第二篇 JVM性能调优之实战内存溢出

本文阅读量: 2019-04-08

一 jstat查看虚拟机统计信息

命令格式：

$ jstat -help
Usage: jstat -help|-options
       jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]

Definitions:
  <option>      An option reported by the -options option
  <vmid>        Virtual Machine Identifier. A vmid takes the following form:
                     <lvmid>[@<hostname>[:<port>]]
                Where <lvmid> is the local vm identifier for the target
                Java virtual machine, typically a process id; <hostname> is
                the name of the host running the target Java virtual machine;
                and <port> is the port number for the rmiregistry on the
                target host. See the jvmstat documentation for a more complete
                description of the Virtual Machine Identifier.
  <lines>       Number of samples between header lines.
  <interval>    Sampling interval. The following forms are allowed:
                    <n>["ms"|"s"]
                Where <n> is an integer and the suffix specifies the units as
                milliseconds("ms") or seconds("s"). The default units are "ms".
  <count>       Number of samples to take before terminating.
  -J<flag>      Pass <flag> directly to the runtime system.

命令详细说明参考官方文档：
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstat.html#BEHHGFAE

类加载信息查看

jstat -class …

$ jps
57184 Jps
18386
14837
54214 Launcher
54215 ImServerApplication
54670
$ jstat -class 54215 1000 10
Loaded  Bytes  Unloaded  Bytes     Time
  6901 12563.6        1     0.9       2.58
  6901 12563.6        1     0.9       2.58
  6901 12563.6        1     0.9       2.58

命令解释 jstat -class 54215 1000 10

54215 是PID

1000 是间隔时间1000毫秒

10 是输出十次

输出信息说明：

Class loader statistics.

Loaded: Number of classes loaded.

Bytes: Number of kBs loaded.

Unloaded: Number of classes unloaded.

Bytes: Number of Kbytes unloaded.

Time: Time spent performing class loading and unloading operations.

垃圾收集信息

options 有 -gc、-gcutil、-gccause、-gcnew、-gcold

$ jstat -gc 58589 1000 3
 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT
 0.0   8192.0  0.0   8192.0 73728.0  26624.0   49152.0    18432.0   35840.0 33898.7 4864.0 4466.1      6    0.068   0      0.000    0.068
 0.0   8192.0  0.0   8192.0 73728.0  27648.0   49152.0    18432.0   35840.0 33898.7 4864.0 4466.1      6    0.068   0      0.000    0.068
 0.0   8192.0  0.0   8192.0 73728.0  27648.0   49152.0    18432.0   35840.0 33898.7 4864.0 4466.1      6    0.068   0      0.000    0.068

-gc option

Garbage-collected heap statistics.

S0C: Current survivor space 0 capacity (kB).

S1C: Current survivor space 1 capacity (kB).

S0U: Survivor space 0 utilization (kB).

S1U: Survivor space 1 utilization (kB).

EC: Current eden space capacity (kB).

EU: Eden space utilization (kB).

OC: Current old space capacity (kB).

OU: Old space utilization (kB).

MC: Metaspace capacity (kB).

MU: Metacspace utilization (kB).

CCSC: Compressed class space capacity (kB).

CCSU: Compressed class space used (kB).

YGC: Number of young generation garbage collection events.

YGCT: Young generation garbage collection time.

FGC: Number of full GC events.

FGCT: Full garbage collection time.

GCT: Total garbage collection time.

JVM内存结构图

堆区

yong (S0、S1、Eden)

old

非堆区Metaspace

CCS - 启用了短指针时的压缩类空间

CodeCache - JIT的代码信息把Java代码转化为Native代码 jni代码等

JIT编译信息

options 有 -compiler -printcompilation

-compiler option

Java HotSpot VM Just-in-Time compiler statistics.

Compiled: Number of compilation tasks performed.

Failed: Number of compilations tasks failed.

Invalid: Number of compilation tasks that were invalidated.

Time: Time spent performing compilation tasks.

FailedType: Compile type of the last failed compilation.

FailedMethod: Class name and method of the last failed compilation.

二 jmap+MAT实战内存溢出

实战堆内存溢出

先设置JVM参数 -Xmx32M -Xmx32M
再调用SpringBoot的一个Contoller方法如下：

import com.jacky.imserver.entity.User;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

@RestController
@RequestMapping("/user")
public class UserController {

    private List<User> users = new ArrayList<>();

    @GetMapping("/list")
    public void list() {
        for (int i = 0; ; i++) {
            users.add(new User(i + "", UUID.randomUUID().toString(), "用户" + i));
        }
    }

