Idempotent consumers, without the ceremony
What actually happens when the same message arrives twice, and the smallest set of changes that makes a consumer safe to retry.
Where the depth lives
Notes from building backend systems: what I designed, what broke, and the reasoning I wish I had written down the first time.
Topics
Four threads I keep pulling on
Not tutorials. Working notes: what I tried, what it cost, and what I would tell myself before starting.
AI
Agents, LLMs, RAG and AI architecture — what I build, test and break.
System Design
Distributed systems, databases, messaging, caching and scaling.
Code & Snippets
Working references from Java, Spring, PostgreSQL, Kafka, Redis and Kubernetes.
Architecture Lab
Full write-ups from problem to trade-offs, with the diagrams to match.
Latest
Recent engineering notes
Newest first. Some are finished thoughts, others are still moving.
Designing a URL shortener
The classic interview system, built small and measured: where the reads go, what the cache is for, and the one decision that made everything else easy.
What I got wrong about tool calling — and why designing tools like an API fixed most of it
I assumed the model would use the tools sensibly. It did not. What changed once I started designing tools the way I design an API: narrower inputs, typed arguments, and error messages written for the model rather than for me.
Indexes I added, then removed
Three index changes that looked obvious in review and cost more than they saved once real traffic arrived.
A Bloom filter in forty lines of Java
The smallest useful implementation, the two parameters that matter, and how wrong the false-positive rate gets when you guess them.
Sharding vs partitioning
Two words used interchangeably in meetings, and the operational difference that makes them not the same thing at all.
Redis caching: the invalidation I got wrong first
Cache-aside looked simple until two writers raced. What I changed, and what I would measure before adding a cache next time.
RabbitMQ vs Kafka
Not a benchmark. A comparison of the questions each one makes you answer: about ordering, replay, consumers and who owns the offset.
Java concurrency, the parts I keep relearning
Executors, CompletableFuture and virtual threads — written down so I stop rediscovering the same three pitfalls.
Why I am learning AI agents
Less about the hype, more about a specific kind of repetitive work I would like a program to take off my hands.
Vibe coding lessons
A month of letting an assistant write most of the first draft: where it saved hours, and where it cost me a weekend.
Next
Have a system worth arguing about?
I am always up for a conversation about architecture, trade-offs, or a bug that refuses to die.
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