMBER)
PCTFREE 10 PCTUSED 40 INITRANS 2 MAXTRANS 255 STORAGE ( INITIAL 24K NEXT 1024K
MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJNO 8 EXTENTS (FILE 1 BLOCK
73)) SIZE 225
9
CREATE INDEX I_FILE#_BLOCK# ON CLUSTER C_FILE#_BLOCK# PCTFREE 10 INITRANS 2 MAXT
RANS 255 STORAGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PC
TINCREASE 0 OBJNO 9 EXTENTS (FILE 1 BLOCK 81))
14
CREATE TABLE SEG$("FILE#" NUMBER NOT NULL,"BLOCK#" NUMBER NOT NULL,"TYPE#" NUMBE
R NOT NULL,"TS#" NUMBER NOT NULL,"BLOCKS" NUMBER NOT NULL,"EXTENTS" NUMBER NOT N
ULL,"INIEXTS" NUMBER NOT NULL,"MINEXTS" NUMBER NOT NULL,"MAXEXTS" NUMBER NOT NUL
L,"EXTSIZE" NUMBER NOT NULL,"EXTPCT" NUMBER NOT NULL,"USER#" NUMBER NOT NULL,"LI
STS" NUMBER,"GROUPS" NUMBER,"BITMAPRANGES" NUMBER NOT NULL,"CACHEHINT" NUMBER NO
T NULL,"SCANHINT" NUMBER NOT NULL,"HWMINCR" NUMBER NOT NULL,"SPARE1" NUMBER,"SPA
RE2" NUMBER) STORAGE ( OBJNO 14 TABNO 2) CLUSTER C_FILE#_BLOCK#(TS#,FILE#,BLOCK
#)
5
CREATE TABLE CLU$("OBJ#" NUMBER NOT NULL,"DATAOBJ#" NUMBER,"TS#" NUMBER NOT NULL
,"FILE#" NUMBER NOT NULL,"BLOCK#" NUMBER NOT NULL,"COLS" NUMBER NOT NULL,"PCTFRE
E$" NUMBER NOT NULL,"PCTUSED$" NUMBER NOT NULL,"INITRANS" NUMBER NOT NULL,"MAXTR
ANS" NUMBER NOT NULL,"SIZE$" NUMBER,"HASHFUNC" VARCHAR2(30),"HASHKEYS" NUMBER,"F
UNC" NUMBER,"EXTIND" NUMBER,"FLAGS" NUMBER,"DEGREE" NUMBER,"INSTANCES" NUMBER,"A
VGCHN" NUMBER,"SPARE1" NUMBER,"SPARE2" NUMBER,"SPARE3" NUMBER,"SPARE4" NUMBER,"S
PARE5" VARCHAR2(1000),"SPARE6" VARCHAR2(1000),"SPARE7" DATE) STORAGE ( OBJNO 5
TABNO 2) CLUSTER C_OBJ#(OBJ#)
6
CREATE CLUSTER C_TS#("TS#" NUMBER) PCTFREE 10 PCTUSED 40 INITRANS 2 MAXTRANS 255
STORAGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREAS
E 0 OBJNO 6 EXTENTS (FILE 1 BLOCK 57))
7
CREATE INDEX I_TS# ON CLUSTER C_TS# PCTFREE 10 INITRANS 2 MAXTRANS 255 STORAGE (
INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJNO
7 EXTENTS (FILE 1 BLOCK 65))
18
CREATE TABLE OBJ$("OBJ#" NUMBER NOT NULL,"DATAOBJ#" NUMBER,"OWNER#" NUMBER NOT N
ULL,"NAME" VARCHAR2(30) NOT NULL,"NAMESPACE" NUMBER NOT NULL,"SUBNAME" VARCHAR2(
30),"TYPE#" NUMBER NOT NULL,"CTIME" DATE NOT NULL,"MTIME" DATE NOT NULL,"STIME"
DATE NOT NULL,"STATUS" NUMBER NOT NULL,"REMOTEOWNER" VARCHAR2(30),"LINKNAME" VAR
CHAR2(128),"FLAGS" NUMBER,"OID$" RAW(16),"SPARE1" NUMBER,"SPARE2" NUMBER,"SPARE3
" NUMBER,"SPARE4" VARCHAR2(1000),"SPARE5" VARCHAR2(1000),"SPARE6" DATE) PCTFREE
10 PCTUSED 40 INITRANS 1 MAXTRANS 255 STORAGE ( INITIAL 16K NEXT 1024K MINEXTEN
TS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 OBJNO 18 EXTENTS (FILE 1 BLOCK 121))
36
CREATE UNIQUE INDEX I_OBJ1 ON OBJ$(OBJ#) PCTFREE 10 INITRANS 2 MAXTRANS 255 STOR
AGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 O
BJNO 36 EXTENTS (FILE 1 BLOCK 217))
10 rows selected.
