有朋友遇到一个老问题，将数据库 global_name 置空后，数据库不能open。
这类问题已经是几年前的老问题了，这里用4中方法解决。
这一篇先大概介绍一下GLOBAL_NAME对象的来龙去脉。
GLOBAL_NAME和props$对象介绍
global_name为空导致的数据库不能open—–使用gdb修复(中断oracle启动的部分监测功能)
global_name为空导致的数据库不能open—–使用dd修复(使用dd拷贝块的方式)
global_name为空导致的数据库不能open—–使用DUL修复
global_name为空导致的数据库不能open—使用BBED修复（bbed恢复update的数据）
我们知道，全局数据库名是在分布式数据库系统中用于标识数据库的唯一名称，默认为DB_NAME.DB_DOMAIN。
该默认值在数据库创建的时候被标记，如果数据库创建后手工修改了DB_NAME或者DB_DOMAIN，全局数据库名称仍然保持为数据库创建时候的DB_NAME.DB_DOMAIN。
SYS@lunarp>select * from GLOBAL_NAME; GLOBAL_NAME ------------------------------------------------------------------------------------------------------------------------------------------------------ lunarbb Elapsed: 00:00:00.01 SYS@lunarp>desc GLOBAL_NAME Name Null? Type ----------------------------------------------------------------------------------- -------- -------------------------------------------------------- GLOBAL_NAME VARCHAR2(4000) SYS@lunarp>
我们查看一下GLOBAL_NAME是什么类型的对象，其定义是怎样的：
SYS@lunarp>col object_name for a50
SYS@lunarp>select owner,object_name,object_type from dba_objects where object_name=upper('global_name');
OWNER OBJECT_NAME OBJECT_TYPE
------------------------------ -------------------------------------------------- -------------------
SYS GLOBAL_NAME VIEW
PUBLIC GLOBAL_NAME SYNONYM
Elapsed: 00:00:00.00
SYS@lunarp>select dbms_metadata.get_ddl('VIEW','GLOBAL_NAME','SYS') from dual;
CREATE OR REPLACE FORCE VIEW "SYS"."GLOBAL_NAME" ("GLOBAL_NAME") AS
select value$ from sys.props$ where name = 'GLOBAL_DB_NAME'
Elapsed: 00:00:00.02
SYS@lunarp>select dbms_metadata.get_ddl('SYNONYM','GLOBAL_NAME','PUBLIC') from dual;
CREATE OR REPLACE PUBLIC SYNONYM "GLOBAL_NAME" FOR "SYS"."GLOBAL_NAME"
Elapsed: 00:00:00.10
SYS@lunarp>
可以看到，GLOBAL_NAME实际上是已于sys.props$ where name = ‘GLOBAL_DB_NAME’的一张视图和同义词。
props$中总共多少行数据，在相同版本是固定的，我这里是11.2，因此共36行：
SYS@lunarp>select count(*) from props$;
COUNT(*)
----------
36
Elapsed: 00:00:00.01
SYS@lunarp>
props$的定义如下：
SYS@lunarp>select dbms_metadata.get_ddl('TABLE','PROPS$','SYS') from dual;
CREATE TABLE "SYS"."PROPS$"
( "NAME" VARCHAR2(30) NOT NULL ENABLE,
"VALUE$" VARCHAR2(4000),
"COMMENT$" VARCHAR2(4000)
) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255
NOCOMPRESS LOGGING
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "SYSTEM"
Elapsed: 00:00:03.89
SYS@lunarp>
看一下props$对象存储了哪些内容：
SYS@lunarp>select * from props$;
NAME VALUE$ COMMENT$
------------------------------ -------------------------------------------------- --------------------------------------------------
DICT.BASE 2 dictionary base tables version #
DEFAULT_TEMP_TABLESPACE TEMP Name of default temporary tablespace
DEFAULT_PERMANENT_TABLESPACE USERS Name of default permanent tablespace
DEFAULT_EDITION ORA$BASE Name of the database default edition
Flashback Timestamp TimeZone GMT Flashback timestamp created in GMT
TDE_MASTER_KEY_ID
DBTIMEZONE -08:00 DB time zone
DST_UPGRADE_STATE NONE State of Day Light Saving Time Upgrade
DST_PRIMARY_TT_VERSION 14 Version of primary timezone data file
DST_SECONDARY_TT_VERSION 0 Version of secondary timezone data file
DEFAULT_TBS_TYPE SMALLFILE Default tablespace type
NLS_LANGUAGE AMERICAN Language
NLS_TERRITORY AMERICA Territory
NLS_CURRENCY $ Local currency
NLS_ISO_CURRENCY AMERICA ISO currency
NLS_NUMERIC_CHARACTERS ., Numeric characters
