Found an interesting way to determine the database id (dbid) from the system data file.
The method comes from location 9758 of the Kindle edition of RMAN Recipes for Oracle Database 12c: A Problem-Solution Approach (2nd Ed.) by Darl Kuhn, Sam R. Alapati, and Arup Nanda. It was published by A-Press in 2013.
The method is as follows:
C:\Users\Douglas.RYDE>sqlplus / as sysdba SQL*Plus: Release 220.127.116.11.0 Production on Mon Oct 28 19:58:04 2013 Copyright (c) 1982, 2013, Oracle. All rights reserved. Connected to: Personal Oracle Database 12c Release 18.104.22.168.0 - 64bit Production With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options SQL> oradebug setmypid Statement processed. SQL> alter system dump datafile 'D:\APP\ORACLE\ORADATA\RYDE\SYSTEM01.DBF' block min 1 block max 10; System altered. SQL> oradebug tracefile_name D:\APP\ORACLE\diag\rdbms\ryde\ryde\trace\ryde_ora_535848.trc SQL>
The contents of the trace file includes the following:
*** 2013-10-28 19:43:49.218 Start dump data block from file D:\APP\ORACLE\ORADATA\RYDE\SYSTEM01.DBF minblk 1 maxblk 10 V10 STYLE FILE HEADER: Compatibility Vsn = 202375168=0xc100000 Db ID=3524156584=0xd20e5ca8, Db Name='RYDE' Activation ID=0=0x0 Control Seq=32662=0x7f96, File size=101120=0x18b00 File Number=1, Blksiz=8192, File Type=3 DATA
This says that the dbid of my database is 3524156584. I can confirm this by the following query:
SELECT dbid FROM v$database;
The result is:
DBID ---------- 3524156584
Note: If you try the following command instead:
alter system dump datafile 1 block min 1 block max 10;
The trace file will show the following message:
*** 2013-10-28 19:58:33.046 Start dump data blocks tsn: 0 file#:1 minblk 1 maxblk 10 Block 1 (file header) not dumped:use dump file header command Block dump from cache: