Updates to Cassandra’s Commit Log in 2.2

The commit log implementation of Apache Cassandra has been significantly improved in version 2.1, with multithreaded and memory-mapped writing reducing log overheads and improving throughput. In version 2.2, compression was added to the commit log, further enhancing performance by reducing disk transfer and space requirements at the expense of additional CPU processing. The segment reuse feature has been removed in this version to reduce page cache pressure and improve real-world log performance. Compression is configured using the commitlog_compression parameter in cassandra.yaml, with LZ4Compressor recommended for its reasonable compression rates and high throughput. In testing, compression resulted in a 6-12% improvement in write performance and smoother operation under heavy writes.