Oracle 10g 中 X$KCVFH 说明
一. X$表说明
之前整理了一篇有关动态性能视图的blog：
http://blog.csdn.net/tianlesoftware/article/details/5863191
http://blog.csdn.net/tianlesoftware/article/details/5583655
The fixed X$tables are no real tables; you will not find them in any database schema. Thesevirtual tables provide a SQL interface to Oracle memory structures; that is,you can retrieve (real-time) information from memory structures using SQLqueries.
X$表包含了特定实例的各方面的信息，X$表在oracle的不同版本里很可能是不一样的，是Oracle数据库的运行基础，如当前的配置信息，连接到实例的会话，以及丰富而有价值的性能信息。X$表并不是驻留在数据库文件的永久表或临时表。
X$表仅仅驻留在内存中，当实例启动时，由Oracle应用程序动态创建，在内存中进行实时的维护。它们中的大多数至少需要装载或已经打开的数据库。X$表为SYS用户所拥有，并且是只读的。不能进行DML(更新，插入，删除)。X$表对数据库来说至关重要，所以Oracle不允许SYSDBA之外的用户直接访问，显示授权不被允许。
可以从v$fixed_table中查到X$：
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise EditionRelease 10.2.0.5.0 - Prod
PL/SQL Release 10.2.0.5.0 - Production
CORE10.2.0.5.0 Production
TNS for Linux: Version 10.2.0.5.0 -Production
NLSRTL Version 10.2.0.5.0 - Production
SQL> select count(*) from v$fixed_tablewhere name like 'X$%';
COUNT(*)
----------
620
以上是Oracle10.2.0.5 版本里的x$表的数量，在Oracle 11g里又有大幅增加：
SQL>select count(*) fromv$fixed_table where name like 'X$%';
COUNT(*)
----------
945
关于X$表，其创建信息我们也可以通过bootstrap$表查看，该表中记录了数据库启动的基本及驱动信息。bootstrap$实际上存储的是数据字典的基表的定义，如OBJ$,C_OBJ$,TAB$等等。Oracle通过读取这些定义创建数据字典的基表，进而创建数据字典。有关bootstrap$会另篇说明。
SQL>select * from bootstrap$;
二.Oracle10g X$KCVFH说明
X$KCVFH是GV$DATAFILE_HEADER的内部视图，不同版本的Oracle，X$KCVFH 的结构可能不同，如下说明基于Oracle 10gR2版本。这部分工作是dbsnake 做的，直接摘取自dbsnake的blog。
2.1 字典结构及含义
SQL> desc x$kcvfh
相关字段的描述：
Column Name Data Type Description
ADDR RAW(4) ADDRESS
INDX NUMBER INDEX
INST_ID NUMBER INSTANCE ID
HXFIL NUMBER FILE#，Datafile number (from control file)
HXONS NUMBER ONLINE | OFFLINE (from control file),HXONS为 0表示'OFFLINE',为其他值表示 'ONLINE'
HXSTS VARCHAR2(16)
HXERR NUMBER ERROR，decode(HXERR, 0, NULL,
1,'FILE MISSING',
2,'OFFLINE NORMAL',
3,'NOT VERIFIED',
4,'FILE NOT FOUND',
5,'CANNOT OPEN FILE',
6,'CANNOT READ HEADER',
7,'CORRUPT HEADER',
8,'WRONG FILE TYPE',
9,'WRONG DATABASE',
10,'WRONG FILE NUMBER',
11,'WRONG FILE CREATE',
12,'WRONG FILE CREATE',
16,'DELAYED OPEN',
14,'WRONG RESETLOGS',
15,'OLD CONTROLFILE',
'UNKNOWN ERROR')
HXVER NUMBER FORMAT，Indicates the format for the header block. The possible values are 6, 7, 8, or 0.
