Cassandra Practice Test

Which component in Cassandra directly contributes to writing transactions efficiently?

1. Key cache

2. MemTable

3. Commit log

4. SStable

The correct answer is: Commit log

In Cassandra, the component that directly contributes to writing transactions efficiently is the commit log. The commit log is designed to ensure durability in the face of failures by recording every write operation as it occurs. When a write request is received, it is first written to the commit log to guarantee that no data is lost if a crash or failure occurs immediately after the write. This approach of using a commit log allows Cassandra to process write operations quickly because the write can be acknowledged to the client immediately after it has been recorded in the commit log, without needing to wait for the data to be flushed to disk or stored in a more complex structure. Following this, the data is typically stored in memory in a structure known as a MemTable before eventually being written to disk in the form of SSTables (Sorted Strings Tables). The commit log effectively decouples the write operations from the more resource-intensive processes of data storage, thereby optimizing the overall performance of write transactions within Cassandra.