SQL>
由這裏我們可以看出，bootstrap$ 中實際上是記錄了一些數據庫系統基本對象的創建語句
那對於我們數據庫來說，也可以看做建立一個表結構，通過這個結構可以通過關係型數據庫的方式去獲取文件中數據
ok,接下來我們看看trace文件中的內容，發現
CREATE ROLLBACK SEGMENT SYSTEM STORAGE ( INITIAL 112K NEXT 1024K MINEXTENTS
1 MAXEXTENTS 32765 OBJNO 0 EXTENTS (FILE 1 BLOCK 9))
在數據庫系統表空間的頭部創建了系統回滾段（block 9 開始，1---8 屬於數據文件頭）
再往下
CREATE CLUSTER C_OBJ#("OBJ#" NUMBER) PCTFREE 5 PCTUSED 40 INITRANS 2 MAXTRANS
255 STORAGE ( INITIAL 136K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 OBJNO 2 EXTENTS (FILE 1 BLOCK 25)) SIZE 800
這裏同樣是直接指定了該cluster 的段頭位置 block 25
SQL> select file_id,block_id from dba_extents where segment_name = 'C_OBJ#';
1 25
1 33
1 41
1 3241
1 4441
1 4473
1 4489
1 4513
1 4529
1 4561
1 4585
1 4609
1 4641
1 4681
1 4753
1 4833
1 4873
1 12681
1 23689
1 26249
20 rows selected.
CREATE INDEX I_OBJ# ON CLUSTER C_OBJ# PCTFREE 10 INITRANS 2 MAXTRANS 255
STORAGE ( INITIAL 64K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 OBJNO 3 EXTENTS (FILE 1 BLOCK 49))
CREATE TABLE TAB$("OBJ#" NUMBER NOT NULL,"DATAOBJ#" NUMBER,"TS#" NUMBER NOT
NULL,"FILE#" NUMBER NOT NULL,"BLOCK#" NUMBER NOT NULL,"BOBJ#" NUMBER,"TAB#"
NUMBER,"COLS" NUMBER NOT NULL,"CLUCOLS" NUMBER,"PCTFREE$" NUMBER NOT NULL,
"PCTUSED$" NUMBER NOT NULL,"INITRANS" NUMBER NOT NULL,"MAXTRANS" NUMBER NOT
NULL,"FLAGS" NUMBER NOT NULL,"AUDIT$" VARCHAR2(38) NOT NULL,"ROWCNT" NUMBER,
"BLKCNT" NUMBER,"EMPCNT" NUMBER,"AVGSPC" NUMBER,"CHNCNT" NUMBER,"AVGRLN"
NUMBER,"AVGSPC_FLB" NUMBER,"FLBCNT" NUMBER,"ANALYZETIME" DATE,"SAMPLESIZE"
NUMBER,"DEGREE" NUMBER,"INSTANCES" NUMBER,"INTCOLS" NUMBER NOT NULL,
"KERNELCOLS" NUMBER NOT NULL,"PROPERTY" NUMBER NOT NULL,"TRIGFLAG" NUMBER,
"SPARE1" NUMBER,"SPARE2" NUMBER,"SPARE3" NUMBER,"SPARE4" VARCHAR2(1000),
"SPARE5" VARCHAR2(1000),"SPARE6" DATE) STORAGE ( OBJNO 4 TABNO 1) CLUSTER
C_OBJ#(OBJ#)
我們可以看到，從tab$ 開始，存儲發生了變化，
STORAGE ( OBJNO 4 TABNO 1) CLUSTER C_OBJ#(OBJ#)
那這裏的 objno 4 tabno 1 表示什麼意思呢?(通過 cluster C_OBJ#(OBJ#)我們就可以找到表tab$自身)
