When query is taking too long time

Question

When query is taking too long time,Where and how to start tuning it?
Here i've listed few things need to be considered,out of my knowledge and understanding
1.What the sql is waiting for(wait events)
2.Parameter modification need to be done at system/session level
3.The query has to be tuned (using hints )
4.Gathering/deleting statistics
List out any other things that need to be taken into account?
Which approach must be followed and on what basis that approach must be considered?

Answer 1

When query is taking too long time,Where and how to start tuning it?explain plan will be good start . trace also
Here i've listed few things need to be considered,out of my knowledge and understanding
1.What the sql is waiting for(wait events)When Oracle executes an SQL statement, it is not constantly executing. Sometimes it has to wait for a specific event to happen befor it can proceed.
Read
http://www.adp-gmbh.ch/ora/tuning/event.html
2.Parameter modification need to be done at system/session levelDepend on parameter , define parameter , trace done on session level for example
3.The query has to be tuned (using hints )Could be help you but you must know how to use .
4.Gathering/deleting statisticsDo it in non working hours , it will impact on database performance , but its good
List out any other things that need to be taken into account?Which account ?
Which approach must be followed and on what basis that approach must be considered?you could use lot of tools , Trace , AWR