Since the default memory setting usually is around 64 or 128MB (256MB in Confluence 2.2 and later), you might have to adjust the settings to run a bigger Confluence instance with sufficient memory.

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Diagnosis and Common Causes

There are several reasons that out of memory exceptions can be thrown. Either the virtual machine Confluence is using has hit its allocated memory limit, the system on which Confluence is running has run out of physical and virtual memory, or Confluence is consuming too much memory. In the first case, you should modify the maximum heap size of the virtual machine, per the instructions in this document; in the second or third cases, the solution is to identify the culprit of the memory leak.

For help determining which memory settings to choose, consult Managing Application Server Memory Settings.

If you have not yet set your memory settings and your usage has increased, it's likely that you must set your memory, described below. If your usage patterns have not changed but you've added a plugin or done an upgrade, it's likely that there is a memory leak in a plugin.

1. If you're using the in-memory database (HSQLDB), migrate to an external database. The in-memory database can use a lot of memory.
2. If you are using XML backups, disable them and move to the Alternative Backup Strategy. The XML backup process can be a memory hog.

To troubleshoot potential memory leaks, enter Plugin Support Mode. Take thread dumps during normal operations and during an outage, and submit this information in a support ticket.

Determining Heap Errors Versus Permanent Generation Size (PermGen) Errors

Heap space memory errors will contain only a java.lang.OutOfMemoryError. If you get the error message: java.lang.OutOfMemoryError: PermGen space this means that you have exceeded Java's fixed 64Mb block for loading class files. You will need to add the argument -XX:MaxPermSize=256m to JAVA_OPTS, in addition to any argument you use to set the heap size.

PermGen Space Parameters

Heap Space Parameters

Setting the Memory Settings

How to set the heap or permanent generation memory depends on your distribution, platform, and how you start Confluence. Refer to Configuring System Properties.

Other OutOfMemoryErrors

OutOfMemoryError: unable to create new native thread

This error occurs when the operating system is unable to create new threads. This is due to the JVM Heap taking up the available RAM.

Big heaps take away from the space that can be allocated for the stack of a new thread

For Linux the maximum heap size of the JVM cannot be greater than 2GB. If you only have 2GB RAM in your server, it is not recommended to set the Max size of the JVM that high.
The size of the stack per thread can also contribute to this problem. The stack size can reduce the number of threads that can be created.

To fix this problem, you should reduce the size of your JVM Heap and also the size of the stack per thread.
The stack size can be changed with the following (example) parameter:

"-Xss512k"

Please refer to this guide as a reference for JVM tuning.

OutOfMemoryError: GC overhead limit exceeded

This error indicates that the JVM took too long to free up memory during its GC process. This error can be thrown from the Parallel or Concurrent collectors.

The parallel collector will throw an OutOfMemoryError if too much time is being spent in garbage collection: if more than 98% of the total time is spent in garbage collection and less than 2% of the heap is recovered, an OutOfMemoryError will be thrown. This feature is designed to prevent applications from running for an extended period of time while making little or no progress because the heap is too small. If necessary, this feature can be disabled by adding the option -XX:-UseGCOverheadLimit to the command line.

This kind of OutOfMemoryError can be caused if your java process is starting to use swapped memory for its heap. This will cause the JVM to take a lot longer than normal to perform normal GC operations. This can eventually cause a timeout to occur and cause this error.

To overcome this issue, you need to make sure that all processes can't allocate more memory than there is system memory. In practice this is impossible to do for all processes. At a minimum you should make sure that all your jvm's do not have a total maximum memory allocation than your normally available system memory.

Please refer to this guide for more information.

OutOfMemoryError: Requested array size exceeds VM limit

This error indicates that Confluence attempted to allocate an array that is larger than the Java heap size. More details regarding this error can be found here.
This is due to a known limitation of the JVM as documented here. We have a bug lodged against this, to better handle this exception in Confluence.

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