Default Xmxsize in Java 8 max heap size

Question

In the oracle documentation I found      -Xmxsize Specifies the maximum size  in bytes  of the memory allocation pool in bytes     The default   value is chosen at runtime based on system configuration    What does system configuration mean

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As of 8  May  2019   JVM heap size depends on system configuration  meaning   a  client jvm vs server jvm  b  32bit vs 64bit    Links    1  updation from J2SE5 0  https   docs oracle com javase 6 docs technotes guides vm gc-ergonomics html 2  brief answer  https   docs oracle com javase 8 docs technotes guides vm gctuning ergonomics html 3  detailed answer  https   docs oracle com javase 8 docs technotes guides vm gctuning parallel html default heap size 4  client vs server  https   www javacodegeeks com 2011 07 jvm-options-client-vs-server html  Summary    Its tough to understand from the above links  So summarizing them here   1  Default maximum heap size for Client jvm is 256mb  there is an exception  read from links above     2  Default maximum heap size for Server jvm of 32bit is 1gb and of 64 bit is 32gb  again there are exceptions here too  Kindly read that from the links     So default maximum jvm heap size is  256mb or 1gb or 32gb depending on VM  above

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Like you have mentioned  The default -Xmxsize  Maximum HeapSize  depends on your system configuration   Java8 client takes Larger of 1 64th of your physical memory for your Xmssize  Minimum HeapSize  and Smaller of 1 4th of your physical memory for your -Xmxsize  Maximum HeapSize    Which means if you have a physical memory of 8GB RAM  you will have Xmssize as Larger of 8  1 6  and Smaller of -Xmxsizeas 8  1 4    You can Check your default HeapSize with  In Windows   java -XX  PrintFlagsFinal -version   findstr  i  HeapSize PermSize ThreadStackSize    In Linux   java -XX  PrintFlagsFinal -version   grep -iE  HeapSize PermSize ThreadStackSize    These default values can also be overrided to your desired amount

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It varies on implementation and version  but usually it depends on the VM used  e g  client or server  see -client and -server parameters  and on your system memory   Often for client the default value is 1 4th of your physical memory or 1GB  whichever is smaller    Also Java configuration options  command line parameters  can be  outsourced  to environment variables including the -Xmx  which can change the default  meaning specify a new default   Specifically the JAVA TOOL OPTIONS environment variable is checked by all Java tools and used if exists  more details here and here    You can run the following command to see default values   java -XX  PrintFlagsFinal -version   It gives you a loooong list  -Xmx is in MaxHeapSize  -Xms is in InitialHeapSize  Filter your output  e g   grep on linux  or save it in a file so you can search in it

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On my Ubuntu VM  with 1048 MB total RAM  java -XX  PrintFlagsFinal -version   grep HeapSize printed    uintx MaxHeapSize    266338304  which is approx 266MB and is 1 4th of my total RAM

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Surprisingly this question doesn t have a definitive documented answer   Perhaps another data point would provide value to others looking for an answer   On my systems running CentOS  6 8 7 3  and Java 8  build 1 8 0 60-b27  64-Bit Server    default memory is 1 4 of physical memory  not limited by 1GB     Also  -XX  PrintFlagsFinal prints to STDERR so command to determine current default memory presented by others above should be tweaked to the following   java -XX  PrintFlagsFinal 2 gt  amp 1   grep MaxHeapSize   The following is returned on system with 64GB of physical RAM   uintx MaxHeapSize                                     16873684992       product

[java] Default Xmxsize in Java 8 (max heap size)

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