Databases

You’re three months into a new project. You have a PostgreSQL database for your core data, Redis for caching, Elasticsearch for search, MongoDB for “flexible” documents, and TimescaleDB for metrics. Five different systems, five different failure modes, five different backup strategies. Your on-call rotation is a nightmare. Here’s the thing - Postgres alone could have handled four of those five jobs. Maybe all five. I’m not saying Postgres is the only database you’ll ever need. I’m saying it should be the last database you add to your stack, not the first one you try to replace. There’s a reason it keeps winning. ...

“Redis is single-threaded.” You’ve heard this in every system design interview, every blog post, every tech talk. It was true in 2009. It’s not true anymore - and hasn’t been since 2020. But the way Redis adopted multithreading is more interesting than just flipping a switch. It’s a story about knowing exactly where your bottleneck is and only parallelizing that part. Why Single-Threaded Was the Right Call When Salvatore Sanfilippi built Redis in 2009, he made what seemed like a strange choice - a single-threaded event loop for a high-performance database. But it wasn’t strange at all. It was the smartest possible design for an in-memory data store. ...

You spin up a single Redis instance, throw your session data in it, and everything works great. Then your app grows. One day Redis goes down for 30 seconds during a deploy, and every user gets logged out. Your manager asks: “Why don’t we have high availability?” You Google “Redis HA” and find Sentinel, Cluster, sharding, replication, pipelining - and suddenly a key-value store feels as complex as a distributed database. ...

You’re in a system design interview. You say “we’ll use PostgreSQL” and immediately follow it with “and we’ll shard it across 16 nodes.” The interviewer asks: “How much traffic are you expecting?” You don’t have a number. You just sharded because it sounded like the senior thing to do. Here’s the thing - most teams shard too early. A single PostgreSQL node can handle far more than people think. The decision to shard should come from actual numbers, not vibes. This post gives you those numbers. ...

A deep, practical guide to SQL vs NoSQL databases. Not textbook definitions - real trade-offs, real examples, and a decision checklist that actually works.

When Redis changed its license in 2024, the community forked it into Valkey. Two years later, there is a clear answer on which one most teams should use.

SQLite runs in billions of devices and is the most deployed database in the world. It is also quietly powering a surprising number of production web applications that used to need Postgres.

PostgreSQL has gone from “solid relational database” to the default choice for almost every new project. Here is why that happened and whether the crown is deserved.