CASSANDRA Skills 4

Question 1

A developer wants to add a new column to an existing Cassandra table without downtime. Which CQL statement should they use?

Accepted Answer

ALTER TABLE orders ADD shipped_date timestamp

Answer

ALTER TABLE ... ADD is the correct CQL syntax for adding a new column to an existing table, and it is a schema-only change with no data rewrite.

Question 2

What is a Cassandra lightweight transaction (LWT) and when would you use it?

Accepted Answer

A compare-and-set operation that uses Paxos to guarantee conditional writes

Answer

LWTs use the Paxos consensus protocol to implement conditional INSERT/UPDATE/DELETE operations (e.g., INSERT IF NOT EXISTS), at the cost of higher latency.

Question 3

How does the virtual node (vnode) feature improve cluster operations compared to single-token assignment?

Accepted Answer

Vnodes make data distribution more even and simplify adding or removing nodes

Answer

With vnodes, each physical node owns many small token ranges, so bootstrapping and decommissioning redistributes data in smaller, parallel streams.

Question 4

Which read consistency level provides the lowest latency but weakest consistency guarantee in Cassandra?

Accepted Answer

ONE

Answer

Consistency level ONE returns the response from the first replica that responds, offering the fastest reads but risking stale data.

Question 5

What is the effect of setting a very low `memtable_flush_writers` value in a write-heavy Cassandra workload?

Accepted Answer

Memtable flushes will become a bottleneck, increasing write latency

Answer

Too few flush writers means memtables queue up waiting to be flushed to disk, which eventually backs up the write path and increases latency.

CASSANDRA - Apache Cassandra Database Practice Test

CASSANDRA - Apache Cassandra Database Practice Test

CASSANDRA Skills 4