Get JVM to grow memory demand as needed up to size

Question

We ship a Java application whose memory demand can vary quite a lot depending on the size of the data it is processing. If you don't set the max VM (virtual memory) size, quite often the JVM quits with an GC failure on big data.

What we'd like to see, is the JVM requesting more memory, as GC fails to provide enough, until the total available VM is exhausted. e.g., start with 128Mb, and increase geometrically (or some other step) whenever the GC failed.

The JVM ("Java") command line allows explicit setting of max VM sizes (various -Xm* commands), and you'd think that would be designed to be adequate. We try to do this in a .cmd file that we ship with the application. But if you pick any specific number, you get one of two bad behaviors: 1) if your number is small enough to work on most target systems (e.g., 1Gb), it isn't big enough for big data, or 2) if you make it very large, the JVM refuses to run on those systems whose actual VM is smaller than specified.

How does one set up Java to use the available VM when needed, without knowing that number in advance, and without grabbing it all on startup?

Answer 1

I don't think you can do what you are trying to do; instead you'll have to ship instructions specific to your customers, their systems and their demands of how they can modify your .cmd file to allow for more memory.

Of course, if your product is aimed at very non-technical users, you may wish to hide this behind some more user-friendly config file. E.g.

# HIGH, MEDIUM, LOW - please change as appropriate. The guidelines are:
#                       * HIGH - users who generate 500 items per day
#                       * MEDIUM - 200-500 items etc
memoryUsage=MEDIUM

or possibly deploy different config files depending on which product option a user specifies when they order the product in the first place.

Answer 2

In comments you say that the amount of memory that your application actually depends on the input dataset size provided by the user. This suggests that instead of trying to grab all available virtual memory (which may cause problems for the user's other applications) you should be looking at the input dataset size before you start the JVM and using that to estimate the amount of memory the application will need.

Suppose that the user's machine is configured with modest physical memory and a huge swap space. If you launch the JVM with a huge VM size, it could cause severe "thrashing" as the JVM tries to access data in non-resident pages. By contrast, if you give the JVM something more than the application needs and less than the available physical memory, you should be able to run comfortably without thrashing.

Answer 3

You can also use the option: -XX:+AggressiveHeap

This according to the [documentation][1]:

The -XX:+AggressiveHeap option inspects the machine resources (size of memory and number of processors) and attempts to set various parameters to be optimal for long-running, memory allocation-intensive jobs. It was originally intended for machines with large amounts of memory and a large number of CPUs, but in the J2SE platform, version 1.4.1 and later it has shown itself to be useful even on four processor machines. With this option the throughput collector (-XX:+UseParallelGC) is used along with adaptive sizing (-XX:+UseAdaptiveSizePolicy). The physical memory on the machines must be at least 256MB before AggressiveHeap can be used. The size of the initial heap is calculated based on the size of the physical memory and attempts to make maximal use of the physical memory for the heap (i.e., the algorithms attempt to use heaps nearly as large as the total physical memory).

[1]: http://java.sun.com/docs/hotspot/gc1.4.2/#4.2.2. AggressiveHeap|outline

Answer 4

I do not think either the Sun or IBM JVM can do this (I know that the AS/400 one can, but that is most likely not relevant to you).

I would suggest using Java WebStart (and before you discard this, then notice that it has been updated with Java 6 u 10 and is much better suited for launching "local" applications and applet) since it allows you to provide a "small instance", "larger instance", "gigantic instance" as links/icons.

You will most likely look into the "inject application in webstart cache" and "offline"options.

Answer 5

There is two options in the virtual machine arguments that can be used : -Xms to set the memory size at startup and -Xmx to set the maximum memory size...

You can set a low startup memory and a big maximum one, so the VM will allocate new memory only if needed.

Answer 6

I read through the threads but didn't see anything which indicated that the application had undergone some sort of profiling. Normally I'd profile the apps under certain conditions to find hot spots in performance or memory usage. There's probably things that could be improved in most cases.

If you could establish the limits and understand the behavior of the application you could be in a position to better tell your customers what they can or cannot do with the application thereby reducing the amount of support calls and giving you a better idea of what minimum or maximum heap size to ship the product with.

Maybe you could start with this: http://www.eclipse.org/mat/