}

最终会报异常 java.lang.OutOfMemoryError: Java heap space

实战非堆内存溢出

1 编写内存溢出代码

先设置JVM参数 -XX:MetaspaceSize=32M -XX:MaxMetaspaceSize=32M

使用asm生成class
asm库的依赖

<!-- https://mvnrepository.com/artifact/asm/asm -->
<dependency>
    <groupId>asm</groupId>
    <artifactId>asm</artifactId>
    <version>3.3.1</version>
</dependency>

执行的代码


import com.jacky.imserver.utils.GenerateClassUtil;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.ArrayList;
import java.util.List;

@RestController
@RequestMapping("/user")
public class UserController {

    private List<Class> classes = new ArrayList<>();

    @GetMapping("/noheap")
    public void noheap() {
        for (int i = 0; ; i++) {
            classes.add(GenerateClassUtil.generateHelloClass(i));
        }
    }

}

生成类的工具类

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public class GenerateClassUtil extends ClassLoader implements Opcodes {
    public static Class<?> generateHelloClass(int index) {

        // 定义一个叫Test的类
        ClassWriter classWriter = new ClassWriter(0);
        String name = "Test" + index;

        classWriter.visit(V1_1, ACC_PUBLIC, name, null, "java/lang/Object", null);
        // 生成默认构造
        MethodVisitor mv = classWriter.visitMethod(ACC_PUBLIC,
                "<init>",
                "()V",
                null,
                null);
        // 生成构造方法的字节码指令
        mv.visitVarInsn(ALOAD, 0);

        mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V");
        mv.visitInsn(RETURN);
        mv.visitEnd();

        // 生成main方法
        mv = classWriter.visitMethod(ACC_PUBLIC + ACC_STATIC,
                "main",
                "([Ljava/lang/String;)V",
                null,
                null);
        mv.visitFieldInsn(GETSTATIC,
                "java/lang/System",
                "out",
                "Ljava/io/PrintStream;");
        mv.visitLdcInsn("Hello world!");
        mv.visitMethodInsn(INVOKEVIRTUAL,
                "java/io/PrintStream",
                "println",
                "(Ljava/lang/String;)V");
        mv.visitInsn(RETURN);
        mv.visitMaxs(2, 2);

        byte[] code = classWriter.toByteArray();
        return new GenerateClassUtil().defineClass(name, code, 0, code.length);
    }
}

会抛出异常 java.lang.OutOfMemoryError: Metaspace

2 导出内存映像文件

内存溢出自动导出

-XX:+HeapDumpOnOutOfMemoryError

-XX:HeapDumpPath=./
使用jmap命令手动导出

$ jmap -heap
Usage:
    jmap [option] <pid>
        (to connect to running process)
    jmap [option] <executable <core>
        (to connect to a core file)
    jmap [option] [server_id@]<remote server IP or hostname>
        (to connect to remote debug server)

where <option> is one of:
    <none>               to print same info as Solaris pmap
    -heap                to print java heap summary
    -histo[:live]        to print histogram of java object heap; if the "live"
                         suboption is specified, only count live objects
    -clstats             to print class loader statistics
    -finalizerinfo       to print information on objects awaiting finalization
    -dump:<dump-options> to dump java heap in hprof binary format
                         dump-options:
                           live         dump only live objects; if not specified,
                                        all objects in the heap are dumped.
                           format=b     binary format
                           file=<file>  dump heap to <file>
                         Example: jmap -dump:live,format=b,file=heap.bin <pid>
    -F                   force. Use with -dump:<dump-options> <pid> or -histo
                         to force a heap dump or histogram when <pid> does not
                         respond. The "live" suboption is not supported
                         in this mode.
    -h | -help           to print this help message
    -J<flag>             to pass <flag> directly to the runtime system

dump出来的例子：

1
2
3

$ jmap -dump:format=b,file=heap.hprof 60899
Dumping heap to /Users/jacky/heap.hprof ...
Heap dump file created

3 MAT(Memory Analyzer)分析内存

使用MAT分析工具 File -> open File 打开上面dump出来的hprof内存映像文件

打开后看到如下信息，从信息中会给出内存泄漏原因：
(另外还可以从其他维度去定位是哪个类导致的内存泄漏)

Leak Suspects

System Overview

 Leaks

 【这里有一个饼图，已省略】


  Problem Suspect 1

One instance of "com.jacky.imserver.controller.UserController" loaded by "org.springframework.boot.devtools.restart.classloader.RestartClassLoader @ 0x7fb2e5e28" occupies 18,098,216 (60.00%) bytes. The memory is accumulated in one instance of "java.lang.Object[]" loaded by "<system class loader>".

Keywords
java.lang.Object[]
com.jacky.imserver.controller.UserController
org.springframework.boot.devtools.restart.classloader.RestartClassLoader @ 0x7fb2e5e28

Details »
  Problem Suspect 2

5,199 instances of "java.lang.Class", loaded by "<system class loader>" occupy 4,543,056 (15.06%) bytes.

Keywords
java.lang.Class

Details »