I’m curious how the JVM efficiently allocates many small objects. How does it avoid memory fragmentation? Or does it request a large block of memory from the OS at the start? (last q is probably easily googled)
There is intermediate fragmentation due to dead-but-not-yet-collected objects. Together with the use of different generational regions, GC languages thus require more memory (a rule of thumb is twice the memory of a non-GC program), but memory is cheap, and not having to reference-count and deallocate each object individually can conversely have performance benefits.
Do you know if the early generation region settings can be tweaked (alignment, size, number of threads/regions)? I’m wondering what happens if you “overflow” these areas by generating too many objects
One situation you can run into is if you generate and quickly drop objects faster than the GC can collect them, or rather, the process spends most of its time with GC rather than with actual program execution, then after a certain while an exception will be raised. That situation almost always indicates a bug in your program, and the exception helps to see the cause of the program stalling. Of course that behavior is also configurable.