Java Performance Update 2024 by Per Minborg

Performance gains and optimizations in Java 24/25 include merge store operations, improved loop unrolling, auto vectorization, and better memory segment handling

Memory segments (part of Foreign Function & Memory API) provide significant performance benefits by allowing operations on larger chunks of data (64-bit, 256-bit or more) instead of byte-by-byte processing

Use JMH (Java Microbenchmark Harness) for proper performance testing - it handles warm-up phases, prevents JVM optimizations from skewing results, and provides proper error margins and statistics

Don’t use laptops for performance benchmarking - factors like CPU throttling, power management, and heat can significantly impact results. Use dedicated servers instead.

The new generational ZGC garbage collector (default in JDK 24) provides better performance for large heaps up to terabyte sizes with minimal stop-the-world events

Performance metrics should consider multiple factors beyond just throughput:

• Startup time and warm-up periods
• Memory usage and cache efficiency
• Power consumption and CPU utilization
• Worst-case latency scenarios
• Resource contention

Object headers optimization (Project Lilliput) reduces memory usage by 20-30% by shrinking object headers from 128 bits to 64 bits

Native code isn’t always faster than Java - in many cases Java can match or exceed native performance, especially after JIT compilation and optimization

Proper performance testing requires:

• Adequate warm-up periods (thousands of iterations)
• Testing on supported platforms/architectures
• Consideration of GC, thread pools, and CPU core count
• Using System.nanoTime() instead of currentTimeMillis()

Future improvements will focus on auto vectorization, virtual thread handling, and better startup performance through ahead-of-time compilation