在"关于10g中的X$KCVFH"和"关于10g中的X$KCVFH（续）"这两篇文章里，我介绍了X$KCVFH中各个字段的详细含义，这里我们再进一步来分析一下X$KCVFH的来源。
在"关于10g中的X$KCVFH（续）"这篇文章里，我是通过把data file #1在X$KCVFH中的记录的内容和data file #1的文件头dump出来的内容做了一个对比从而完善了X$KCVFH中各个字段的含义，这里我们再次定位data file #1。
$ bbed parfile=par.txt
Password:
BBED: Release
Copyright (c) 1982, 2007, Oracle. All rights reserved.
************* !!! For Oracle Internal Use only !!! ***************
BBED> set file 1
FILE# 1
BBED> p kcvfh
struct kcvfh, 676 bytes @0
struct kcvfhbfh, 20 bytes @0
ub1 type_kcbh @0 0x0b
ub1 frmt_kcbh @1 0xa2
ub1 spare1_kcbh @2 0x00
ub1 spare2_kcbh @3 0x00
ub4 rdba_kcbh @4 0x00400001
ub4 bas_kcbh @8 0x00000000
ub2 wrp_kcbh @12 0x0000
ub1 seq_kcbh @14 0x01
ub1 flg_kcbh @15 0x04 (KCBHFCKV)
ub2 chkval_kcbh @16 0x
ub2 spare3_kcbh @18 0x0000
struct kcvfhhdr, 76 bytes @20
ub4 kccfhswv @20 0x00000000
ub4 kccfhcvn @24 0x
ub4 kccfhdbi @28 0x5091aeb3
text kccfhdbn[0] @32 I
text kccfhdbn[1] @33 P
text kccfhdbn[2] @34 R
text kccfhdbn[3] @
text kccfhdbn[4] @36 T
text kccfhdbn[5] @37 E
text kccfhdbn[6] @38 S
text kccfhdbn[7] @39 T
ub4 kccfhcsq @40 0x000017b5
ub4 kccfhfsz @44 0x
s_blkz kccfhbsz @48 0x00
ub2 kccfhfno @52 0x0001
ub2 kccfhtyp @54 0x0003
ub4 kccfhacid @56 0x00000000
ub4 kccfhcks @60 0x00000000
text kccfhtag[0] @64
......省略显示部分内容
text kccfhtag[31] @95
ub4 kcvfhrdb @96 0x00400179
struct kcvfhcrs, 8 bytes @100
ub4 kscnbas @100 0x00000008
ub2 kscnwrp @104 0x0000
ub4 kcvfhcrt @108 0x
ub4 kcvfhrlc @112 0x28144e35
struct kcvfhrls, 8 bytes @116
ub4 kscnbas @116 0x00086983
ub2 kscnwrp @120 0x0000
ub4 kcvfhbti @124 0x00000000
struct kcvfhbsc, 8 bytes @128
ub4 kscnbas @128 0x00000000
ub2 kscnwrp @132 0x0000
ub2 kcvfhbth @136 0x0000
ub2 kcvfhsta @138 0x2004 (KCVFHOFZ)
struct kcvfhckp, 160 bytes @484
struct kcvcpscn, 8 bytes @484
ub4 kscnbas @484 0x1697d667
ub2 kscnwrp @488 0x0009
ub4 kcvcptim @492 0x2904b211
ub2 kcvcpthr @496 0x0001
union u, 12 bytes @500
struct kcvcprba, 12 bytes @500
ub4 kcrbaseq @500 0x00000049
ub4 kcrbabno @504 0x00065762
ub2 kcrbabof @508 0x0010
ub1 kcvcpetb[0] @512 0x02
......省略显示部分内容
ub1 kcvcpetb[128] @640 0x00
ub4 kcvfhcpc @140 0x
ub4 kcvfhrts @144 0x28144e27
ub4 kcvfhccc @148 0x
struct kcvfhbcp, 160 bytes @152
struct kcvcpscn, 8 bytes @152
ub4 kscnbas @152 0x00000000
ub2 kscnwrp @156 0x0000
ub4 kcvcptim @160 0x00000000
ub2 kcvcpthr @164 0x0000
union u, 12 bytes @168
struct kcvcprba, 12 bytes @168
ub4 kcrbaseq @168 0x00000000
ub4 kcrbabno @172 0x00000000
ub2 kcrbabof @176 0x0000
ub1 kcvcpetb[0] @180 0x00
......省略显示部分内容
ub1 kcvcpetb[128] @308 0x00
ub4 kcvfhbhz @312 0x00000000
struct kcvfhxcd, 16 bytes @316
ub4 space_kcvmxcd[0] @316 0x00000000
ub4 space_kcvmxcd[1] @320 0x00000000
ub4 space_kcvmxcd[2] @324 0x00000000
ub4 space_kcvmxcd[3] @328 0x00000000
word kcvfhtsn @332 0
ub2 kcvfhtln @336 0x0006
text kcvfhtnm[0] @338 S
text kcvfhtnm[1] @339 Y
text kcvfhtnm[2] @340 S
text kcvfhtnm[3] @341 T
text kcvfhtnm[4] @342 E
text kcvfhtnm[5] @
......省略显示部分内容
text kcvfhtnm[29] @367
ub4 kcvfhrfn @368 0x00000001
struct kcvfhrfs, 8 bytes @372
ub4 kscnbas @372 0x00000000
ub2 kscnwrp @376 0x0000
ub4 kcvfhrft @380 0x00000000
struct kcvfhafs, 8 bytes @384
ub4 kscnbas @384 0x00000000
ub2 kscnwrp @388 0x0000
ub4 kcvfhbbc @392 0x00000000
ub4 kcvfhncb @396 0x00000000
ub4 kcvfhmcb @400 0x00000000
ub4 kcvfhlcb @404 0x00000000
ub4 kcvfhbcs @408 0x00000000
ub2 kcvfhofb @412 0x
ub2 kcvfhnfb @414 0x
ub4 kcvfhprc @416 0x
struct kcvfhprs, 8 bytes @420
ub4 kscnbas @420 0x00000001
ub2 kscnwrp @424 0x0000
struct kcvfhprfs, 8 bytes @428
ub4 kscnbas @428 0x00000000
ub2 kscnwrp @432 0x0000
ub4 kcvfhtrt @444 0x00000000
这里我们可以从结果里看到X$KCVFH实际上是来源于kcvfh这个struct。
有人曾在itpub上问x$kcvfh中的FHRDB是什么意思？其实FHRDB在10g里就是代表root dba的意思，Root dba: This field only occurs in data file #1, and is the location of blocks required during bootstrapping the data dictionary (bootstrap$)。
从上面的结果里我们可以看到现在的root dba是0x00400179：
SQL> exec sys.cdba('00400179','H');
.
The file is 1
The block is 377
PL/SQL procedure successfully completed
$ bbed parfile=par.txt
Password:
BBED: Release
Copyright (c) 1982, 2007, Oracle. All rights reserved.
************* !!! For Oracle Internal Use only !!! ***************
BBED> set file 1
FILE# 1
BBED> set block 377
BLOCK# 377
BBED> p ktemh
struct ktemh, 16 bytes @92
ub4 count_ktemh @92 0x00000001
ub4 next_ktemh @96 0x00000000
ub4 obj_ktemh @100 0x00000038
ub4 flag_ktemh @104 0x40000000
可以看到这里root dba指向的object实际是0x00000038。
SQL> select to_number('38','XX') from dual;
TO_NUMBER('38','XX')
--------------------
56
SQL> select name from sys.obj$ where obj#=56;
NAME
------------------------------
BOOTSTRAP$
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