Firing query inside a loop is a sin

Please donot fire a query inside a loop.Otherwise the performance problem your application will face is unimaginable. There is ALWAYS a way around.You can always solve the problem by firing the query outside the loop(using 'join' or 'in' statement or whatever).It doesn't matter if you need to write a complex and lengthy code to solve the problem by firing the query outside the loop.But please please don't fire it inside the loop.Otherwise almighty(a.k.a customer) will never forgive you.

Note:Be careful while using 'in' statement.If tokens inside the 'in' exceeds 490 in number,yacc Overflow Exception will occur. But there is a smart way around. Refer to following Robin's post.

Excessive Logging Sucks up Application Performance

I have seen some people performing logging operation unnessasarily.According to them,logging helps to idenify bugs quickly.But excessive use of logging can have a very serious impact on the performance of the application.I think if some errors occour,then those can be easily detected by logging the exception stacktrace.So I think,logging only stack trace info in catch section (java code) can help in improving performance a lot(most of the bugs can be traced from the error stack).Also , logging start and end of methods gives a good idea about the program flow.Apart from that logging should be avoided as much as possible because logging requires disk access which is always an expensive operation in terms of performance.