Databases

Every backend you will ever build keeps its truth in a database, and most performance problems, data bugs and interview questions come back to one. This path explains what a database actually does with your query, how it scales through replication and sharding, the SQL that interviews keep asking, and how the three most common non-relational databases work, each drawn as a diagram you can follow.

Read the first part in order. The SQL and the NoSQL sections can be read in any order once you have it.

How a database works#

What happens between pressing Enter and getting rows back, and the promises a database makes about your data.

Scaling a database#

What to do when one database is not enough, in the order you should do it, and how to make sure you never lose the data while you are at it.

SQL for interviews#

Joins you can see, the ten patterns most SQL rounds draw from, and a cheat sheet for the night before.

Beyond relational#

Three databases you will meet in almost every system design, how each one works inside, and the one decision that makes or breaks each of them.