What is xmx and xms?

xmx?and?xms?are JVM,?Java Virtual Machine, command-line options/flags that are used by programmers to manipulate the heap size used by JVM. This allows them to optimize the speed and memory of different java applications.

About?xms

• xms?is used to specify the initial?lower bound?of java heap memory size.
• Default?xms?size is 1/64th of the physical memory size.
• Format for specifying?xms:

java?-xms{Numerical?Size}{Unit}        

where?Unit?is?k/K

k/K?for kilobytes,?m/M

m/M?for megabytes, and g/G for gigabytets.

• The numerical size must be a?whole number.
• By default, the size is in bytes.

About?xmx

• xmx?is used to specify the?upper bound?of java heap memory size.
• Default?xms?size is 1/4th of the physical memory size.
• Format for specifying?xms:

java?-xms{Numerical?Size}{Unit}        

where Unit is k/K for kilobytes, m/M for megabytes, and g/G for gigabytes.

• The numerical size must be a?whole number.
• By default, the size is in bytes.

Pitfalls

• If the programmer initializes a fairly large heap size, then the?Garbage Collector?will consume more time while clearing the memory, which will slow down the program.
• If the programmer initializes a fairly small heap size, then it is possible to run out of memory. Insufficient memory will throw the following exception:?java.lang.OutOfMemoryError: Java heap space.