A quick checklist for Oracle upgrade 9i To 10gR2

1. Take a consistent backup of your database.
2. Install Oracle 10gR2
3. Check objects status in the db.
Compile invalid objects.
@?/rdbms/admin/ utlrp.sql
4. Create SYSAUX tablespace.
A manadatory requirement for Oracle 10G
5. Run utlu102i.sql script which checks the db readiness to upgrade to 10g.
This script will be available in oracle10g home. So specify complete path for oracle 10g rdbms/admin directory
6. Shutdown immediate the database.
7. Copy the parameter file & password file from existing home to new Oracle 10g Home.
8. Edit oratab and rerun oraenv to bring the changes in affect.
Oratab would be in /etc/oratab OR /var/opt/oracle/oratab
9. Startup the database in upgrade mode.
Command: startup upgrade
10. Now upgrade for which run catupgrd script. Spool the output.
This can take upto 40 mins to complete.
@?/rdbms/admin/catupgrd.sql
11. Now recompile invalid objects.
Run utlrp.sql
Remember to compare the status of objects with the one before upgrade. Current should be same or Less.
12. Check the status of upgrade
@?/rdbms/admin/utlu102s.sql
13. Alter / reset the parameter file and set the compatibility parameter.

The upgrade of Oracle 9i To 10g is completed successfully.

For further detailed reading refer Oracle documentation & metalink docs.
Useful read about Optimizer stats while upgrading:
http://optimizermagic.blogspot.com/2008/02/upgrading-from-oracle-database-9i-to.html

Metalink Doc: Complete Checklist for Manual Upgrades to 10gR2 [ID 316889.1]

Performance statistics of database

Interestingly, maybe not surprisingly, we tend to let certain things go in background since, we are not using/doing that action as part of our daily work .I am grateful to Syed who pushed me to move from my comfort zone.
Preserving performance data in different Oracle versions...
Oracle 9i=> Performance statistics of a database was generally created in perfstat schema. So all we had to do was export user perfstat data and this dumpfile could be used for importing in another database in case required for analysis.
Oracle 10g=> introduced a few new reports and performance statistics was by default enabled to take snapshots every hour. Automatic Workload Repository (AWR) for cumulative and delta values at all levels except session & active session history (ASH) for the current state of all active sessions. By default we have snapshots of the performance data once every hour and the statistics are retained in the workload repository for 7 days.
To preserve this performance data, we gotta use "awrextr.sql" script to extract data into a data pump export file and "awrload.sql" script to load this data from dump file.
Oracle 11g=> The same system holds. A few enhancements are of course seen. So, to preserve this Oracle database performance data, we gotta use "awrextr.sql" script to extract data into a data pump export file and "awrload.sql" script to load this data from dump file.