OutOfMemoryError in Ubuntu server

Question

I have a server, written in java that working fine in Windows 7. But when I installed the same in Ubuntu, it shows out of memory error, server having 8 GB of ram and our server using only 70% of Ram, it shows out of memory error. And CPU usage is at the peak at out of memory time.

1. How can I allocate the remaining 30 % of ram to my application?
2. How can I increase the limit of memory that allocated to an application in Ubuntu?

Out of memory error does not occur in Windows, only Ubuntu. In the windows Task manager shows 100% CPU usage and full RAM usage. I wish to implement this performance in Ubuntu.

Answer 1

If you mean that Java throws an OutOfMemoryError, you first need to understand why. You probably want to pick up a profiler like VisualVM (free) or YourKit (not free) to see what's going on in memory. After that, you can decide on the appropriate action(s), like making your app more memory-efficient or changing the JVM settings to increase the appropriate memory allocation.

To get you started, if you're running out of heap space (old generation), you can adjust the maximum heap available using the JVM flag -Xmx. For example, -Xmx1024m or -Xmx1g will set the max to 1GB. If it's the permanent generation (PermGen), you can allocate a larger chunk of overall heap to that using the -XX:MaxPermSize JVM flag, such as -XX:MaxPermSize=256m. Note that increasing the size of the permanent generation will correspondingly decrease the amount of memory available to the other heap segments.

Full details on these and other JVM memory settings can be found on the Java application launcher page and the HotSpot VM Options page (assuming you're using the HotSpot VM).

Answer 2

You can use ulimit to restrict the RAM usage for desired processes.

Additionally, for Java applications, you can pass arguments like -Xms (minimum), -Xmx (maximum) to java process (M for MBs, G for GBs).