Oracle Database identifier in short DBID is an internal, unique identifier for an Oracle database. Database administrator must note down the DBID in safe place, so that any miss-happening to the database could be easily identified and recovered. In case it is required to recover SPFILE or control file from autobackup, such as disaster recovery, you will need to set DBID. So lets see how to get DBID in NOMOUNT State.
Why DBID is important?
- It is an unique identifier for a database.
- In case of backup and recovery RMAN distinguishes databases by DBID.
- When DBID of a database is changed, all previous backups and archived logs of the database become unusable.
- After you change the DBID, you must open the database with the RESETLOGS option, which re-creates the online redo logs and resets their log sequence to 1
- You should make a backup of the whole database immediately after changing the DBID.
Let's take an example of getting it in nomount state:
First shut down the database using shut immediate command
SQL> shut immediate Database closed. Database dismounted. ORACLE instance shut down.Now startup database in nomount state
SQL> startup nomount ORACLE instance started. Total System Global Area 606806016 bytes Fixed Size 1376268 bytes Variable Size 402657268 bytes Database Buffers 197132288 bytes Redo Buffers 5640192 bytesYou can also set tracefile identifier for easily identification of tracefile.
SQL> alter session set tracefile_identifier=orahow; Session altered.Now, dump first ten block of datafile, because each block header contains dbid information.
SQL> alter system dump datafile 'D:\app\SantoshTiwari\oradata\TEST11\USERS01.DBF' 2 block min 1 block max 10; System altered.Now find the location of Trace file.
SQL> show parameter user_dump_destNAME TYPE VALUE
------------------------------------ ----------- ------------------------------
user_dump_dest string d:\app\santoshtiwari\diag\rdbm
Now search for Db ID inside the trace file. In Linux you can use cat command with grep to find it:
cat filename | grep Db id
Here you can see the dump here:
Start dump data block from file D:\APP\SANTOSHTIWARI\ORADATA\TEST11\USERS01.DBF minblk 1 maxblk 10
V10 STYLE FILE HEADER:
Compatibility Vsn = 186646528=0xb200000
Db ID=3561501508=0xd4483344, Db Name='TEST11'
Control Seq=3522=0xdc2, File size=640=0x280
File Number=4, Blksiz=8192, File Type=3 DATA
In simple you can also get it using v$database:
SQL> select name, dbid from v$database;
DBID is also displayed by the RMAN client when it starts up and connects to your database. Typical output follows:
SQL> host rman target /Recovery Manager: Release 22.214.171.124.0 - Production on Thu Nov 6 19:59:06 2014Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.connected to target database: TEST11 (DBID=3561501508)