Off-heap memtables in Cassandra 2.1

The text discusses the importance of moving data structures off the Java heap to native memory due to increasing dataset sizes and limitations on JVM heap size. In Cassandra 2.1, improvements are made to reduce the footprint of memtables with a new configuration option called `memtable_allocation_type`. Two options are provided: `heap_buffers` (default) and `offheap_objects`, which is expected to become the default in version 3.0. Laboratory tests show that enabling `offheap_objects` results in approximately 5% faster writes due to less frequent flushing, leading to larger SSTables and reduced compaction needs. Reads remain unchanged but may vary under different workloads. Future enhancements are planned to better test the performance of memtables with more demanding scenarios.