asmhatreandClaude Sonnet 5
2f88734f5d
MaxRAMPercentage vs a hardcoded -Xmx, -XX:-UseContainerSupport, the ActiveProcessorCount lie, and which diagnostic flags are worth leaving on in prod, verified in real Docker containers on JDK 25 and JDK 27. Co-Authored-By: Claude Sonnet 5 <[email protected]>
38 lines
1.6 KiB
Java
38 lines
1.6 KiB
Java
import java.util.ArrayList;
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import java.util.List;
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/**
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* Deliberately allocates and retains heap in fixed-size chunks until it is
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* killed or finishes, printing progress as it goes. Used to demonstrate what
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* actually happens when a container's memory limit, the JVM's heap flags,
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* and real allocation pressure disagree with each other. See the post at
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* https://ankurm.com/jvm-flags-for-spring-boot-in-containers-jdk-25-27/
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* and docs/output/05-oom-*.txt / 06-oom-*.txt for the captured runs.
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*/
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public class MemoryHog {
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public static void main(String[] args) throws Exception {
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int chunkMb = args.length > 0 ? Integer.parseInt(args[0]) : 16;
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int sleepMs = args.length > 1 ? Integer.parseInt(args[1]) : 150;
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List<byte[]> held = new ArrayList<>();
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long totalMb = 0;
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System.out.println("MemoryHog starting: chunk=" + chunkMb + "MB sleep=" + sleepMs + "ms");
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System.out.flush();
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while (true) {
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byte[] chunk = new byte[chunkMb * 1024 * 1024];
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for (int i = 0; i < chunk.length; i += 4096) {
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chunk[i] = 1; // touch each page so it is actually resident, not just reserved
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}
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held.add(chunk);
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totalMb += chunkMb;
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Runtime rt = Runtime.getRuntime();
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System.out.printf("held=%dMB heapUsed=%dMB heapMax=%dMB freeHeap=%dMB%n",
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totalMb,
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(rt.totalMemory() - rt.freeMemory()) / (1024 * 1024),
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rt.maxMemory() / (1024 * 1024),
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rt.freeMemory() / (1024 * 1024));
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System.out.flush();
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Thread.sleep(sleepMs);
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}
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}
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}
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