7 JVM Heap Size Best Practices

The Java Virtual Machine (JVM) heap size is the amount of memory the JVM will use to store objects created by your application. If your heap size is too small, your application will run out of memory and crash. If your heap size is too large, your application will use more memory than it needs and could run slowly.

You can set the JVM heap size when you start your application. The exact syntax for doing this varies depending on the application server you are using, but the general format is to use the -Xmx and -Xms parameters to set the minimum and maximum heap size, respectively.

For example, to set the heap size to 512 MB, you would use the following parameters:

-Xmx512m -Xms512m

The Xmx parameter sets the maximum heap size and the Xms parameter sets the minimum heap size.

1. Set the initial and maximum heap size to the same value

When the initial and maximum heap size are not set to the same value, the JVM will resize the heap during runtime which can cause performance issues. If the JVM has to resize the heap too often, it can impact application performance.

It’s also important to make sure that the heap size is not set too large. If the heap size is too large, it can cause GC pauses and affect application performance.

2. Use a 64-bit JVM on a 64-bit OS

A 64-bit JVM can address more memory than a 32-bit JVM, so it can take advantage of any extra RAM you have in your system. If you’re using a 32-bit JVM on a 64-bit OS, you’re not getting the full benefits of a 64-bit system.

Additionally, a 64-bit JVM can use larger heaps more efficiently than a 32-bit JVM. This is because a 64-bit JVM can pack objects closer together in memory, leading to better memory utilization and less wasted space.

Finally, a 64-bit JVM can perform some operations more efficiently than a 32-bit JVM. For example, 64-bit CPUs often have native support for 64-bit integer arithmetic, which can lead to faster performance for certain types of calculations.

3. Use G1 GC for large heaps

G1 GC is a low-latency garbage collector that can help reduce GC pauses. It’s especially well suited for large heaps, which can often cause long GC pauses with other collectors.

If you’re using a large heap, G1 GC is definitely worth considering. It can help keep GC pauses to a minimum, which can be a big benefit for applications that need to be highly responsive.

4. Monitor your garbage collection (GC) logs

GC logs provide a wealth of information about what’s going on inside the JVM. By monitoring GC logs, you can detect issues such as memory leaks and optimize your heap size accordingly.

There are many tools available for monitoring GC logs, but one of the most popular is GCViewer. GCViewer is open source and can be used to visualize GC logs in a variety of formats, including CSV, XML, and JSON.

Once you have GC logs, you can use them to determine the optimal heap size for your application. To do this, look for long GC pauses and high CPU utilization. If you see either of these, it’s likely that your heap size is too small and you need to increase it.

5. Tune your JVM flags

JVM flags are settings that control the behavior of the Java Virtual Machine. By default, the JVM uses a set of flags that work well for most applications. However, in some cases, you may need to tune these flags to get the best performance for your application.

For example, if you’re using a lot of memory, you may need to increase the size of the heap. Or, if you’re seeing a lot of garbage collection activity, you may need to adjust the garbage collector’s settings.

Tuning your JVM flags can be a complex process, and it’s important to understand the impact of each flag before making changes. However, if you take the time to tune your flags, you can see significant improvements in performance.

6. Check your application’s performance regularly

If your application is not performing well, it’s likely that your JVM heap size is too small. By checking your performance regularly, you can ensure that your JVM heap size is always optimal.

There are a few different ways to check your performance. One way is to use a tool like JConsole or VisualVM. These tools will allow you to monitor your application’s memory usage and garbage collection activity.

You can also use a tool like GCeasy to analyze your application’s GC logs. This will give you insight into how your application is using memory and where any potential issues are.

Finally, you can use a tool like jHiccup to measure your application’s response time under load. This is useful for identifying any bottlenecks in your application.

By checking your application’s performance regularly, you can avoid potential issues and keep your JVM heap size optimized.

7. Consider using an APM tool

When your application is running in production, it is important to have visibility into how it is performing. This includes understanding what your JVM heap size is and whether or not it needs to be adjusted.

An APM tool can provide you with this visibility by monitoring your JVM heap size and providing you with alerts if it gets too low or starts growing too large. This way, you can make the necessary adjustments to keep your application running smoothly.

There are many different APM tools available, so be sure to do your research to find one that best fits your needs.