ORACLE RAC : TERMINATING THE INSTANCE DUE TO ERROR 304

 After refreshing my QA database using RMAN DUPLICATE, my instance startup was failing with the below error

USER (ospid: 60897): terminating the instance due to error 304

Instance terminated by USER, pid = 60897

Wed Mar 06 02:14:34 2019

Starting ORACLE instance (normal)

Looking into the spfile, I noticed the database was pulling wrong instance_number and thread numbers even though the DB configuration was correct

$ srvctl config database -d oradb

Database unique name: oradb

Database name: oradb

Oracle home: /opt/app/oradb/oracle/product/11.2.0.4

Oracle user: oradb

Spfile: +oradb_DATA/oradb/spfileoradb.ora

Domain: db.abc.com

Start options: open

Stop options: immediate

Database role: PRIMARY

Management policy: AUTOMATIC

Server pools: oradb

Database instances: oradb1,oradb2

Disk Groups: oradb_DATA,oradb_FRA,oradb_REDO1,oradb_REDO2

Mount point paths: 

Services: oradb_1_2.db.abc.com,oradb_2_1.db.abc.com

Type: RAC

Database is administrator managed

From the pfile I created from the current spfile I could see 

*.instance_number=2

*.thread=2

To resolve this, bring down the complete database and just start the failing instance, in our case instance 1

srvctl start instance -d oradb -i oradb1

Once the instance is started, login to SQL and run below

SQL> alter system set instance_number=1 scope=spfile sid='oradb1';

System altered.

SQL> alter system set thread=1 scope=spfile sid='oradb1';

System altered.

SQL> alter system set undo_tablespace='UNDO01' sid='oradb1';

System altered.

shutdown the instance and start the complete database

SQL> shutdown immediate

srvctl start database -d oradb

Hope this resolves your issue.