紧急救援！SCN调整秘籍（二）

Whoami：5年+金融、政府、医疗领域工作经验的DBA
Certificate：PGCM、OCP、YCP
Skill：Oracle、Mysql、PostgreSQL、国产数据库
Platform：CSDN、墨天轮、公众号（呆呆的私房菜）
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SCN = （SCN_Wrap * 4294967296）+ SCN_Base
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yum -y install gdb
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SQL> select current_scn,to_char(current_scn,'xxxxxxxxx') from v$database;


CURRENT_SCN TO_CHAR(CURRENT_SCN,'XXXXXXXXX
----------- ------------------------------
    1454944     163360
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SQL> oradebug setmypid;
Statement processed.
SQL> oradebug dumpvar sga kcsgscn_;
kcslf kcsgscn_ [0600113B8, 0600113E8) = 00163591 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 60049740 00000000


SCN Base：内存地址 0600113B8 开始的4字节值为 00 16 35 91（16进制），转为十进制为 1455505
SCN Wrap：后续4字节为 00000000，因SCN未超过4字节上限（2^32=4294967296），暂时无需调整。
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当前scn值
SCN = (SCN_Wrap * 4294967296）+ SCN_Base = ( 0 * 4294967296）+ 1455505 = 1455505


增加10w后的目标SCN
1455505 + 100000 = 1555505
转为16机制为 0x17B7A1
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[root@host-01 ~]# ps -ef |grep LOCAL=YES
oracle     639   535  0 00:21 ?        00:00:00 oracleorcl (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
root      1788  1754  0 00:23 pts/1    00:00:00 grep --color=auto LOCAL=YES


[oracle@host-01 ~]$ gdb $ORACLE_HOME/bin/oracle 639
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-120.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from u01/app/oracle/product/12.2.0/dbhome_1/bin/oracle...(no debugging symbols found)...done.
Attaching to program: u01/app/oracle/product/12.2.0/dbhome_1/bin/oracle, process 639
Reading symbols from u01/app/oracle/product/12.2.0/dbhome_1/lib/libodm12.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libodm12.so
Reading symbols from u01/app/oracle/product/12.2.0/dbhome_1/lib/libofs.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libofs.so
Reading symbols from u01/app/oracle/product/12.2.0/dbhome_1/lib/libcell12.so...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libcell12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libskgxp12.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libskgxp12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libskjcx12.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libskjcx12.so
Reading symbols from /lib64/librt.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/librt.so.1
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libmql1.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libmql1.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libipc1.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libipc1.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libclsra12.so...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libclsra12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libdbcfg12.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libdbcfg12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libhasgen12.so...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libhasgen12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libskgxn2.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libskgxn2.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libocr12.so...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libocr12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libocrb12.so...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libocrb12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libocrutl12.so...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libocrutl12.so
Reading symbols from /lib64/libaio.so.1...Reading symbols from /lib64/libaio.so.1...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Loaded symbols for /lib64/libaio.so.1
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libons.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libons.so
Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libm.so.6
Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Loaded symbols for /lib64/libpthread.so.0
Reading symbols from /lib64/libnsl.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnsl.so.1
Reading symbols from /lib64/libresolv.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libresolv.so.2
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/libgcc_s.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libgcc_s.so.1
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /usr/lib64/libnuma.so.1...Reading symbols from /usr/lib64/libnuma.so.1...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Loaded symbols for /usr/lib64/libnuma.so.1
Reading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnss_files.so.2
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libnque12.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libnque12.so
Reading symbols from /u01/app/oracle/product/12.2.0/dbhome_1/lib/libshpksse4212.so...(no debugging symbols found)...done.
Loaded symbols for /u01/app/oracle/product/12.2.0/dbhome_1/lib/libshpksse4212.so
0x00007f8e8d918740 in __read_nocancel () from /lib64/libpthread.so.0
Missing separate debuginfos, use: debuginfo-install glibc-2.17-326.el7_9.x86_64 libaio-0.3.109-13.el7.x86_64 libgcc-4.8.5-44.el7.x86_64 numactl-libs-2.0.9-7.el7.x86_64
(gdb)
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-- x86架构的gdb会自动处理小端序，因此直接写入0x17B7A1即可
(gdb) set *((int*) 0x0600113B8) = 0x17B7A1
(gdb) quit


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SQL> oradebug dumpvar sga kcsgscn_;
kcslf kcsgscn_ [0600113B8, 0600113E8) = 0017B7A1 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 60049740 00000000
-- 输出中应显示新的SCN Base值（0017B7A1）


-- 查看当前scn
SQL> SELECT current_scn FROM v$database;
CURRENT_SCN
-----------
   1555921
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alter database open;
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