Relational databases are useful for their transactional and query capabilities but do not scale linearly. Distributed "shared nothing" architectures like Hadoop MapReduce are more scalable by making work independent and parallelizable. However, real-world problems often require sharing data between processes. A common pattern is to use MapReduce for bulk processing and loading data, then use databases or other technologies for interactive queries and iterative jobs. Choosing the right data storage technology depends on an application's specific needs.