Cassandra Practice Test

What is one effect of performing compaction on SSTables?

1. It compromises data consistency

2. It can lead to slower reads during the process

3. It helps in faster reads once complete

4. It increases the size of the SSTables

The correct answer is: It helps in faster reads once complete

Compaction is a critical process in Apache Cassandra that involves merging multiple SSTables (Sorted String Tables) into a single SSTable. This process has several beneficial effects, particularly regarding read performance. When compaction is completed, it reduces the number of SSTables that need to be accessed to retrieve data. Since data is stored in sorted order, fewer SSTables typically mean that lookup times during reads are decreased, resulting in faster data retrieval. By consolidating smaller SSTables, Cassandra can optimize the way data is organized, thus streamlining read operations. In contrast, the other options highlight potential concerns during or as a result of the compaction process. For example, while compaction may incur some temporary slowdown in read operations during its execution, the end result leads to improved performance. Similarly, it does not compromise data consistency; rather, it is designed to maintain it. Lastly, compaction generally reduces the overall size of the data on disk due to the reorganization and removal of deleted data, rather than increasing it.