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如何获得当前数据库的SCN值

主要可以通过两种方式:

1.在Oracle9i及以上版本中

可以使用dbms_flashback.get_system_change_number来获得

SQL> select dbms_flashback.get_system_change_number from dual;
GET_SYSTEM_CHANGE_NUMBER
------------------------
                 2982184

2.在Oracle9i之前

可以通过查询x$ktuxe获得最接近当前系统scn值

 X$KTUXE-------------[K]ernel [T]ransaction [U]ndo Transa[x]tion [E]ntry (table)

SQL> select max(ktuxescnw*power(2,32)+ktuxescnb) from x$ktuxe;
MAX(KTUXESCNW*POWER(2,32)+KTUXESCNB)
------------------------------------
                             2980613 

3.通过oradebug获取

以前在l2g32003的站点上看到使用oradebug获取SCN的方法,转引在这里:

[oracle@neirong oracle]$ sqlplus "/ as sysdba"
SQL*Plus: Release 9.2.0.4.0 - Production on Wed Dec 21 21:04:24 2005
Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.4.0 - Production
SQL> col a for 999999999999
SQL> oradebug setmypid
Statement processed.
SQL> oradebug DUMPvar SGA kcsgscn_
kcslf kcsgscn_ [1200BC68, 1200BC88) = 00000003 BA84F392 00071266 00000000 00000000 00000000 00000000 1200B948
SQL> select to_number('3BA84F392','xxxxxxxxxxxx') a from dual;
            A
-------------
  16014177170
SQL> select dbms_flashback.get_system_change_number a from dual;
            A
-------------
  16014177255
SQL>

方法有多种,但是涉及的知识各有巧妙不同,深入研究一下都是很有意思的.

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