Cassandra Practice Test

What characteristic defines a Memtable in Cassandra?

1. Immutable data structure

2. Ordered by partition key and clustering columns

3. Stored permanently in disk

4. Shared among multiple tables

The correct answer is: Ordered by partition key and clustering columns

A Memtable in Cassandra is defined as an in-memory data structure that holds writes before they are flushed to disk. One of the key characteristics of a Memtable is that it is ordered by partition key and clustering columns. This ordering is beneficial because it maintains a structured organization of the data, which facilitates efficient reads and writes. When data is written to Cassandra, it first goes to the Memtable, where it is stored in a sorted manner. This enables quick access and modifications before the data is eventually written to SSTables on disk. The ordering by partition key and clustering columns allows for efficient range queries and retrieval based on the organization of the data, maximizing performance. In contrast, the other options do not accurately describe Memtables. While Memtables are indeed written to disk later on, they are not stored permanently in the long term in this form (as option C suggests). They are also mutable during their lifespan, which counters the notion of immutability (as in option A). Finally, Memtables are not shared among multiple tables; each table in Cassandra has its own Memtable that is unique to its dataset, ruling out option D.