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Oracle10g v$database视图SCN增强

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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。

作者：盖国强来源：eygle.com 2007年9月17日

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;

A B
---------------- ------------------
8905603606859 8905603606859

v$database在Oracle10g中构建的语句如下,引用供参考:

SELECT di.inst_id, di.didbi, di.didbn,
TO_DATE (di.dicts, 'MM/DD/RR HH24:MI:SS', 'NLS_CALENDAR=Gregorian'),
TO_NUMBER (di.dirls),
TO_DATE (di.dirlc, 'MM/DD/RR HH24:MI:SS', 'NLS_CALENDAR=Gregorian'),
TO_NUMBER (di.diprs),
TO_DATE (di.diprc, 'MM/DD/RR HH24:MI:SS', 'NLS_CALENDAR=Gregorian'),
DECODE (di.dimla, 0, 'NOARCHIVELOG', 1, 'ARCHIVELOG', 'MANUAL'),
TO_NUMBER (di.discn), TO_NUMBER (di.difas),
DECODE (BITAND (di.diflg, 256),
256, 'CREATED',
DECODE (BITAND (di.diflg, 1024),
1024, 'STANDBY',
DECODE (BITAND (di.diflg, 32768),
32768, 'CLONE',
DECODE (BITAND (di.diflg, 4096),
4096, 'BACKUP',
'CURRENT'
)
)
)
),
TO_DATE (di.dicct, 'MM/DD/RR HH24:MI:SS', 'NLS_CALENDAR=Gregorian'),
di.dicsq, TO_NUMBER (di.dickp_scn),
TO_DATE (di.dickp_tim, 'MM/DD/RR HH24:MI:SS', 'NLS_CALENDAR=Gregorian'),
DECODE (BITAND (di.diflg, 4),
4, 'REQUIRED',
DECODE (di.diirs, 0, 'NOT ALLOWED', 'ALLOWED')
),
TO_DATE (di.divts, 'MM/DD/RR HH24:MI:SS', 'NLS_CALENDAR=Gregorian'),
DECODE (di.didor,
0, 'MOUNTED',
DECODE (di.didor, 1, 'READ WRITE', 'READ ONLY')
),
DECODE (BITAND (di.diflg, 65536),
65536, 'MAXIMUM PROTECTION',
DECODE (BITAND (di.diflg, 128),
128, 'MAXIMUM AVAILABILITY',
DECODE (BITAND (di.diflg, 134217728),
134217728, 'RESYNCHRONIZATION',
DECODE (BITAND (di.diflg, 8),
8, 'UNPROTECTED',
'MAXIMUM PERFORMANCE'
)
)
)
),
DECODE (di.diprt,
1, 'MAXIMUM PROTECTION',
2, 'MAXIMUM AVAILABILITY',
3, 'RESYNCHRONIZATION',
4, 'MAXIMUM PERFORMANCE',
5, 'UNPROTECTED',
'UNKNOWN'
),
DECODE (di.dirae,
0, 'DISABLED',
1, 'SEND',
2, 'RECEIVE',
3, 'ENABLED',
'UNKNOWN'
),
TO_NUMBER (di.diacid), TO_NUMBER (di.diacid),
DECODE (BITAND (di.diflg, 33554432),
33554432, 'LOGICAL STANDBY',
DECODE (BITAND (di.diflg, 1024),
1024, 'PHYSICAL STANDBY',
'PRIMARY'
)
),
TO_NUMBER (di.diars),
DECODE (BITAND (difl2, 1), 1, 'ENABLED', 'DISABLED'),
DECODE (di.disos,
0, 'IMPOSSIBLE',
1, 'NOT ALLOWED',
2, 'SWITCHOVER LATENT',
3, 'SWITCHOVER PENDING',
4, 'TO PRIMARY',
5, 'TO STANDBY',
6, 'RECOVERY NEEDED',
7, 'SESSIONS ACTIVE',
8, 'PREPARING SWITCHOVER',
9, 'PREPARING DICTIONARY',
10, 'TO LOGICAL STANDBY',
'UNKNOWN'
),
DECODE (di.didgd, 0, 'DISABLED', 'ENABLED'),
DECODE (BITAND (di.diflg, 1048576),
1048576, 'ALL',
DECODE (BITAND (di.diflg, 2097152),
2097152, 'STANDBY',
'NONE'
)
),
DECODE (BITAND (diflg, 1073741824),
1073741824, 'YES',
DECODE (BITAND (diflg, 131072 + 262144 + 524288),
0, DECODE (BITAND (difl2, 2), 0, 'NO', 'IMPLICIT'),
'IMPLICIT'
)
),
DECODE (BITAND (di.diflg, 131072), 131072, 'YES', 'NO'),
DECODE (BITAND (di.diflg, 262144), 262144, 'YES', 'NO'),
DECODE (BITAND (di.diflg, 268435456), 268435456, 'YES', 'NO'),
di.diplid, di.dipln, di2.di2rdi, di2.di2inc, TO_NUMBER (di.dicur_scn),
DECODE (BITAND (di2.di2flag, 1),
1, 'YES',
DECODE (di2.di2rsp_oldest, 0, 'NO', 'RESTORE POINT ONLY')
),
DECODE (BITAND (diflg, 524288), 524288, 'YES', 'NO'),
DECODE (BITAND (difl2, 2), 2, 'YES', 'NO'), di.didbun,
TO_NUMBER (di2.di2actiscn),
DECODE (di.difsts,
0, 'DISABLED',
1, 'BYSTANDER',
2, 'SYNCHRONIZED',
3, 'UNSYNCHRONIZED',
4, 'SUSPENDED',
5, 'STALLED',
6, 'LOADING DICTIONARY',
7, 'PRIMARY UNOBSERVED',
8, 'REINSTATE REQUIRED',
9, 'REINSTATEIN PROGRESS',
10, 'REINSTATE FAILED',
''
),
di.diftgt, di.difths,
DECODE (di.difopr, 1, 'YES', 2, 'NO', 3, 'UNKNOWN', ''), di.difobs
FROM x$kccdi di, x$kccdi2 di2

此前获取SCN可以通过如下方法:

http://www.eygle.com/faq/How.To.Get.Current.SCN.of.Database.htm

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