We found following advices about setting JVM (Java Virual Machine) options -Xms and -Xmx.

So, why set -Xms and -Xmx as the same value?

Firstly, we need to know what are -Xms and -Xmx.

-Xms and -Xmx

The -Xms option sets the initial and minimum Java heap size. This -Xmx option sets the maximum Java heap size.

Java Heap : The Java heap ( the "Heap") is the part of the memory where blocks of memory are allocated to objects and freed during garbage collection.

Advantages of same value

1. Predictable Performance:

   • Ensures that the JVM always has the same amount of memory available from the start.

   • Avoids potential performance hiccups caused by memory risizing.

   • Beneficial for applications with consistent memory requirements.

     ::: banner {tip} In a production environment, if you monitor the GC data, you will notice that is a relatively short period of time (usually less than an hour), the JVM will eventually increase the heap size to the -Xmx setting. Each time the JVM increases the heap size it must ask the OS for additional memory, which takes time (and thus adds to the response time of any requests that were is process when the GC hit). And usually the JVM will never let go of that memeory. Therefore, since the JVM will eventually grab the -Xmx memory, you might as well set it to that at the beginning.

From peterj's anwser to question Why to set -Xms and -Xmx to the same value? :::

2. Reduced Garbage Collection Overhead:

   • GCs will happen not as often.

   • Minimizes garbage collection pauses, leading to smoother application performance.

3. Enhanced Stability:

   • Minimizes the risk of out-of-memory errors (OOM) due to unexpected memory usage spikes.
   • Prevents potential crashes or instability caused by insuffient memory.

4. Easier Troubleshooting:

   • Simplifies memory-related debugging as you know the exact heap size being used.

When to consider setting -Xms and -Xmx to the same value

• In a production environment running only one app server per OS (or per VM).

  So since the app server is not competing for memory with other apps you might as well give it the memory up front.

  Note
  

  It applies also to the syatem test environment since the system test environment should mimic production as close as possible.

  For development, make -Xms and -Xmx different. Usually, you are not doing much work with the app server in development, so it will often stay with the -Xms heap setting. Also, since in development the app server will share the machine with lots of other apps (mail client, word processors, IDEs, databases, browsers, etc), setting the -Xms to a smaller size lets the app server play more nicely with the other software that is also competing for the same resources.

  From peterj's anwser to question Why to set -Xms and -Xmx to the same value?

• Applications with stable memory Footprint: Such as web servers or long-running batch jobs.

• Latency-sensitive application: Where even minor garbage collection pauses can negatively impact user experience.

• Mission-critical applications: That require high availability and connot afford unexpected crashes.

Important considerations

• Ensure Available Memory: Allocate enough memory to accommodate your application's needs without starving other processes or the operating system.
• Monitor Memory Usage: Track memory consumption to fine-tune these settings if needed.
• Adjust for Specific Requirements: Consider individual application characteristics and performance goals when deciding on memory allocation.
• Considering Different Virtual Machine: There are many kinds of GC strategies for the same JDK and cannot be generalized. In addition, for the Hotspot virtual machine, Xms and Xmx are set to the same, which can reduce the pressure caused by the scaling heap size. But for IBM virtual machines, setting it to the same value will increase the probability of heap fragmentation, and this negative impact is enough to offset the benefits of the former.

See also

• Why to set -Xms and -Xmx to the same value?