This document provides an overview of distributed databases and the Yahoo! Cloud Serving Benchmark (YCSB). It discusses NoSQL databases Cassandra and HBase and how YCSB can be used to benchmark their performance. Experiments were conducted on Amazon EC2 using YCSB to load data and run workloads on Cassandra and HBase clusters. The results showed Cassandra had lower latency and higher throughput than HBase. YCSB provides a way to compare the performance of different databases.