What is your development checklist for Java low-latency application?

Question

I would like to create comprehensive checklist for Java low latency application. Can you add your checklist here?

Here is my list
1. Make your objects immutable
2. Try to reduce synchronized method
3. Locking order should be well documented, and handled carefully
4. Use profiler
5. Use Amdhal's law, and find the sequential execution path
6. Use Java 5 concurrency utilities, and locks
7. Avoid Thread priorities as they are platform dependent
8. JVM warmup can be used
9. Prefer unfair locking strategy

As per my definition, low-latency application is tuned for every Milli-seconds.

Answer 1

Use StringBuilder instead of String when generating large Strings. For example queries.

Answer 2

Buy, read, and understand Effective Java. Also available online

Answer 3

Although immutability is good, it is not necessarily going to improve latency. Ensuring low-latency is likely to be platform dependent.

Other than general performance, GC tuning is very important. Reducing memory usage will help GC. In particular if you can reduce the number of middle-aged objects that need to get moved about - keep it object either long lived or short lived. Also avoid anything touching the perm gen.

Answer 4

avoid boxing/unboxing, use primitive variables if possible.

Answer 5

Another important idea is to get it working first, then measure the performance, then isolate any bottlenecks, then optimize them, then measure again to verify improvement.

As Knuth said, "premature optimization is the root of all evil".

Answer 6

Avoid context switching wherever possible on the message processing path Consequence: use NIO and single event loop thread (reactor)