SQL> select * from tab$ where obj# = 4 and tab# = 1;
OBJ# DATAOBJ# TS# FILE# BLOCK# BOBJ# TAB#
---------- ---------- ---------- ---------- ---------- ---------- ----------
COLS CLUCOLS PCTFREE$ PCTUSED$ INITRANS MAXTRANS FLAGS
---------- ---------- ---------- ---------- ---------- ---------- ----------
AUDIT$ ROWCNT BLKCNT EMPCNT
-------------------------------------- ---------- ---------- ----------
AVGSPC CHNCNT AVGRLN AVGSPC_FLB FLBCNT ANALYZETI SAMPLESIZE
---------- ---------- ---------- ---------- ---------- --------- ----------
DEGREE INSTANCES INTCOLS KERNELCOLS PROPERTY TRIGFLAG SPARE1
---------- ---------- ---------- ---------- ---------- ---------- ----------
SPARE2 SPARE3
---------- ----------
SPARE4
--------------------------------------------------------------------------------
SPARE5
--------------------------------------------------------------------------------
SPARE6
---------
4 2 0 1 25 2 1
37 1 0 0 0 0 17
-------------------------------- 921 428 83
2381 0 139 6368 7 11-AUG-03 921
37 37 1024 0 0
06-AUG-03
SQL>
由這裏可以看出，存儲參數從這裏開始，就從數據文件中固定表的記錄中取出來
由此再往trace文件看下去，就會發現這個時候數據庫已經可以通過已有信息從系統表空間文件中提取結構信息和數據信息
我們看上面關於存儲的定義
CREATE CLUSTER C_OBJ#("OBJ#" NUMBER) PCTFREE 5 PCTUSED 40 INITRANS 2 MAXTRANS
255 STORAGE ( INITIAL 136K NEXT 1024K MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 OBJNO 2 EXTENTS (FILE 1 BLOCK 25)) SIZE 800
這裏的extents 指明瞭是 block 25,我們假設在初始化參數文件中db_block_size設置不當，則必然導致文件位置定位錯誤
之所以要來研究這個問題（以前研究了今天寫出來而已），是因爲最早思考這樣一個問題
我們要查詢自己系統的一個表，則首先是去數據字典中找到該表的結構性信息
這些結構性信息存儲在數據字典表中，但我們又從哪裏獲得數據字典表本身的結構性信息呢？
雖然從表中我們可以查詢到字典表本身的結構性信息，那在數據庫open的時候最初是如何確定結構的？
是寫死在程序中呢？還是怎樣處理的
由上面內容我們可以看出，程序中只要提供 bootstrap$ 的創建腳本，確定好bootstap$的結構同時指定了段頭的位置
然後就能通過段頭去獲取bootstrap$中的內容，而這些內容就是爲一些字典表創建結構的sql_text
這樣就因了bootstrap$這個天生的蛋，孵化出了c_obj#,tab$等等雞，這些雞又繼續生蛋，則完成了數據庫字典表結構的建立
也就是說，oracle用關係型表來實現了自身結構的建立
-----------
轉自: http://www.itpub.net/199099.html