What is the first performance tuning task to be performed once a performance issue is raised in an oracle database?

Pull AWR report and do load analysis , instance activity and top sql performance

1. Chek list of connected users2. Check system memory, system processes and DB space utilization

3. Check ong running queries from SQL

4. Check blocking queries and possible deadlocks

5. Extract AWR report and analyse for SQL statements genarally running for too long and use explaing plan to analyse query for better performance

Check out the previous explain plan(if available) else check the current explain plan, trace file or AWR for finding the performance bottlenecks

Listing down some general performance tuning taks.

1. Loops : Check if you are running any un-necessary loops and try to restrict them.

2. Restrict usage of calculations in Joins and Where clauses.

3. Check for Indexes

4. Remove un-necessary columns/tables, try to work with smallest data set possible.

5. Use concepts like bulk Collect, For All for faster record processing.

Automatic Tuning Optimizer.