运行 JVM 的 GC 参数是什么?

What GC parameters is a JVM running with?(运行 JVM 的 GC 参数是什么?)

问题描述

我仍在调查我在 GC 调优方面遇到的问题(请参阅 之前的问题)，涉及大量阅读和实验.

I'm still investigating issues I have with GC tuning (see prior question), which involves lots of reading and experimentation.

Sun Java5+ JVM 尝试根据其环境自动选择最佳 GC 策略和参数，这很棒，但我不知道如何查询正在运行的 JVM 以找出这些参数是什么.

Sun Java5+ JVMs attempt to automatically select the optimal GC strategy and parameters based on their environment, which is great, but I can't figure out how to query the running JVM to find out what those parameters are.

理想情况下，我想看看虚拟机自动选择的各种与 GC 相关的 -XX 选项的值.如果我有这个，我可以有一个基线来开始调整.

Ideally, I'd like to see what values of the various GC-related -XX options are being used, as selected automatically by the VM. If I had that, I could have a baseline to begin tweaking.

有人知道从正在运行的 VM 中恢复这些值吗?

Anyone know to recover these values from a running VM?

推荐答案

查看HotSpotDiagnosticMBean

以下示例将打印出选项的值以及该值是 DEFAULT 还是 VM_CREATION:

The following example will print out the value of an option as well as whether the value is DEFAULT or VM_CREATION:

import java.lang.management.ManagementFactory;

import javax.management.ObjectName;
import javax.management.openmbean.CompositeData;
import javax.management.openmbean.CompositeDataSupport;

public class HotSpotTest {

    public static void main(String [] args) throws Exception {
        printHotSpotOption("MaxHeapFreeRatio");
        printHotSpotOption("SurvivorRatio");
        printHotSpotOptions();
    }

    private static void printHotSpotOption(String option) throws Exception {
        ObjectName name = new ObjectName("com.sun.management:type=HotSpotDiagnostic");
        String operationName = "getVMOption";
        Object [] params = new Object [] {option};
        String [] signature = new String[] {String.class.getName()};
        Object result = ManagementFactory.getPlatformMBeanServer().invoke(name, operationName, params, signature);
        CompositeDataSupport data = (CompositeDataSupport) result;

        System.out.println(option);
        System.out.println("- Value: "+data.get("value"));
        System.out.println("- Origin: "+data.get("origin"));
    }

    private static void printHotSpotOptions() throws Exception {
        ObjectName name = new ObjectName("com.sun.management:type=HotSpotDiagnostic");
        String attributeName = "DiagnosticOptions";
        Object result = ManagementFactory.getPlatformMBeanServer().getAttribute(name, attributeName);
        CompositeData [] array = (CompositeData[]) result;
        for (CompositeData d : array) {
            System.out.println(d.get("name"));
            System.out.println("- Value: "+d.get("value"));
            System.out.println("- Origin: "+d.get("origin"));
        }
    }
}

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