6 - indicates Oracle Version 6；
7 - indicates Oracle Version 7；
8 - indicates Oracle Version 8；
0 - indicates the format could not be determined (for example, the header could not be read)
FHSWV NUMBER
FHCVN NUMBER Compatibility Vsn
FHDBI NUMBER DBID
FHDBN VARCHAR2(9) DB NAME
FHCSQ NUMBER controlfile sequence number
FHFSZ NUMBER BLOCKS, Current datafile size in blocks
FHBSZ NUMBER datafile block size
FHFNO NUMBER Tablespace datafile number
FHTYP NUMBER Type:
1 control file
2 redo log file
3 vanilla db file; that is, normal data, index, and undo blocks
4 backup control file
5 backup piece
6 temporary db file
FHRDB NUMBER Root dba: This field only occurs in data file #1, and is the location of blocks required during bootstrapping the data dictionary (bootstrap$)
FHCRS VARCHAR2(16) CREATION_CHANGE#，Datafile creation change#
FHCRT VARCHAR2(20) CREATION_TIME，Datafile creation timestamp
FHRLC VARCHAR2(20) RESETLOGS_TIME, Resetlogs timestamp
FHRLC_I NUMBER reset logs count
FHRLS VARCHAR2(16) RESETLOGS_CHANGE#, Resetlogs change#
FHPRC VARCHAR2(20) prev reset logs timestamp
FHPRC_I NUMBER prev reset logs count
FHPRS VARCHAR2(16) prev reset logs SCN
FHBTI VARCHAR2(20) Time the backup started, Updated when executing BEGIN BACKUP on the tablespace. RMAN does not update this field.
FHBSC VARCHAR2(16) System change number when backup started, Updated when executing BEGIN BACKUP on the tablespace. RMAN does not update this field.
FHBTH NUMBER Thread when when backup started, Updated when executing BEGIN BACKUP on the tablespace. RMAN does not update this field.
FHSTA NUMBER The value for the column X$KCVFH.FHSTA (file header status) for an open database with an online datafiles in versions prior to version 10 were all 4, indicating an online fuzzy status. With version 10 of Oracle the first system tablespace datafile will have a different status of 8196 if the datafile is online and the database is open and not in backup mode. In Oracle 10g, the X$KCVFH.FHSTA column will show 8196 for system data file if COMPATIBLE is set to 10.0.0.0 or higher. The value of 8196 is a value of 0x04, as in previous releases, plus an AND'd value of 0x2000 (8192) for internal uses. If COMPATIBLE is set to 9.2.0 (lowest possible value for Oracle 10g), the FHSTA column for system datafile will have a value of 4.
In Oracle10g, the COMPATIBLE value is irreversible if advanced to a higher value. So the value of 8196 for the fhsta (status) column for the first system tablespace datafile is normal.
FHSCN VARCHAR2(16) CHECKPOINT_CHANGE#, Datafile checkpoint change#,Updated on every checkpoint, but not when in Hot backup state (not online backups). This must remain untouched when you are in hot backup mode, because you might get checkpoints between the BEGIN BACKUP and when you actually start the copying process.
FHTIM VARCHAR2(20) CHECKPOINT_TIME, Datafile checkpoint timestamp
FHTHR NUMBER THREAD#
FHRBA_SEQ NUMBER SEQUENCE，即Redo log sequence number
FHRBA_BNO NUMBER Block number，即the redo log file block number
FHRBA_BOF NUMBER Byte offset，the byte offset into the block at which the redo record starts
FHETB RAW(132) enable threads byte(这个不确定)
FHCPC NUMBER CHECKPOINT_COUNT, Datafile checkpoint count
FHRTS VARCHAR2(20) Recoverd timestamp
FHCCC NUMBER Controlfile Checkpoint Count: Saved copy of the control file record of the checkpoint count. Helps detect old control files.
