Memtables store the current mutations applied to Column families. They function as a write back cache and provide faster write performance and faster read performance for recently written data. Mutations are organized in sorted order using skip list data structure in the Memtable. Each Column family is associated with its own Memtable. In this blog, on-heap based Memtable type is described. | Key Concepts
SSTable is an abbreviation for Sorted String Table. It is the fundamental storage building block in few of the modern Log Structured Merge Tree(LSM) based distributed database systems and key-value stores. It is used in Cassandra, BigTable and other systems. SSTable stands for Sorted Strings Table which stores a set of immutable row fragments or partitions in sorted order | Key Concepts