Question

When a record isn't available in the row cache,

a) Cassandra retrieves it from the Memtable;
b) Cassandra fetches it from the Commit Log;
c) Cassandra performs a disk I/O operation;
d) Cassandra generates a new record.

Answer 1

Cassandra retrieves a missing record by first checking the Memtable, and if not found there, it performs a disk I/O operation to retrieve data from the SSTable.

Step-by-step explanation:

When a record is not found in Cassandra's row cache, the system does not immediately retrieve it from the commit log. Instead, the correct sequence of actions would see Cassandra attempting to find the record in the Memtable. If the record is not in the Memtable, then Cassandra proceeds to perform a disk I/O operation. During this operation, Cassandra consults the SSTable on disk to locate the requested data. It is essential to note that the commit log's main purpose is to ensure data durability, serving as a write-ahead log for recovery in case of a crash and not for reading data in response to client queries.