Why does top report that Cassandra is using a lot more memory than the Java heap max?
Cassandra uses mmap to do zero-copy reads. That is, we use the operating system’s virtual memory system to map the sstable data files into the Cassandra process’ address space. This will “use” virtual memory; i.e. address space, and will be reported by tools like top accordingly, but on 64 bit systems virtual address space is effectively unlimited so you should not worry about that.
