CASSANDRA Performance and Tuning 2

Question 1

What does 'hinted handoff' do when a replica node is temporarily down?

Accepted Answer

The coordinator stores the write as a hint and replays it to the node when it recovers

Answer

Hinted handoff lets the coordinator temporarily store missed writes for a down replica and deliver them once that node comes back online, improving write availability.

Question 2

What is 'write amplification' in the context of Cassandra compaction?

Accepted Answer

The multiple of data written to disk relative to the actual data inserted due to compaction rewriting SSTables

Answer

Write amplification occurs because compaction must read and rewrite SSTables to merge them, causing significantly more disk I/O than the original writes.

Question 3

What does the 'nodetool tpstats' command display?

Accepted Answer

Thread pool statistics showing active, pending, and blocked tasks

Answer

nodetool tpstats shows the state of all Cassandra internal thread pools, helping identify bottlenecks when pending or blocked counts are high.

Question 4

What is 'key cache' in Cassandra and how does it improve performance?

Accepted Answer

Caches partition key to SSTable offset mappings, reducing disk seeks for frequently accessed partitions

Answer

The key cache stores the position of a partition key within an SSTable, so Cassandra can skip the index lookup and seek directly to the data on subsequent accesses.

Question 5

What does the 'LOCAL_QUORUM' consistency level ensure in a multi-datacenter Cassandra deployment?

Accepted Answer

A quorum of nodes within the local data center must respond

Answer

LOCAL_QUORUM satisfies quorum using only replicas in the same data center as the coordinator, avoiding cross-DC latency while still providing strong consistency locally.

CASSANDRA - Apache Cassandra Database Practice Test

CASSANDRA - Apache Cassandra Database Practice Test

CASSANDRA Performance and Tuning 2