DO's & DONT's for a better application performance

Question

I am very new to tuning. What are the sql & pl/sql do's and dont's and best sql & pl/sql practices for a better application performance?
I was told by somebody to check explain plan for tuning db & sql statements. But i am bit confused by seeing the explain and don't know from where i have start and what i have take into consideration from explain plan to improve application preformance?
Can somebody help me in this regard?

Answer 1

> I am very new to tuning.
Good. Not having to tune means that the code is performing as it should.
And this is THE MOST IMPORTANT CONSIDERATION.
Do not write and design code that needs to be tuned and twisted and modded in order to perform. Write and design code with the core requirements of that code being:
- performance
- scalability
- flexibility
- maintainability
Good design = good code = good performance
No amount of tuning can turn bad code and a bad design into a well performing and scalable system. Which is why I dislike the concept of "tuning code". Start with a good and solid design. In other words, tune that before the code.
> What are the sql & pl/sql do's and dont's and best sql & pl/sql practices
for a better application performance?
The 1st basic rule is actually quite simple.
The "data layer" rule: Maximize SQL. Minimize PL/SQL.
Do not do in PL/SQL what SQL is very capable of doing. Fact. No other language is faster and better than SQL at crunching data in the Oracle RDBMS.
The 2nd basic rule is a logical extension of the 1st.
The "application layer" rule. Maximize PL/SQL. Minimize Java/C++/C#/Delphi/VB/etc.
Do not do in a 3rd party language what PL/SQL is extremely capable of doing. Fact. No 3rd party language is as capable as crunching data in the Oracle RDBMS as PL/SQL.
Stick to these two fundamental rules and your Oracle application will have a solid foundation for being a well performing and very scalable solution.