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https://www.happycoders.eu/java/compact-object-headers/
Compact Object Headers in Java (Page last updated April 2025, Added 2026-08-29, Author Sven Woltmann, Publisher HappyCoders). Tips:

• Compact Object Headers in JDK 27 requires no enabling flag; -XX:-UseCompactObjectHeaders is only a rollback option.
• Applications containing many small objects benefit most from Compact Object Headers.
• Compact Object Headers provides workload-dependent results: commonly 10-20% less heap, while one SPECjbb2015 configuration measured 22% less heap, 8% less CPU and 15% fewer collections.
• Compact Object Headers causes a four-byte reduction in the header but does not necessarily shrink every object because of eight-byte object alignment.
• Use JOL to compare representative object layouts, but use application-level heap, allocation, GC and throughput measurements before reducing production memory limits.

https://tschatzl.github.io/2026/08/10/jdk27-g1-serial-parallel-gc-changes.html
JDK 27 G1,Parallel,Serial GC changes (Page last updated August 2026, Added 2026-08-29, Author Thomas Schatzl, Publisher tschatzl@github). Tips:

• Benchmark G1 against -XX:+UseSerialGC in constrained deployments; G1 is a better default, but not universally faster so you may be better explicitly setting serial GC for specific configurations.
• Measure throughput, tail latency, startup and total RSS under the real container limits.
• In JDK 27 G1's MinHeapFreeRatio/MaxHeapFreeRatio defaults change from 40/70 to 0/100, preventing counterproductive resizing after Full GCs.
• In JDK 27 Parallel GC improves adaptive tenuring and heap expansion under repeated large allocations.
• In JDK 27 all collectors improve TLAB sizing for workloads creating many short-lived, lightly allocating threads.

Jack Shirazi Back to newsletter 309 contents