• Store data so that they, or another application, can find it again later (databases)
• Remember the result of an expensive operation, to speed up reads (caches)
• Allow users to search data by keyword or filter it in various ways (search indexes)
• Send a message to another process, to be handled asynchronously (stream pro‐ cessing)
• Periodically crunch a large amount of accumulated data (batch processing)
- For example, there are datastores that are also used as mes‐ sage queues (Redis), and there are message queues with database-like durability guar‐ antees (Apache Kafka).
