>90% of upgrade related problems are performance issues after an upgrade.
Source: Oracle Corp
Oracle tools for helping you tune the database:
- Statspack - FREE - (See note 394937.1)
- SQL Plan Management - FREE - Part of Oracle 11g Enterprise Edition, no need for a license (https://blogs.oracle.com/optimizer/entry/does_the_use_of_sql).
- AWR - Diagnostics Pack & Tuning Pack license required.
- Real Application Testing (Features: SQL Performance Analyser & Database Replay) - Tuning Pack license required.
Since 11g, Oracle recommend, instead of: storing outlines, fixing stats, using SQL hints, using the Rule Based Optimiser (desupported); you should use the SQL Plan Management tool along with SQL Profiling.
See spm_white_paper_ow07.pdf for more information.