GC（分配失败）VS OutOfMemoryError 异常

Question

'OutOfMemoryError': Usually, this error is thrown when there is insufficient space to allocate an object in the Java heap.

GC (Allocation Failure): Allocation Failure” means that there is an allocation request that is bigger than the available space in young generation.

Does this mean Allocation Failure will be thrown when Young generation memory is full (Minor GC) and "OutOfMemoryError" is thrown in full GC?

Answer 1

These could become related as far as I can tell; but they are entirely different things.

OutOfMemory is an error you can not recover from - the JVM will die at this point.

GC (Allocation Failure): Allocation Failure is the reason why GC will kick in (and do a minor collection). At this point some things might happen, like: enough space is freed for the new allocation to fit into young generation . Or that did not happen and some objects will be promoted to the old generation . If they can't be promoted , a full GC might be triggered - and if that does not free enough space an OutOfMemory might be thrown.

Answer 2

In general, an OutOfMemoryError occurs when you have exceeded the maximum memory you have already allocated to the JVM. This amount can be changed when starting java using jvm parameters. eg -Xmx2G . Note that this amount isn't used immediately. See below.

GC (Allocation Failure) is similar, except it occurs when the garbage collector runs out of memory on the heap, and it attempts to allocate more. If your allocated memory is higher than your available system memory, this will fail. Essentially, the JVM tries to allocate memory which isn't there.

See for more information

Answer 3

Allocation (Evacuation) Failure

As with CMS, the G1 collector runs parts of its collection while the application continues to run and there is a risk that the application will allocate objects faster than the garbage collector can recover free space. See the section Concurrent Mode Failure in Concurrent Mark Sweep (CMS) Collector for the analogous CMS behavior. In G1, the failure (exhaustion of the Java heap) occurs while G1 is copying live data out of one region (evacuating) into another region. The copying is done to compact the live data. If a free (empty) region cannot be found during the evacuation of a region being garbage collected, then an allocation failure occurs (because there is no space to allocate the live objects from the region being evacuated) and a stop-the-world (STW) full collection is done.