J2EE Application Performance QA and Tuning

To start J2EE application performance QA and tuning:

Set a goal:

Before you begin tuning your J2EE application’s performance, set a goal. Often this goal addresses the maximum concurrent users the application will support for a given limit on response times. But the goal can also focus on other variables – for example, the response times should not increase more than 10 percent during the peak hour of user load.

Identify problem areas:

It is important to identify the bottlenecks when you start making changes to improve performance. A little investigation into problems might reveal the specific component that causes poor performance. For example, if the CPU usage on an application server is high, you will want to focus on tuning the application server first.

Follow a methodical and focused path:

Once the goal is set, try to make changes that are expected to have the biggest impact on performance. Your time is better spent tuning a method that takes 10 seconds but gets called 100 times than tuning a method that takes one minute but gets called only once. In an ideal world, you test one change at a time before using it in a production environment. You make one change and stress-test it. If the change results in positive impact, only then will you make it permanent.

Performance planning for managers:

Balancing Network Load with Priority Queues Tips:

My query was fine last week and now it is slow. Why?

The likely cause of this is because the execution plan has changed. Generate a current explain plan of the offending query and compare it to a previous one that was taken when the query was performing well. Usually the previous plan is not available.

Some factors that can cause a plan to change are:

What do you think the plan should be? Run the query with hints to see if this produces the required performance.

It can also happen because of a very high high water mark. Typically when a table was big, but now only contains a couple of records. Oracle still needs to scan through all the blocks to see if they contain data.

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