System Design

Pages, write-ahead logs, B-trees and LSM-trees, with write, read and space amplification measured on a page store and a miniature LSM, and PostgreSQL 18 measured on page layout, HOT updates, bloat and WAL bytes.

A cache from first principles: a map plus a recency list, TTLs without a timer per key, LRU against sampled and random eviction measured on a Zipf workload, and the stampede that takes your database down.

Designing a rate limiter from requirements to API: token bucket against fixed window with the boundary burst measured, an injected clock, thread safety, and what .NET, Java, Go and Rust’s libraries really do.

What layered, hexagonal and clean architecture really say, where they disagree, and how dependencies get inverted in C#, Java, Go and Rust, with .NET’s container lifetimes and captive dependencies shown in running code.

Strategy, adapter, decorator, middleware, observer, builder and state machines in C#, Java, Go and Rust, with the patterns each language feature deleted, and a measured look at what changes when you add a case.

Locks, atomics, channels, ownership and actors compared on one counter in C#, Java, Go and Rust, measured; what a data race really is, which bugs each model makes impossible, and which it quietly keeps.

How C# and Java exceptions, Go’s error values and Rust’s Result carry one failure through a service, what each compiler checks, what failure costs, measured, and where to handle errors, log them and turn them into responses.

How to design types so impossible data can’t be built: sum types, exhaustive matching, newtypes, parsing at the boundary and typestate, in C#, Java, Go and Rust, with what each compiler actually says when a case is missed.

Why implementation inheritance breaks, shown in running Java code; how interfaces, Go’s embedding, Rust traits and plain functions abstract without it; and what static and dynamic dispatch cost, measured in Rust, Go and C#.

What each SOLID principle originally said, who said it, and how it gets misread. Liskov substitution broken in running code and in Java and .NET’s own libraries, dependency inversion measured with the Go build tool, and each principle in C#, Java, Go and Rust.