Performance improvements in Cassandra 1.2

Cassandra 1.2 introduces performance optimizations, particularly for clusters with large amounts of data per node. It moves storage engine internal structures off-heap to manage them manually in native memory. Compression metadata and per-row bloom filters are moved off-heap, improving overall performance. Additionally, the update process for indexed columns has been improved, and leveled compaction now supports multiple concurrent compactions across different sstable ranges. The Murmur3Partitioner is introduced as a new default partitioner, offering negligible performance gains over the RandomPartitioner. Streaming optimization allows the kernel to handle data transfers when entire compressed blocks are involved. Hinted handoff in Cassandra 1.2 enables faster recovery of replicas by allowing concurrent delivery of many hints to the target replica.