FHBCP_SCN VARCHAR2(16) Backup Checkpoint SCN: Updated with the checkpoint done while file in Hot backup
FHBCP_TIM VARCHAR2(20) Backup Checkpoint TIME: Updated with the checkpoint done while file in Hot backup
FHBCP_THR NUMBER Backup Checkpoint Thread: Updated with the checkpoint done while file in Hot backup
FHBCP_RBA_ SEQ NUMBER Backup Checkpoint Sequence, 即Redo log sequence number: Updated with the checkpoint done while file in Hot backup
FHBCP_RBA_ BNO NUMBER the redo log file block number, Updated with the checkpoint done while file in Hot backup
FHBCP_RBA_ BOF NUMBER Byte offset，the byte offset into the block at which the redo record starts, Updated with the checkpoint done while file in Hot backup
FHBCP_ETB RAW(132) enable threads byte(不确定)
FHBHZ NUMBER begin hot backup file size
FHXCD RAW(16) External cache id: Used to ensure that concurrent instances access data through consistent external cache
FHTSN NUMBER TS#，Tablespace number
FHTNM VARCHAR2(30) TABLESPACE_NAME, Tablespace name
FHRFN NUMBER RFILE#, Tablespace relative datafile number
FHAFS VARCHAR2(16) absolute fuzzy scn, 即Minimum PITR SCN
FHRFS VARCHAR2(16) The SCN at which the recovery of this file will be complete (no longer fuzzy). Both above fuzzy SCNs must be zero unless a fuzzy flag is set, and must be greater than the checkpoint SCN
FHRFT VARCHAR2(20) The time at which the recovery of this file will be complete (no longer fuzzy).
HXIFZ NUMBER File is fuzzy (YES | NO)，decode(hxifz, 0,'NO', 1,'YES', NULL)
HXNRCV NUMBER File needs media recovery (YES | NO)，decode(hxnrcv, 0,'NO', 1,'YES', NULL)
HXFNM VARCHAR2(513) NAME, Datafile name
FHPOFB NUMBER
FHPNFB NUMBER
FHPRE10 NUMBER
FHFIRSTUNRECSCN VARCHAR2(16) UNRECOVERABLE_CHANGE#, Last unrecoverable change number made to this datafile. If the database is in ARCHIVELOG mode, then this column is updated when an unrecoverable operation completes. If the database is not in ARCHIVELOG mode, this column does not get updated.
FHFIRSTUNRECTIME VARCHAR2(20) UNRECOVERABLE_TIME, Timestamp of the last unrecoverable change. This column is updated only if the database is in ARCHIVELOG mode.
HXLMDBA NUMBER SPACE_HEADER, The amount of space currently being used and the amount that is free, as identified in the space header. decode(hxlmdba, 0, NULL, hxlmdba)
HXLMLD_SCN VARCHAR2(16) LAST_DEALLOC_SCN, Last deallocated SCN
2.2 X$KCVFH的常见用法
2.2.1 判断datafile是否需要recover，如果需要recover，那么需要至少需要recover到什么SCN，即执行如下查询：
SQL> select max(fhafs) from x$kcvfh;
MAX(FHAFS)
----------------
0
如果返回返回结果大于0，则表示数据库处于不一致的状态，需要recover到上述查询结果中的SCN。
2.2.2 判断datafile做recover需要的archive log的sequence是多少，也就是说做recover到这个sequence，那么control file和datafile header中的记录就一致了。
即执行如下查询：
SQL> select HXFILFile_num,substr(HXFNM,1,45) File_name, FHSCN SCN,FHRBA_SEQ Sequence fromX$KCVFH;
FILE_NUM FILE_NAME SCN SEQUENCE
---------- ------------------------------------------------------- ----------
1 /u01/app/oracle/oradata/anqing/system01.dbf 1329249 69
2 /u01/app/oracle/oradata/anqing/undotbs01.dbf 1329249 69
3 /u01/app/oracle/oradata/anqing/sysaux01.dbf 1329249 69
4 /u01/app/oracle/oradata/anqing/users01.dbf 1329249 69
5 /u01/app/oracle/oradata/anqing/example01.dbf 1329249 69
三. X$KCVFH 的出处
在第二节列出了x$kcvfh 大部分字段的含义。 这个含义也是dbsnake 自己推出来的。 具体的方法就是将file #1 的datafile header（第一个block） dump 出来，然后用其值与DATA FILE #1在x$kcvfh中的内容值进行比较，这个一步是dbsnake 用自己的一个过程来实现的，我不知道其具体内容，但是通过BBED 可以看出对应的值。 也可以进行一个比较。
至于为什么x$kcvfh的内容放在file #1里，这个是Oracle 的规定。
3.1 使用BBED查看kcvfh 内容
http://blog.csdn.net/tianlesoftware/article/details/5006580
http://blog.csdn.net/tianlesoftware/article/details/6684505
先查看一个File #1 对应的表空间，是system：
SQL> select file_id,file_name fromdba_data_files;
FILE_ID FILE_NAME
-------------------------------------------------------
4 /u01/app/oracle/oradata/anqing/users01.dbf
3 /u01/app/oracle/oradata/anqing/sysaux01.dbf
2 /u01/app/oracle/oradata/anqing/undotbs01.dbf
1 /u01/app/oracle/oradata/anqing/system01.dbf
5 /u01/app/oracle/oradata/anqing/example01.dbf
用BBED 工具查看一下File #1 中kcvfh 的内容和对应的值：
dave:/u01> cat filelist.txt
1/u01/app/oracle/oradata/anqing/system01.dbf
dave:/u01> cat bbed.par
blocksize=8192
listfile=/u01/filelist.txt
mode=edit
dave:/u01>bbed parfile=/u01/bbed.par
Password:
BBED: Release 2.0.0.0.0 - LimitedProduction on Sun Oct 30 15:51:16 2011
Copyright (c) 1982, 2007, Oracle. All rights reserved.
