What role does the Commit Log play in the Cassandra write path?

The Commit Log serves a crucial role in the Cassandra write path by logging every write operation before it is applied to the data storage system. This logging mechanism is essential for data durability and recovery. When a write operation is executed, the data is first recorded in the Commit Log, ensuring that even if the system crashes immediately after a write, the data can still be recovered by replaying the entries from the Commit Log.

This feature helps maintain the consistency of data by guaranteeing that no writes are lost during failures. Once the write is confirmed in the Commit Log, it can proceed to the Memtable, where it resides in memory until it is eventually flushed to disk in an SSTable format for more permanent storage.

Other options present alternatives that do not accurately describe the Commit Log's purpose. For example, the Commit Log is not a temporary store for read queries, does not serve as a permanent data store, nor is it involved in handling user authentication. Its primary responsibility lies in ensuring that all write operations are recorded for reliability and data integrity in a distributed environment like Cassandra.