java垃圾回收日志条目是否“Full GC(系统)"?意思是一些名为 System.gc() 的类?

Does java garbage collection log entry quot;Full GC (System)quot; mean some class called System.gc()?(java垃圾回收日志条目是否“Full GC(系统)?意思是一些名为 System.gc() 的类?)

问题描述

垃圾收集日志中的Full GC (System)"条目是什么意思?那个叫 System.gc() 的类?

What does "Full GC (System)" entry in the garbage collection logs mean? That some class called System.gc() ?

我的垃圾收集日志有两种不同的完整 gc"条目类型?一个带有系统"一词，另一个没有.有什么区别?

My garbage collection logs has two different entry types for 'full gc'? One with the word 'System', the other without. What's the difference?

(更新:我搜索了这个词并没有找到明确的答案，只有几个问题.所以我想我会发布它.

(Update: I searched on this term and didn't find a definitive answer, only a few questions. So I thought I'd post it).

系统:

164638.058:[Full GC (系统) [PSYoungGen:22789K->0K(992448K)][PSOldGen:1645508K->1666990K(2097152K)]1668298K->1666990K(3089600K)[PSPermGen:164914K->164914K(166720K)], 5.7499132秒] [时间:用户=5.69 系统=0.06，真实=5.75 秒]

164638.058: [Full GC (System) [PSYoungGen: 22789K->0K(992448K)] [PSOldGen: 1645508K->1666990K(2097152K)] 1668298K->1666990K(3089600K) [PSPermGen: 164914K->164914K(166720K)], 5.7499132 secs] [Times: user=5.69 sys=0.06, real=5.75 secs]

无系统:

166687.013: [完整 GC [PSYoungGen: 126501K->0K(922048K)] [PSOldGen:2063794K->1598637K(2097152K)]2190295K->1598637K(3019200K)[PSPermGen:165840K->164249K(166016K)], 6.8204928秒] [时间:用户=6.80 系统=0.02，真实=6.81 秒]

166687.013: [Full GC [PSYoungGen: 126501K->0K(922048K)] [PSOldGen: 2063794K->1598637K(2097152K)] 2190295K->1598637K(3019200K) [PSPermGen: 165840K->164249K(166016K)], 6.8204928 secs] [Times: user=6.80 sys=0.02, real=6.81 secs]

GC 选项

我们与 gc 相关的 java 内存选项有:-Xloggc:../server/pe/log/jvm_gc.log -XX:+PrintGCTimeStamps -XX:+PrintGCDetails

Our gc-related java memory options are: -Xloggc:../server/pe/log/jvm_gc.log -XX:+PrintGCTimeStamps -XX:+PrintGCDetails

我们不使用'-XX:+DisableExplicitGC'，所以可能某些错误的类确实调用了 System.gc()

We do not '-XX:+DisableExplicitGC', so it's possible some errant class does call System.gc()

fwiw，我们完整的 jvm 选项:

fwiw, our full jvm options:

-Xms3072m -Xmx3072m -XX:+HeapDumpOnOutOfMemoryError -XX:-UseGCOverheadLimit -Xloggc:../server/pe/log/jvm_gc.log -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -XX:MaxPermSize=256m -XX:+UseCompressedOops

-Xms3072m -Xmx3072m -XX:+HeapDumpOnOutOfMemoryError -XX:-UseGCOverheadLimit -Xloggc:../server/pe/log/jvm_gc.log -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -XX:MaxPermSize=256m -XX:+UseCompressedOops

提前致谢，

会

推荐答案

从 OpenJDK 的源代码我会说是

From the source for OpenJDK I would say it is

const bool is_system_gc = gc_cause == GCCause::_java_lang_system_gc;

// This is useful for debugging but don't change the output the
// the customer sees.
const char* gc_cause_str = "Full GC";
if (is_system_gc && PrintGCDetails) {
  gc_cause_str = "Full GC (System)";
}

我创建了一个自定义版本的 Runtime 类，以便在调用 Runtime.getRuntime().gc() 时将线程名称和堆栈跟踪记录到一个文件中.(System.gc() 调用它)我发现它在跟踪和删除此类调用者方面很有用.

I created a custom version of the Runtime class to record the thread name and stack trace to a file whenever Runtime.getRuntime().gc() was called. (System.gc() calls this) I found it useful in tracking down and removing such callers.

发生这种情况的一个地方是 sun.misc.GC 类.RMI 将要求该类确保在最后 N 秒内执行了 GC.如果没有 GC，则会触发 full GC.

One place this happens is in sun.misc.GC class. The RMI will ask this class to ensure a GC has been performing in the last N seconds. If there has been no GC it triggers a full GC.

这仅在您减少次要 GC 的数量时才会显示为问题.具有讽刺意味的是，这可能意味着您获得更多完整的 GC.;)

This only shows as a problem if you reduce the number of minor GCs. Ironicly it can mean you get more full GCs. ;)

我不使用 RMI(也许 JConsole 除外)所以我将它设置为一周.(认为​​默认是一个小时)

I don't use RMI (except perhaps JConsole) So I have it set to a week. (Think the default is an hour)

-Dsun.rmi.dgc.server.gcInterval=604800000
-Dsun.rmi.dgc.client.gcInterval=604800000

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