************* !!! For Oracle Internal Useonly !!! ***************
BBED> show
FILE# 1
BLOCK# 1
OFFSET 0
DBA 0x00400001(4194305 1,1)
FILENAME/u01/app/oracle/oradata/anqing/system01.dbf
BIFILE bifile.bbd
LISTFILE /u01/filelist.txt
BLOCKSIZE 8192
MODE Edit
EDIT Unrecoverable
IBASE Dec
OBASE Dec
WIDTH 80
COUNT 512
LOGFILE log.bbd
SPOOL No
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 0x9614
ub2 spare3_kcbh@18 0x0000
struct kcvfhhdr, 76 bytes@20
ub4 kccfhswv@20 0x00000000
ub4 kccfhcvn@24 0x0a200100
ub4 kccfhdbi@28 0x296d43c7
text kccfhdbn[0] @32 A
text kccfhdbn[1]@33 N
text kccfhdbn[2]@34 Q
text kccfhdbn[3]@35 I
text kccfhdbn[4]@36 N
text kccfhdbn[5]@37 G
text kccfhdbn[6]@38
text kccfhdbn[7]@39
ub4 kccfhcsq@40 0x00000402
ub4 kccfhfsz @44 0x0000fa00
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
………..
text kccfhtag[31]@95
ub4 kcvfhrdb@96 0x00400179
struct kcvfhcrs, 8 bytes@100
ub4 kscnbas@100 0x00000009
ub2 kscnwrp@104 0x0000
ub4 kcvfhcrt@108 0x2184ef93
ub4 kcvfhrlc@112 0x2d8b028b
struct kcvfhrls, 8 bytes@116
ub4 kscnbas@116 0x0006ce7b
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, 36 bytes@484
struct kcvcpscn, 8 bytes@484
ub4 kscnbas@484 0x00144861
ub2 kscnwrp@488 0x0000
ub4 kcvcptim @492 0x2da69134
ub2 kcvcpthr@496 0x0001
union u, 12 bytes@500
struct kcvcprba, 12 bytes@500
ub4 kcrbaseq@500 0x00000045
ub4 kcrbabno@504 0x00000002
ub2 kcrbabof@508 0x0010
ub1 kcvcpetb[0]@512 0x02
……
ub1 kcvcpetb[7]@519 0x00
ub4 kcvfhcpc@140 0x00000089
ub4 kcvfhrts@144 0x2da69133
ub4 kcvfhccc@148 0x00000088
struct kcvfhbcp, 36 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
……
ub1 kcvcpetb[7]@187 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[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 0x000a
ub2 kcvfhnfb@414 0x000a
ub4 kcvfhprc@416 0x2184ef74
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
BBED>
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。这里的@符号表示的是偏移量，后面对应的是其值，dbsnake 应该是写了一个方法，直接获取了这个值。如：
ub4 kccfhcvn @240x0a200100
查看该对象对应的值：
SQL> selectto_number('0a200100','xxxxxxxxx') from dual;
TO_NUMBER('0A200100','XXXXXXXXX')
---------------------------------
169869568
3.2 Dump Datafile header
http://blog.csdn.net/tianlesoftware/article/details/6525628
Datafile Header 是datafile 中的第一个block. 要dump datafile header 不能直接使用如下命令：
alter systemdump datafile 1 block 1;
该命令会显示：
Block 1 (file header) not dumped: use dumpfile header command。
查看DSI文档403 File DumpAnalysis 一节,可以找到具体的用法：
This data file headeris in all Oracle data files, that is, files belonging to a tablespace.
