AEM Memory Issues and How to Fix

Symptoms of a memory issue

• AEM crashes randomly and in the logs OutOfMemoryError is observed
• AEM gets slower over time and eventually crashes
• AEM is unresponsive

Diagnosing a memory issue

• Search the log files for OutOfMemoryError, if you find any matches then you have a memory issue
• Review the http://aem-host:port/system/console/memoryusage screen
  If the "Old Generation" (JDK 7 and earlier) or "Tenured Generation" (JDK8 or later) usage is high then this could be a sign of a heap memory utilization issue.  Click "Run Garbage Collector" to request the JVM to run a full heap garbage collection.  If the high heap utilization stays high after requesting GC then there is likely an issue.  On an AEM instance with Oak Tar storage, if the tenured usage is higher than 3GB then there might be a problem.  High heap utilization on a system with Mongo storage could be due to the in-memory cache configuration.
• Take thread dumps and top output and perform thread analysis.  Check if the threads causing high CPU utilization are native JVM Garbage Collection threads.  If the thread using the most CPU time are the "VM Thread" or any garbage collection threads then there is likely a memory issue.

What causes memory issues

• Java application memory leak
• Java Finalizer pile up due to incorrect use of finalize in custom code
• Insufficient max heap configuration

How to analyze the cause of your memory issue

See this article for details on how to capture a heap dump.

The best way to identify the cause of a memory issue is to analyze a heap dump.  

Once you've captured a Heap Dump file then open it in Eclipse MAT or IBM Memory Analyzer tool.  In Eclipse MAT, run the Leak Suspects report and open "Thread Details" view to see potential causes for the memory issue.

Solutions to common memory issues

• Optimize your application code to utilize less memory if you notice long garbage collection pauses.  Most Garbage Collection issues can best be solved by optimizing the application versus tuning the JVM.
• If you have already optimized your application and still experience long GC pauses then focus on tuning the JVM.