Final answer:
The correct answer is d) Partition Indexes are sorted partition keys mapped to their SSTable offsets, which details how partition indexes function in systems like Apache Cassandra.
Step-by-step explanation:
The correct statement among the options given is: d) Partition Indexes are sorted partition keys mapped to their SSTable offsets. This statement is accurate as it describes how partition indexes work in database systems that use SSTables, such as Apache Cassandra. Partition indexes are indeed used to map sorted partition keys to the corresponding SSTable offsets, which allows the system to quickly locate the data associated with a given partition key.
Statement a) Row cache is an in-memory cache is also correct. It refers to the cache that holds the actual rows of data in memory to avoid disk reads on subsequent accesses of the same data. Statement b) Key Cache maps recently read partition keys to specific SSTable offset accurately defines the purpose of the key cache, which is to speed up data retrieval by avoiding the need to read the partition index from disk. However, statement c) Compaction offsets keep the offset mapping information for compressed blocks, while it relates to compaction processes, does not match common terminologies used to describe these processes.