I'm experiencing OutOfMemoryErorrs when performing a simple CREATE INDEX command on tables with more than 500,000 rows.
The crashes occured not deterministically in our standard environment using 64MByte heap space. But you can easily reproduce the error using the the repro database attached, when running it with 12MByte heap space.
Just start ij with the -Xmx12M JVM argument, connect to the sample db and execute
CREATE INDEX IDX_CUSTOMER_NAME ON CUSTOMER (NAME).
I've done some investigation and i was able to track down the error. It occurs in SortBuffer.insert(), but not as expected in NodeAllocator.newNode() (there is a handler for the OOE), but already in the call of sortObserver.insertDuplicateKey() or .insertNonDuplicateKey() (where the data value descriptors are cloned).
Unfortunately this is not the point to fix it. As i caused the MergeRun (that spills the buffer to disk) to happen earlier, it did not significantly lower the memory consumption. Instead it created about 13,000 temp files with only 1KByte size (because of the many files, performance was inacceptable).
So i analyzed the heap (using the HeapDumpOnOutOfMemory option) and saw that it's not the sortbuffer that consumes most of the memory (just few KBytes and about 6% of the memory), but the ConcurrentCache. Even though the maxSize of the ConcurrentCache was set 1000, the cache contained about 2,500 elements. I've also attached the heapdump.
If i'm understanding the concept right, the cache elements are added without regarding the maxSize and there's a worker thread that runs on low prio, that shrinks the cache from time to time to 10% of its size.
I think in this particular case, where memory is getting low, it would be a better idea to have the cache cleared synchronously and provide more space to the sortBuffer. Maybe that could be done in the ClockPolicy.insertEntry() in case, that the current size is increasing the max size by 50%. I'm not already very familiar with the code, so i failed to do so.
I hope you got all the information you need, if you require any further information, please let me know.