The header is the samefor a temp file.
（1）Dump 'FILE_HDRSLEVEL n'
N=1: The control file’sentry of the data file. This appears before the string FILE
HEADER, and is notshown on the slide. It will be covered in the control file dump.
N=2: The control file’sentry and generic header. This has been covered in the
previous slide, and isnot shown on the above slide.
N=3: The control file’sentry, generic header, and the header information in the data
file. This causes thefile to be opened and read if the database is only mounted.
（2）Data File Header
This resides in block1, somewhere after the generic file header.
Tablespace: Name of the tablespace to which the filebelongs.
rel_fn: Relative file number
Creation SCN,time: SCN at the time thefile was created. There can not be any redo
information for thisfile prior to this SCN. The timestamp is approximate. This can be
used to distinguishbetween different files created with the same name (for example,
drop and recreate atablespace).
Backup scn,time: Updated whenexecuting BEGIN BACKUP on the tablespace.
RMAN does not updatethis field.
(The next few lines inthe dump are incorrectly indented, erroneously suggesting they
belong to the backupSCN.)
reset logscountandscn: The counter with the SCN is called theReset Log Stamp,
and is a uniqueidentification. The counter is in fact a timestamp.
Recovered at: Used during recovery to help ensure thatif many processes are used
for recovery, all areusing the same file, in case of name duplication.
Status: Flags. Here are also thefuzzyflags
KCVFHHBP 001 Hot backup-in-progress on file (fuzzy file)
KCVFHHBM 002 End hot backup marker seen (Bit only validor set in Oracle7)
KCVFHOFZ 004 Online fuzzy because it was online and dbopen
KCVFHCRM 008 Crash Recovery Media marker seen (Bit onlyvalid or set in
Oracle7)
KCVFHMFZ 010 Media recovery fuzzy - file in mediarecovery
KCVFHCMF 020 Clear media recovery (Bit only valid or setin Oracle7)
KCVFHAFZ 040 Absolutely fuzzy - fuzziness from file scan
KCVFHBCP 100 Bad Checkpoint - no enabled thread bitvec
(In Oracle7 this flagmeans: File belongs to SYSTEM tablespace)
KCVFHFMH 200 Freshly munged header. Resetlogs are notfinished.
Bit is cleared at nextcheckpoint. A set bit allows an OPEN
RESETLOGS to berepeated (for example, file headers were
updated
(this bit was set) butcontrol file record not updated)
KCVFHXCH 400 Externally cached by operating system. Ifthe server is aware
of an OS cache thatdelays writes to media, then this bit gets set,
and the server willforce a media recovery when file is reopened.
KCVFHZBA 800 Zeroed blocks allowed. File may containOracle7 unused blocks,
which are all zero.Oracle8 blocks have a nonzero initial value
with SEQ and TAIL.
KCVFHPCP 1000 Proxy copy in progress
Rootdba: This fieldonly occurs in data file #1, and is the location of blocks required
duringbootstrapping the data dictionary (bootstrap$)
CheckpointCount: Number ofcheckpoints attempted to this file (some may have
been skipped, if thefile already has a checkpoint at a later time then the checkpoint
now being attempted).Helps to detect files that have been restored.
ControlfileCheckpoint Count: Saved copy of thecontrol file record of the
checkpoint count.Helps detect old control files.
begin-hot-backupfile size: Updated when BackupSCN is updated. To cope with
data files that wereresized during backup.
