When Java Memory Issues aren't.

What I'm going to write is likely an unpopular viewpoint, but one that needs to be expressed. One of the most frequent sentiments expressed by customers when we are doing an application analysis is that their Java application is suffering from crippling memory issues. I'm not going to go on record saying that memory issues don't happen in Java -- I'm quite certain that there are situations where legitimate memory management issues within applications and the virtual machine happen. But, a more common scenario is something like customers placing very large objects into user http sessions, then being surprised when their application server slows to a crawl and crashes out of memory. Guess what? That's not a memory issue, that's a poor architecture and design issue.

Normally about this time I hear a chorus of "but, but, but! Why isn't the VM managing my memory correctly?!?!?!" It's a virtual machine, not a miracle worker. In the case above, the http session is being abused and overused. There are several options to that particular problem, depending on the business requirements:

a) Reexamine necessity of all data being stored in the session and reduce.
b) Move much of the data to a separate cache with more granular control over cache clear/timeout strategy.
c) Externalize session data entirely to a separate user session server with purpose-built hardware and cache timeout strategy.

All of the above are overkill you say? Sure beats running out of memory it seems to me. About this time I often hear someone pipe up about "Why don't we just force garbage collection?" or some similar pearl of wisdom, such as explicitly finalizing objects. Both are flawed -- you'll recall that the vm specification states that marking an object to be finalized does not explicitly force it to be finalized on any particular schedule, and any suggestion of forced garbage collection is specifically not recommended. Generally the response I hear to this is some grumbling about a lack of control over memory management. Therein lines the rub: If you need explicit memory management due to the nature of your requirements, then Java and .Net are not for you. And, as demonstrated above many issues that at first appears to be memory related are in fact not.