What is the process of "Compaction" in Cassandra?

Compaction in Cassandra is the process of merging SSTables (Sorted String Tables) to optimize data storage and improve read performance. During compaction, multiple SSTables are combined into a single SSTable, which helps to reduce the total number of SSTables on disk. This reduction in the number of SSTables leads to more efficient data access, as the system has fewer files to read during queries.

Merging SSTables does several things: it consolidates fragmented data, removes tombstones (markers for deleted data), and optimizes the underlying storage layout. As a result, compaction not only saves disk space by eliminating duplicate data but also ensures that queries are processed faster because there are fewer files to traverse.

This process is essential in Cassandra's performance tuning, as it impacts both write and read operations by enhancing the throughput and latency for read queries. By understanding that compaction is primarily about merging SSTables, it's clear why this choice is the correct understanding of the term within the context of Cassandra's architecture and functionality.