很多時候，數據庫有故障打不開，需要用到推進scn的技術，這里介紹下12c及以上版本的oracle怎么推進數據庫的scn。
經測試發現，數據庫mount和open狀態下都可以通過此方法推進SCN。
Session1：
查詢當前SCN
SQL> select current_scn from v$database;???????????????
CURRENT_SCN
-----------
?2910718245
查詢當前SCN轉成16進制后的值
SQL> select to_char(2910718245,'xxxxxxxxxxxx') from dual;
TO_CHAR(29107
-------------
???? ad7e0925
查詢預修改的SCN轉換成16進制后的值
SQL> select to_char(3910718245,'xxxxxxxxxxxx') from dual;
TO_CHAR(39107
-------------
???? e918d325
SQL>
SQL> oradebug setmypid
Statement processed.
SQL> oradebug dumpvar sga kcsgscn_
kscn8 kcsgscn_ [060017E98, 060017EA0) = AD7E093B 00000000
060017E98是SCN BASE值，我們待會修改的就是他，修改成多少，數據庫SCN就是多少
AD7E093B是當前的SCN值，可以理解為060017E98是一個代號x，當前的x等于AD7E093B
Session2:
[oracle@redhat19c11 ~]$ ps -ef|grep LOCAL=YES
oracle??? 9824? 9730? 0 Feb22 ???????? 00:00:01 oracleorcl (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle?? 18621? 8636? 0 01:18 pts/1??? 00:00:00 grep --color=auto LOCAL=YES
oracle?? 20109 20105? 0 Feb15 ???????? 00:00:13 oracletestdb19c (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
本次測試庫是orcl，因此選9824
[oracle@redhat19c11 ~]$ gdb $ORACLE_HOME/bin/oracle 9824
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-114.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <The GNU General Public License v3.0- GNU Project - Free Software Foundation>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.? Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
。。。。。。(中間省略)
(gdb) set *((int *) 0x060017E98) = 0xe918d325??????? --->將SCN BASE修改為剛才查出來的值
(gdb) quit
A debugging session is active.
??????? Inferior 1 [process 9824] will be detached.
Quit anyway? (y or n) y
Detaching from program: /oracle/app/product/19.3.0/db_1/bin/oracle, process 9824
返回session1查詢，修改成功：
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
?3910718287
重啟數據庫，也正常：
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup;
ORACLE instance started.
Total System Global Area 2466250400 bytes
Fixed Size????????????????? 9137824 bytes
Variable Size???????????? 603979776 bytes
Database Buffers???????? 1845493760 bytes
Redo Buffers??????????????? 7639040 bytes
Database mounted.
Database opened.
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
?3910719415
