Learn AI Coding, AI Agents and Software Engineering by Building Real Projects
We killed, froze and cut off the leader of a real etcd cluster, 66 times. A killed one was replaced in a median 1.2 seconds, and two nodes once both called themselves leader for about 0.8 s. How Raft elects, replicates and commits, and why it stays correct.
This laptop’s clock, kept in sync by NTP, was tens of milliseconds off, and 187 ms off after a sleep. We measured what a gap like that does to a database that keeps the last write, then built the clocks that fix it: Lamport, vector, hybrid, TrueTime.
One etcd node cut off from its cluster, measured. During the cut its linearizable reads and writes got no answer, and its serializable reads all answered out of date. Plus what CAP proves, what “2 of 3” gets wrong, and what consistency costs day to day.
A remote call can succeed, fail, or tell you nothing. Measured on real HTTP: lost replies charge customers more than once, three of four default clients wait 150 s or more, and retries multiply 243 times over five layers, then keep a simulated server down.
Cache-aside to write-behind, what Redis 8 really does when it fills up, the invalidation race and the lease that closes it, three fixes for a stampede measured against doing nothing, and the HTTP caching headers most people misread.
Putting the whole series together — chunking, embedding, indexing, hybrid retrieval, reranking and the evaluation loop that tells you whether any of it worked. The part where the decisions stop being independent.
Qdrant starts with no authentication at all. What to turn on before it faces anything, how read-only and scoped access work, which metrics are worth an alert, and how to plan capacity from the arithmetic in this series.
What happens when one machine isn’t enough. Shards split the data, replicas copy it, and the consistency factors decide what “written” and “read” mean when a node is missing.
How to back up a collection, how to restore one, and the alias swap that lets you rebuild an index with a new model or new parameters while traffic keeps flowing. The operational part you need before your first incident, not after.
Segments, the optimiser, the write-ahead log and what mmap really does. How a collection is laid out on disk, what has to be in RAM for search to be fast, and why your first query after a restart is the slow one.