Symptoms of low performing SQL

1. Consume high CPU, buffer, I/O, PGA memory 
2. Long running SQL or significantly different runtime 
3. High I/O, CPU ,memory, network waits
4. SQl consuming high DB time ( can be analysed using AWR, ASH )
5. Long running SQLs and operations 
6. SQL with execution plan change ( need to enable trace to see these using sqlplus)