January 2014 Summaries

Compaction is a process in Cassandra whereby log-structured data files are merged to evict obsolete or deleted rows. The first component consulted on a read is the Bloom filter, which is a probabilistic set that saves memory by taking just a few bits per key stored. However, bloom filters are not re-sizeable and can waste space if sstables overlap. To solve this problem, Cassandra 2.1 uses HyperLogLog for cardinality estimation to get an accurate count of how much the compacting sstables overlap, saving about 40% of the bloom filter overhead. Experimentally, using cardinality estimation to pick better compaction candidates could be a significant improvement for overwrite-heavy and append-mostly workloads.

The C# driver enables .Net developers to create applications using Cassandra, exclusively working with CQL3. It separates functionality into lower-level API calls and a LINQ2CQL layer. To get started, add the NuGet package reference to your project. Connecting to a Cassandra cluster involves creating a Cluster object and calling its Connect() method. The returned Session object is used for all operations against the cluster. Data can be queried or inserted using inline CQL statements, prepared statements, or batch jobs. The LINQ2CQL driver, found in the Cassandra.Data.Linq namespace, provides extensive capabilities for working with data and requires a dedicated blog post to fully describe its features.