Cassandra Practice Test

What happens when the memtable content exceeds a threshold in the Write Path?

1. The memtable data is ignored

2. The data is flushed to SSTable on disk

3. New data is appended to the commit log only

4. The system shuts down

The correct answer is: The data is flushed to SSTable on disk

When the content of the memtable exceeds a certain threshold, the system performs a critical operation to ensure data consistency and performance. Specifically, the memtable is flushed to an SSTable (Sorted String Table) on disk. This process is essential for a couple of reasons. First, storing data in memory (as in the memtable) is fast, but memory is a limited resource. To maintain efficient memory usage and prevent potential memory overflow issues, the memtable must be periodically flushed to persistent storage. This not only frees up memory but also ensures durability, as the data is written to disk where it can be retained even in the event of a system failure. Second, this flushing process is tied to Cassandra’s write path architecture, which optimizes for quick write capabilities while still managing data persistence. After the flush operation, the memtable is cleared, and the data can be accessed in the SSTable format, which is optimized for read operations. In summary, the process of flushing the memtable content to an SSTable on disk ensures that Cassandra can maintain its performance for write operations while also protecting data integrity and durability.