Cassandra Practice Test

How does Cassandra improve write performance through its architecture?

1. By ensuring all nodes acknowledge every write

2. By sequentially flushing memtable data to disk only

3. By using append-only writes to commit logs

4. By using synchronous replication across all nodes

The correct answer is: By using append-only writes to commit logs

Cassandra improves write performance primarily through its use of append-only writes to commit logs. This approach means that when data is written to Cassandra, it is added to a commit log in an append-only fashion, which is very efficient for disk I/O operations. Append-only writes minimize the overhead associated with random access writes, significantly speeding up the write process. This architecture allows Cassandra to quickly capture incoming writes without needing to immediately update the in-memory data structures. After data is written to the commit log, it is stored in a memtable (a memory-resident data structure) where it can be accessed quickly. Eventually, the data in the memtable is flushed to disk in a more efficient manner. The use of an append-only mechanism helps to preserve write performance, as it reduces the likelihood of disk seeks. In contrast, ensuring that all nodes acknowledge every write can introduce latency and negatively impact write throughput. Sequentially flushing memtable data to disk is beneficial, but without the efficiency of the commit logs, the initial write pace would be slower. Synchronous replication across all nodes can ensure data consistency but can also introduce additional wait times for write operations, as the system must wait for acknowledgments from multiple nodes. Therefore, the append-only writing method is crucial