Detecting out of memory errors

Question

I would like to provide my system with a way of detecting whether out of memory exception has occurred or not. The aim for this exercise is to expose this flag through JMX and act correspondingly (e.g. by configuring a relevant alert on the monitoring system), as otherwise these errors sit unnoticed for days.

Naive approach for this would be to set an uncaught exception handler for every thread and check whether the raised exception is instance of OutOfMemoryError and set a relevant flag. However, this approach isn't realistic for the following reasons:

• The exception can occur anywhere, including 3rd party libraries. There is nothing I can do to prevent them catching Throwable and keeping it for themselves.
• Libraries can spawn their own threads and I have no way of enforcing uncaught exception handlers for these threads.

One of possible scenarios I see is bytecode manipulation (e.g. attaching some sort of aspect on top of OutOfMemoryError), however I am not sure if that's right approach or whether this is doable in general.

We have -XX:+HeapDumpOnOutOfMemoryError enabled, but I don't see this as a solution for this problem as it was designed for something else - and it provides no Java callback when this happens.

Has anyone done this? How would you solve it or suggest solving it? Any ideas are welcome.

Answer 1

You could use an out of memory warning system; this http://www.javaspecialists.eu/archive/Issue092.html can be an inspiration. You could configure a listener which is invoked after a certain memory threshold ( say 80%) is breached - you can use this invocation to start taking corrective measures.

We use something similar, where we suspend the component's service when the memory threshold of the component reaches 80% and start the clean up action; the component comes back only when the used memory comes below a another configurable value threshold.

Answer 2

There is an article based on the post that Scorpion has already given a link to.

The technique is again based on using MemoryPoolMXBean and subscribing to the "memory threshold exceeded" event, but it's slightly different from what was described in original post.

Author states that when you subscribe for the plain "memory threshold exceeded" event, there is a possibility of "false alarm". Imagine a situation when the memory consumption is above the threshold, but there will be a garbage collection performed soon and a lot of the memory is freed after that. In fact that situation is quite common in real world applications.

Fortunately, there is another threshold, "collection usage threshold", and a corresponding event, which is fired based on memory consumption right after garbage collection. When you receive that event, you can be much more confident you're running out of memory.