Cassandra Practice Test 2025 – Comprehensive All-in-One Guide to Exam Success!

The primary purpose of the commit log in Cassandra is to replay data if a crashed node restarts. The commit log serves as a write-ahead log that captures all write operations before they are applied to the in-memory data structures and eventually persisted to disk. This mechanism ensures data durability, as it allows the system to recover data that might otherwise be lost due to a failure or crash. Upon recovery, Cassandra uses the information stored in the commit log to reconstruct the state of the database and apply any missed write operations that were not yet flushed to the SSTables on disk.

While the commit log indirectly aids performance and contributes to memory management, its core function is primarily focused on maintaining a reliable recovery mechanism, making it essential for fault tolerance and data integrity in distributed systems like Cassandra. Thus, when a node restarts after a crash, the commit log is instrumental in restoring the data to its most recent state by replaying the logged write operations.