NLS_CHARACTERSET AL32UTF8 Character set
NLS_CALENDAR GREGORIAN Calendar system
NLS_DATE_FORMAT DD-MON-RR Date format
NLS_DATE_LANGUAGE AMERICAN Date language
NLS_SORT BINARY Linguistic definition
NLS_TIME_FORMAT HH.MI.SSXFF AM Time format
NLS_TIMESTAMP_FORMAT DD-MON-RR HH.MI.SSXFF AM Time stamp format
NLS_TIME_TZ_FORMAT HH.MI.SSXFF AM TZR Time with timezone format
NLS_TIMESTAMP_TZ_FORMAT DD-MON-RR HH.MI.SSXFF AM TZR Timestamp with timezone format
NLS_DUAL_CURRENCY $ Dual currency symbol
NLS_COMP BINARY NLS comparison
NLS_LENGTH_SEMANTICS BYTE NLS length semantics
NLS_NCHAR_CONV_EXCP FALSE NLS conversion exception
NLS_NCHAR_CHARACTERSET AL16UTF16 NCHAR Character set
NLS_RDBMS_VERSION 11.2.0.3.0 RDBMS version for NLS parameters
GLOBAL_DB_NAME Global database name
EXPORT_VIEWS_VERSION 8 Export views revision #
WORKLOAD_CAPTURE_MODE CAPTURE implies workload capture is in progress
WORKLOAD_REPLAY_MODE PREPARE implies external replay clients can connec
t; REPLAY implies workload replay is in progress
NO_USERID_VERIFIER_SALT 6A58202A068B678B09CF571DC967F3EC
36 rows selected.
Elapsed: 00:00:00.00
SYS@lunarp>
当数据库正常启动时，会对PROPS$表进行全表扫描来获取PROPS$中是否含有错误信息。
一般升级的时候系统会将数据库引导对象的错误信息记录到该表的BOOTSTRAP_UPGRADE_ERROR中：
SYS@lunarp>select * from props$ where name = 'GLOBAL_DB_NAME'; NAME VALUE$ COMMENT$ ------------------------------ ------------------------------ -------------------------------------------------- GLOBAL_DB_NAME lunarbb Global database name Elapsed: 00:00:00.01 SYS@lunarp>
启动时10046跟踪的trace中：
PARSING IN CURSOR #140086496404128 len=60 dep=1 uid=0 oct=3 lid=0 tim=1407167733432924 hv=3306824342 ad='8503c550' sqlid='g64r07v2jn8nq' SELECT NULL FROM PROPS$ WHERE NAME='BOOTSTRAP_UPGRADE_ERROR' END OF STMT PARSE #140086496404128:c=17997,e=76437,p=3,cr=12,cu=0,mis=1,r=0,dep=1,og=4,plh=415205717,tim=1407167733432919 EXEC #140086496404128:c=0,e=44,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,plh=415205717,tim=1407167733433101 WAIT #140086496404128: nam='db file sequential read' ela= 60288 file#=1 block#=800 blocks=1 obj#=98 tim=1407167733493464 WAIT #140086496404128: nam='db file sequential read' ela= 14273 file#=1 block#=801 blocks=1 obj#=98 tim=1407167733507890 FETCH #140086496404128:c=999,e=74855,p=2,cr=3,cu=0,mis=0,r=0,dep=1,og=4,plh=415205717,tim=1407167733507990 STAT #140086496404128 id=1 cnt=0 pid=0 pos=1 obj=98 op='TABLE ACCESS FULL PROPS$ (cr=3 pr=2 pw=0 time=74849 us)'
从这里我们看到，读取了file#=1 block#=800和file#=1 block#=801，他们分别为props$的段头和第一个数据块的位置。
他们的对象号是obj#=98，也就是props$。
从数据库中，我们也可以证实这一点：
SYS@lunarp>select owner,segment_name,HEADER_FILE,HEADER_BLOCK from dba_segments where SEGMENT_NAME='PROPS$';
OWNER SEGMENT_NAME HEADER_FILE HEADER_BLOCK
------------------------------ -------------------------------------------------- ----------- ------------
SYS PROPS$ 1 800
Elapsed: 00:00:00.01
SYS@lunarp>
SYS@lunarp>select dbms_rowid.rowid_relative_fno(rowid) file#,
2 dbms_rowid.rowid_block_number(rowid) blk#
3 from sys.props$
4 where name = 'GLOBAL_DB_NAME';
FILE# BLK#
---------- ----------
1 801
Elapsed: 00:00:00.10
SYS@lunarp>select obj#,dataobj#,owner#,name from obj$ where obj#=98;
OBJ# DATAOBJ# OWNER# NAME
---------- ---------- ---------- ------------------------------
98 98 0 PROPS$
Elapsed: 00:00:00.01
SYS@lunarp>