Checkpoint SCN: Updated on every checkpoint, but not whenin Hot backup state
(not online backups).This must remain untouched when you are in hot backup mode,
because you might getcheckpoints between the BEGIN BACKUP and when you
actually start thecopying process.
BackupCheckpoint: Updated with thecheckpoint done while file in Hot backup.
External cacheid: Used to ensure thatconcurrent instances access data through
consistent externalcache.
Absolute FuzzySCN: Shows this file is abackup copy and is fuzzy.
Recovery fuzzySCN: The SCN at which therecovery of this file will be complete
(no longer fuzzy).
Both above fuzzy SCNsmust be zero unless a fuzzy flag is set, and must be greater
than the checkpointSCN
Comment in the codethat examines the fuzzy bits:
/* Fuzzy-Wuzzy was afile.
** Fuzzy-Wuzzy needsno redo.
** Fuzzy-Wuzzywasn't fuzzy, was he? */
（3）Data File Blocks
Data file blocks arenot covered in this course, because they have been covered in
other courses in thisseries.
这里就有两种方法来dump Datafile header：
（1） 使用sql 语句：
SQL>alter system set events 'immediate tracename file_hdrs level 3;
（2） 使用oradebug命令，这里用oradebug 命令示例
SQL> oradebug setmypid
Statement processed.
SQL> oradebug dump file_hdrs 10
Statement processed.
SQL> oradebug tracefile_name
/u01/app/oracle/admin/anqing/udump/anqing_ora_4556.trc
这里会把所有的datafile 的header 都dump 出来，我们从trace里找到file#1的dump：
DATA FILE #1:
(name #7) /u01/app/oracle/oradata/anqing/system01.dbf
creation size=0 block size=8192 status=0xehead=7 tail=7 dup=1
tablespace 0, index=1 krfil=1 prev_file=0
unrecoverablescn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:140 scn: 0x0000.0014c0c110/30/2011 17:46:40
Stopscn: 0xffff.ffffffff 10/30/2011 16:29:42
Creation Checkpointed at scn: 0x0000.00000009 06/30/2005 19:10:11
thread:0 rba:(0x0.0.0)
enabledthreads: 00000000 0000000000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
……
00000000 00000000 00000000 00000000 00000000 00000000
Offline scn: 0x0000.0006ce7a prev_range: 0
Online Checkpointed at scn: 0x0000.0006ce7b 10/09/2011 13:47:55
thread:1 rba:(0x1.2.0)
enabledthreads: 01000000 0000000000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
……
00000000 00000000 00000000 00000000 00000000 00000000
HotBackup end marker scn: 0x0000.00000000
aux_file is NOT DEFINED
V10STYLE FILE HEADER:
Compatibility Vsn = 169869568=0xa200100
Db ID=695026631=0x296d43c7, Db Name='ANQING'
Activation ID=0=0x0
Control Seq=1049=0x419, File size=64000=0xfa00
File Number=1, Blksiz=8192, File Type=3 DATA
Tablespace #0 - SYSTEM rel_fn:1
Creationat scn: 0x0000.0000000906/30/2005 19:10:11
Backup taken at scn: 0x0000.0000000001/01/1988 00:00:00 thread:0
reset logs count:0x2d8b028b scn:0x0000.0006ce7b reset logs terminal rcv data:0x0 scn: 0x0000.00000000
prevreset logs count:0x2184ef74 scn: 0x0000.00000001 prev reset logs terminal rcvdata:0x0 scn: 0x0000.00000000
recovered at 10/30/2011 17:46:38
status:0x2004 root dba:0x00400179 chkpt cnt:140 ctl cnt:139
begin-hot-backup file size: 0
Checkpointed at scn: 0x0000.0014c0c1 10/30/2011 17:46:40
thread:1 rba:(0x46.2.10)
enabledthreads: 01000000 0000000000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
…..
