Java OutOfMemoryError

Memory Leak Symptoms

  • Performance: Usually associated with excessive object creation and deletion, long delays in garbage collection, excessive operating system page swapping, and more. Works find with small data sets.
  • Resource constraints: occurs when there’s either to little memory available or your memory is too fragmented to allocate a large object - this can be native or, more commonly, Java heap-related.
  • Java heap leaks: the classic memory leak, in which Java objects are continuously created without being released. This is usually caused by latent object references.
  • Native memory leaks:associated with any continuously growing memory utilization that is outside the Java heap, such as allocations made by JNI code, drivers, or even JVM allocations.
  • Spontaneous crashes

Not all OutOfMemoryError(OOM) imply memory leaks: an OOM can occur due to the generation of a large number of local variables or other such events. On the other hand, not all memeory leaks necessarily manifest themselves as OOMs, especially in the case of desktop applications or client applications (which aren’t run for very long without restarts)

OutOfMemoryError error messages

  • java.lang.OutOfMemoryError: Java heap space
  • java.lang.OutOfMemoryError: PermGen space
  • java.lang.OutOfMemoryError: Requested array size exceeds VM limit
  • java.lang.OutOfMemoryError: Request <size> bytes for reason <reason>. Out of swap space?
  • java.lang.OutOfMemoryError: <reason> <stack trace> (Native method)

Application Crash Without OOM

  • Running native code that doesn’t check for errors returned by memory allocation functions
  • Fatal error log or crash dump
    • The system might be configured with insufficient swap space
    • A process might be consuming all available memory resources (My issue)

Common Memory Leaks

  • File/Text buffers not closed
  • Hash maps keeping references alive (static variables)
  • Hashmap Key equals() and hashcode() are not implemented (Keep growing even the object has same values because hashmap is using the reference of the object)
  • Inner classes that reference outer classes can leak. (make them static to avoid)

Diagnosing and fixing Leaks

  • Identify symptoms
    • Check the system configuration. If it is gone after increasing memory, it maybe not a leak issue. Since it requests more memory than the runtime heap offers, it can be due to poor design. For instances, creating multiple copies of an object or loading a big dataset into an array.
    • If an application steadily increases its memory utilization while processing the same kind of data, it might have a memory leak.
  • Enable Verbose Garbage Collection
    • The -verbosegc argument allows you to generates a trace each time the garbage collection (GC) process is begun. The summary reports are printed to standard error, giveing you a sense of how the memory is being managed.
  • Enable Profiling (VirtualVM tool)
    • jstatd
    • JMX (Java Management Extensions)
      VisualVM will automatically detect and connect to JVM applications that are running on version 6 of the JDK or that that have been started with the correct system properties on Version 5.0.
# tools.policy
grant {

jstatd -p 1089
java \ \ \
  • Analyze the Trace


Written on March 18, 2022