在Oracle10g中,Oracle对v$database视图做出增强,增加了很多字段,其中一个重要字段是:CURRENT_SCN,代表数据库当前的SCN:

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for Linux: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production

SQL> desc v$database
Name Null? Type
----------------------------------------- -------- ----------------------------
DBID NUMBER
NAME VARCHAR2(9)
...................
CURRENT_SCN NUMBER
FLASHBACK_ON VARCHAR2(18)
SUPPLEMENTAL_LOG_DATA_FK VARCHAR2(3)
SUPPLEMENTAL_LOG_DATA_ALL VARCHAR2(3)
DB_UNIQUE_NAME VARCHAR2(30)
STANDBY_BECAME_PRIMARY_SCN NUMBER
FS_FAILOVER_STATUS VARCHAR2(21)
FS_FAILOVER_CURRENT_TARGET VARCHAR2(30)
FS_FAILOVER_THRESHOLD NUMBER
FS_FAILOVER_OBSERVER_PRESENT VARCHAR2(7)
FS_FAILOVER_OBSERVER_HOST VARCHAR2(512) 

这个字段来自底层基础表x$kccdi ,其中的字段为:DICUR_SCN , DI代表Database Information ,cur_scn 代表 current SCN:

SQL> desc x$kccdi
Name Null? Type
----------------------------------------- -------- -----------------
ADDR RAW(4)
INDX NUMBER
...............
DIPLID NUMBER
DIPLN VARCHAR2(101)
DICUR_SCN VARCHAR2(16)
DIDBUN VARCHAR2(30)
DIFSTS NUMBER
DIFOPR NUMBER
DIFTHS NUMBER
DIFTGT VARCHAR2(30)
DIFOBS VARCHAR2(512)

这个SCN值和9i中引入的dbms_flashback.get_system_change_number获得的值相同:

SQL> select
2 (select dicur_scn from x$kccdi ) a,
3 (select dbms_flashback.get_system_change_number a from dual) b
4 from dual;