00000000 00000000 00000000 00000000 00000000 00000000
Backup Checkpointed at scn: 0x0000.00000000
thread:0 rba:(0x0.0.0)
enabledthreads: 00000000 0000000000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 ……
00000000 00000000 00000000 00000000 00000000 00000000
External cache id: 0x0 0x0 0x0 0x0
Absolute fuzzy scn: 0x0000.00000000
Recovery fuzzy scn: 0x0000.0000000001/01/1988 00:00:00
Terminal Recovery Stamp 01/01/1988 00:00:00
Platform Information: Creation Platform ID: 10
Current Platform ID: 10 Last Platform ID:10
Dbsnake 就是用dump 出来的值和BBED 计算出来的值进行比较推测出x$kcvfh 字典中每个字段的含义。
3.3 X$KCVFH 中的FHRDB 字段说明
刚才在DSI 403里有这么一句话：
Root dba: This fieldonly occurs in data file #1, and is the location of blocks requiredduring bootstrapping the data dictionary (bootstrap$)
事实上，x$kcvfh 中的FHRDB 就是代表这个root dba,而且这个bootstrap$ 对数据库来说还非常重要。
下面我们来验证上面的这个结论：
BBED显示的FHRDB中的值：
ub4 kcvfhrdb @960x00400179
使用如下SQL,将这个DBA地址转换称对应的block，具体参考：
http://blog.csdn.net/tianlesoftware/article/details/6529346
SQL> SELECTDBMS_UTILITY.data_block_address_file (
2 TO_NUMBER (LTRIM ('0x00400179', '0x'),'xxxxxxxx'))
3 AS file_no,
4DBMS_UTILITY.data_block_address_block (
5 TO_NUMBER (LTRIM('0x00400179', '0x'), 'xxxxxxxx'))
6 AS block_no
7 FROM DUAL;
FILE_NO BLOCK_NO
---------- ----------
1377
通过这个结果，可以看出DBA0x00400179 指向的是file 1 block 377.
我们使用BBED 命令输出377 block 里面的内容：
dave:/home/oracle> bbed parfile=/u01/bbed.par
Password:
BBED: Release 2.0.0.0.0 - LimitedProduction on Sun Oct 30 18:44:26 2011
Copyright (c) 1982, 2007, Oracle. All rights reserved.
************* !!! For Oracle Internal Useonly !!! ***************
BBED>set dba 1,377
DBA 0x00400179(4194681 1,377)
BBED> show
FILE# 1
BLOCK# 377
OFFSET 0
DBA 0x00400179(4194681 1,377)
FILENAME/u01/app/oracle/oradata/anqing/system01.dbf
BIFILE bifile.bbd
LISTFILE /u01/filelist.txt
BLOCKSIZE 8192
MODE Edit
EDIT Unrecoverable
IBASE Dec
OBASE Dec
WIDTH 80
COUNT 512
LOGFILE log.bbd
SPOOL No
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
BBED> map
File:/u01/app/oracle/oradata/anqing/system01.dbf (1)
Block: 377Dba:0x00400179
------------------------------------------------------------
Unlimited Data Segment Header
struct kcbh, 20 bytes @0
struct ktech, 72 bytes @20
struct ktemh, 16 bytes @92
struct ktetb[1], 8 bytes @108
struct ktshc, 8 bytes @4148
struct ktsfs_seg[1], 20 bytes @4156
struct ktsfs_txn[16], 320 bytes @4176
ub4tailchk@8188
BBED> p ktemh
struct ktemh, 16 bytes @92
ub4count_ktemh@92 0x00000001
ub4 next_ktemh@96 0x00000000
ub4 obj_ktemh @100 0x00000038
ub4 flag_ktemh@104 0x40000000
BBED>
这里可以看到FHRDB 对应的对象是：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$
以上测试证明：10g中X$KCVFH中字段FHRDB对应的就是bootstrap$.
这篇文章根据dbsnake 的blog 重新整理测试而来，感谢dbsnake的幸苦劳动，dbsnake的原文链接如下：
关于10g中的X$KCVFH
http://dbsnake.com/2009/05/10g-x-kcvfh.html
关于10g中的X$KCVFH（续）
http://dbsnake.com/2009/05/10g-x-kcvfh-continul.html
关于10g中的X$KCVFH（续2）
http://dbsnake.com/2009/05/10g-x-kcvfh-continue-2.html
在下一篇文章中，将重点来看一下Bootstrap$.
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