Xms和Xmx是Java虚拟机(JVM)的标志:

Xms: initial and minimum JVM heap size Format: -Xms<size>[g|G|m|M|k|K] Default Size: -server mode: 25% of free physical memory, >=8MB and <= 64MB -client mode: 25% of free physical memory, >=8MB and <= 16MB Typical Size: -Xms128M -Xms256M -Xms512M Function/Effect: -> JVM start with allocate Xms size memory Xmx: maximum JVM heap size Format: -Xmx<size>[g|G|m|M|k|K] Default Size: <= R27.2 Windows: 75% of total physical memory up to 1GB Linux/Solaris: 50% of available physical memory up to 1GB >= R27.3 Windows X64: 75% of total physical memory up to 2GB Linux/Solaris X64: 50% of available physical memory up to 2GB Windows x86: 75% of total physical memory up to 1GB Linux/Solaris X86: 50% of available physical memory up to 1GB Typical Size: -Xmx1g -Xmx2084M -Xmx4g -Xmx6g -Xmx8g Function/Effect: -> JVM allow use maxium of Xmx size memory when exceed Xmx, will java.lang.OutOfMemoryError How to fix OutOfMemoryError ? exceed Xmx value eg: from -Xmx4g to -Xmx8g

更详细地

查看官方文档:-X命令行选项

Java 8的Xmssize(最小堆大小)占用物理内存的1/64以上，-Xmxsize(最大堆大小)占用物理内存的1/4以下。

你可以通过以下方法检查默认的Java堆大小:

在Windows中:

java -XX:+PrintFlagsFinal -version | findstr /i "HeapSize PermSize ThreadStackSize"

在Linux中:

java -XX:+PrintFlagsFinal -version | grep -iE 'HeapSize|PermSize|ThreadStackSize'

哪些系统配置设置会影响默认值?

机器的物理内存& Java版本。

Xms和Xmx是Java虚拟机(JVM)的标志:

Xms: initial and minimum JVM heap size Format: -Xms<size>[g|G|m|M|k|K] Default Size: -server mode: 25% of free physical memory, >=8MB and <= 64MB -client mode: 25% of free physical memory, >=8MB and <= 16MB Typical Size: -Xms128M -Xms256M -Xms512M Function/Effect: -> JVM start with allocate Xms size memory Xmx: maximum JVM heap size Format: -Xmx<size>[g|G|m|M|k|K] Default Size: <= R27.2 Windows: 75% of total physical memory up to 1GB Linux/Solaris: 50% of available physical memory up to 1GB >= R27.3 Windows X64: 75% of total physical memory up to 2GB Linux/Solaris X64: 50% of available physical memory up to 2GB Windows x86: 75% of total physical memory up to 1GB Linux/Solaris X86: 50% of available physical memory up to 1GB Typical Size: -Xmx1g -Xmx2084M -Xmx4g -Xmx6g -Xmx8g Function/Effect: -> JVM allow use maxium of Xmx size memory when exceed Xmx, will java.lang.OutOfMemoryError How to fix OutOfMemoryError ? exceed Xmx value eg: from -Xmx4g to -Xmx8g

更详细地

查看官方文档:-X命令行选项

对于IBM JVM，命令如下:

java -verbose:sizes -version

有关用于Java 8的IBM SDK的更多信息，请访问http://www-01.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/com.ibm.java.lnx.80.doc/diag/appendixes/defaults.html?lang=en

在Windows上，可以使用以下命令找出运行应用程序的系统上的默认值。

java -XX:+PrintFlagsFinal -version | findstr HeapSize

寻找选项MaxHeapSize(用于-Xmx)和InitialHeapSize(用于-Xms)。

在Unix/Linux系统上，您可以这样做

java -XX:+PrintFlagsFinal -version | grep HeapSize

我认为结果输出是以字节为单位的。

终于!

从Java 8u191开始，你现在有以下选项:

-XX:InitialRAMPercentage
-XX:MaxRAMPercentage
-XX:MinRAMPercentage

可用于按可用物理RAM的百分比来确定堆的大小。(这与安装的RAM比内核使用的少)。

有关更多信息，请参阅Java8 u191的发布说明。请注意，这些选项是在Docker标题下提到的，但实际上无论您是在Docker环境中还是在传统环境中，它们都适用。

MaxRAMPercentage的默认值是25%。这是极端保守的。

My own rule: If your host is more or less dedicated to running the given java application, then you can without problems increase dramatically. If you are on Linux, only running standard daemons and have installed RAM from somewhere around 1 Gb and up then I wouldn't hesitate to use 75% for the JVM's heap. Again, remember that this is 75% of the RAM available, not the RAM installed. What is left is the other user land processes that may be running on the host and the other types of memory that the JVM needs (eg for stack). All together, this will typically fit nicely in the 25% that is left. Obviously, with even more installed RAM the 75% is a safer and safer bet. (I wish the JDK folks had implemented an option where you could specify a ladder)

设置MaxRAMPercentage选项如下所示:

java -XX:MaxRAMPercentage=75.0  ....

请注意，这些百分比值是“double”类型，因此必须使用小数点指定它们。如果使用“75”而不是“75.0”，就会得到一个有点奇怪的错误。