Tuning

Biggest contributor to latency is the Garbage Collector
Areas of Tuning : Memory, Lock Contention, CPU Usage, I/O
Areas of Memory Tuning:
- Memory footprint tuning
- Allocation rate tuning
- GC tuning

Memory footprint tuning

It's all about ensuring that the GC has less work to do
One of the classic symptoms is the OutOfMemoryError
Why ? It can be too much data, or the data representation is "fat", or there is a memory leak in the app code
What is too much data ?
Look at the GC logs. Turn on the verbosegc option
Look at the Full GC messages : [Full GC $before->$after($total), $time secs]
If more memory can be added, add it.
Do we actually need ALL that data in memory, consider using techniques such as LRU cache & Soft References
Data representation itself
JVM object header is two machine words. i.e. new Object() will consume 16 bytes on a 64 bit JVM
Simplest possible array decl : new byte[0] will take 24 bytes : 16 + 4 bytes (length) + 4 (round off to next multiple of 8)
e.g. avoid usage of primitive Wrappers.
Also not possible to know how the libraries we use are implemented - unless they are profiled.