SSTable is an abbreviation of the term “Sorted String Table” and is the technique used by Cassandra to store data on disk. The fundamental concept of an SSTable was first implemented in Google’s BigTable. In simple terms, an SSTable is a commit log that only allows appending data. SSTables are highly efficient for write operations and can also be compacted for storage optimization. Cassandra uses in-memory tables also known as “memtables” to buffer writes and sorting of data before actually commiting changes to the SSTable.