Databases: Design, Access, and Scale Databases are the backbone of most software. A clean design saves time later, while poor choices cost performance and money. The core idea is to match how data is stored with how it is used.
Design choices Start from the questions your app answers: who owns a post, which comments belong to it, when a user last logged in. Choose a model: relational (tables and keys), document (collections of nested data), or wide-column (more flexible rows). Normalize to avoid duplication, but denormalize when reads are heavy. Use indexes and materialized views to speed common queries. Access patterns Define the typical queries and transactions first. Index the fields used in filters and joins: e.g., users.id, posts.author_id, comments.post_id. Use connection pools and limit long-running reads; add a caching layer for hot data. Scale Vertical scaling adds power to one machine, but has limits. Horizontal scaling adds more machines: replicas for reads, shards for writes. For critical work, consider distributed transactions carefully; many apps use eventual consistency with clear boundaries. Plan backups, monitoring, and disaster recovery from the start. Example A small blog: users, posts, comments. A relational design with foreign keys makes it easy to enforce consistency; indexes on posts.author_id and comments.post_id speed lookups. Getting started Sketch a simple data model on paper. List the 5 most common queries; design indexes for them. Pick a database family that fits: relational for strong consistency, document for flexible schemas, or a column store for analytics. Trade-offs Normalization reduces updates but can slow reads with joins; denormalization speeds reads but needs more updates. Caching helps, yet requires good invalidation rules. Strong consistency is clear and safe, but may limit throughput under heavy load. Real-world tips Measure early: use simple benchmarks for your key queries. Use explain plans or profiling to find slow parts. Prepare for growth with read replicas and regular backups. Key Takeaways Start with data needs, then pick a data model that fits read and write patterns. Design for the main queries and keep an eye on indexes and caching. Plan for scale early with a clear strategy for replication, sharding, and backups.