1.系統當前SCN:
兩個語句都可以:
select current_scn from v$database;
CURRENT_SCN
-----------
1859456
select dbms_flashback.get_system_change_number,
SCN_TO_TIMESTAMP(dbms_flashback.get_system_change_number) from dual;
GET_SYSTEM_CHANGE_NUMBER SCN_TO_TIMESTAMP(DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER)
---------------------------------------------------------------------------
1859442 10-JAN-17 08.57.41.000000000 PM
2..數據庫全局-檢查點 SCN,在控制文件中
select dbid,checkpoint_change# from v$database;
---------- ------------------
1457614420 1854803
3.當前數據文件檢查點SCN。在控制文件中、數據文件頭中。即checkpoint scn,表示該數據文件最近一次執行檢查點操作時的SCN
select name,checkpoint_change# from v$datafile;
NAME
CHECKPOINT_CHANGE#
------------------
+DATA/orcl/datafile/system.266.929833573 1854803
+DATA/orcl/datafile/sysaux.267.929833573 1854803
+DATA/orcl/datafile/undotbs1.268.929833573 1854803
+DATA/orcl/datafile/users.269.929833573 1854803
+DATA/orcl/datafile/undotbs2.279.929833933 1854803
查詢數據文件頭SCN的命令如下
select name,checkpoint_change# from v$datafile_header;
+DATA/orcl/datafile/system.266.929833573
1854803
+DATA/orcl/datafile/sysaux.267.929833573
1854803
+DATA/orcl/datafile/undotbs1.268.929833573
1854803
+DATA/orcl/datafile/users.269.929833573
1854803
+DATA/orcl/datafile/undotbs2.279.929833933
1854803
5.數據文件結束SCN,在數據文件頭,控制文件中。
LAST_CHANGE#,如果數據庫非正常關閉值爲NULL。正常關閉是關閉時的SCN。
實例恢復就是在打開數據庫時檢查此參數確定是否需要恢復。
數據庫OPEN時LAST_CHANGE#也爲NULL,因爲不確定SCN多少時關閉。
可以看出來,
字段 last_change# 爲空。
select name,last_change# from v$datafile;
+DATA/orcl/datafile/system.266.929833573
+DATA/orcl/datafile/sysaux.267.929833573
+DATA/orcl/datafile/undotbs1.268.929833573
+DATA/orcl/datafile/users.269.929833573
+DATA/orcl/datafile/undotbs2.279.929833933
6.日誌中所含SCN範圍
select GROUP#,sequence#,STATUS,FIRST_CHANGE#,to_char(FIRST_TIME,'yyyy/mm/dd:hh24:mi:ss') firsttime,NEXT_CHANGE#,to_char(NEXT_TIME,'yyyy/mm/dd:hh24:mi:ss') nexttime from V$log;
下面的數據是在網絡上摘錄的:
GROUP# SEQUENCE# STATUS FIRST_CHANGE# FIRSTTIME NEXT_CHANGE# NEXTTIME
---------- ---------- ---------------- ------------- ------------------- ------------ -------------------
1 145 CURRENT 2910938 2013/12/15:10:06:41 2.8147E+14 ------當前REDO日誌,所以下一次切換的SCN是無窮大,切換時間爲空。
2 143 INACTIVE 2865685 2013/12/14:20:36:08 2883589 2013/12/15:02:00:55
3 144 INACTIVE 2883589 2013/12/15:02:00:55 2910938 2013/12/15:10:06:41