Caching in Cassandra 1.1

Cassandra has built-in key and row caches since versions 0.5 and 0.6, respectively. Key cache saves primary key indexes for a table, while the row cache is similar to memcached, pulling entire rows into memory for faster access. Typically, one of these caches is enabled per table, with exceptions for infrequently read archive tables. Cache sizes do not need to be specified per table and are managed automatically based on size and access frequency. The main settings are key_cache_size_in_mb and row_cache_size_in_mb in cassandra.yaml. Row cache hit rate should ideally be at least 90%. Limitations include the inability to cache compound-key rows, which is being addressed in Cassandra 1.2.