Claude
e83c9949d8
Spring Boot 4.1.1 catalog service measured on JDK 25, 26 and 27: live heap 320 MB to 273 MB with compact headers, per-class bytes per instance, container-sizing sweeps with real cgroup limits, 1-CPU Serial vs G1 with Native Memory Tracking, removed flags (MaxRAM, UseCompressedClassPointers), and a kernel OOM-kill check. Outputs in jdk27-memory/output. Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a
37 lines
1.5 KiB
Java
37 lines
1.5 KiB
Java
import java.lang.reflect.Field;
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/**
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* Where does the first field of an object start? Code that hard-codes "12 bytes of header" gets this wrong
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* on JDK 27. Run with: java --sun-misc-unsafe-memory-access=allow Offsets.java
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* (The flag silences the JDK 24+ warning about sun.misc.Unsafe; nothing here reads or writes memory.)
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*/
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public class Offsets {
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static class P {
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long id;
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int priceCents;
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int stock;
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boolean active;
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Object sku;
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}
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@SuppressWarnings("removal")
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public static void main(String[] args) throws Exception {
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Field f = sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
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f.setAccessible(true);
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sun.misc.Unsafe u = (sun.misc.Unsafe) f.get(null);
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System.out.println("java " + System.getProperty("java.version")
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+ " compact headers: " + java.lang.management.ManagementFactory
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.getPlatformMXBean(com.sun.management.HotSpotDiagnosticMXBean.class)
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.getVMOption("UseCompactObjectHeaders").getValue());
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long first = Long.MAX_VALUE;
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for (Field x : P.class.getDeclaredFields()) {
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long off = u.objectFieldOffset(x);
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first = Math.min(first, off);
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System.out.printf(" %-11s offset %2d%n", x.getName(), off);
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}
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System.out.println(" first field starts at byte " + first + " (so the header is at most " + first + " bytes)");
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System.out.println(" a hard-coded 12-byte header would be " + (first == 12 ? "right" : "WRONG") + " here");
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}
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}
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