Question

We have a collection of objects which grows quite large over time. We have implemented a caching strategy to help alleviate this, however we are still running out of Heap Space at run time – if enough memory isn’t allocated at startup.

Is there a standard mechanism to reduce the size of this cache at runtime to remove these OutOFMemory errors? This way if our process is started with a smaller slice of memory than normal we can hopefully avoid the server dying.

I realize that this is an Error type and thus shouldn’t be caught / processed as it’s normally indicative of more serious issue.

Is it as simple as having something as follows:

private static final long RECOMMENDED_MEMORY = 1073741824L;  //Example 1 Gig
private static int recommendedCacheSize = 100; //Example of 100 items
long heapSize = Runtime.getRuntime().totalMemory();
double size = Math.floor((double) heapSize/RECOMMENDED_MEMORY * recommendedCacheSize);
recommendedCacheSize = ++size; 

Answer 1

Why not use something that was designed as a real cache?

While you could use soft references to implement a memory-sensitive cache, such caches tend to leave objects in memory too long (increasing your GC load). Weak references are not suitable for caches, as they have a much higher likelihood of being cleared (in practice, they’re cleared on every GC).