ORACLE startup upgrade failed with ORA-27041 ORA-15025

ORACLE DB - Upgrade from 11.2.0.3 to 11.2.0.4

Startup upgrade failed with ORA-27041 ORA-15025 in 11.2.0.4.

However we were able to start DB from old (11.2.0.3) home. 

After spending sometime we were able to fix it by changing ownership like below.

[grid@Node02 ~]$ ls -l /u01/app/oracle/product/11.2.0.4/bin/oracle

-rwsr-s--x 1 oracle oinstall 239772898 Aug 25 05:25 /u01/app/oracle/product/11.2.0.4/bin/oracle

[grid@Node02 ~]$  setasmgidwrap o=/u01/app/oracle/product/11.2.0.4/bin/oracle

[grid@Node02 ~]$ ls -l /u01/app/oracle/product/11.2.0.4/bin/oracle

-rwsr-s--x 1 oracle asmadmin 239772898 Aug 25 05:25 /u01/app/oracle/product/11.2.0.4/bin/oracle

RMAN Incremental Backups to Roll Forward a Physical Standby Database

* DataGuard setup between primary and standby databases - ORACLE 11gR2

* Some of the archive logs  in primary were deleted accidentally and these were noto shipped to Standby. We realized it after 3 days.

* We followed the approach mentioned in below link by just taking incremental backup in primary to rollforward standby database.

https://docs.oracle.com/cd/B19306_01/server.102/b14239/scenarios.htm#CIHIAADC

ORA-01555 on Standby

DB - 11gR2

Users were running select queries on Primary where as the same select was failing with ORA-01555 in Active standby. 

Undo_retention =   900 sec --Primary
Undo_retention = 21600 sec --Standby

Inspite of higher retention at standby users were facing ORA-01555. 

Later realized that undo_retention at stantby does not have any significance. Oracle Dataguard just replicates the undo_retention value from Primary. Increased the Undo_retention in Primary to get rid of this error.

Below note  really helped in understanding this.
http://alexeymoseyev.wordpress.com/2013/10/24/ora-01555-on-standby/

ORA-12502: TNS:listener received no CONNECT_DATA from client.

Users were able to connect from One client where as they were having issues from another client.
Jobs were failing with ORA-12502 error.

This is RAC env. 11gR2

From both clients
1. we can telnet,ping to db hosnames
2. we can telnet,ping to scan

however telnet to VIP was not working for problematic client. Informed apps team to Open firewall request for VIPs from client. This resolved the issue.

Below two links helped me in troubleshooting the issue.

http://levipereira.wordpress.com/2011/05/03/configuring-client-to-use-scan-11-2-0/
http://stelliosdba.blogspot.sg/2012/02/ora-12502-tnslistener-received-no.html