Rohit Swami
India Resume ↗

Rohit Swami · 10 long reads

Writing

Long reads on the kind of work I do, from flaky tests and fast pipelines to retrieval, and on the problems inside the products I have built. Each has figures you can push around.

Engineering notes

  1. 01A test that always fails isn't flakyTesting · 9 minFailure rate ranks the wrong tests. What flakestat measures instead, why its verdicts wait for evidence, and the times it fooled itself before it could fool anyone else.
  2. 02Ten times faster, mostly by doing lessData engineering · 6 minI rebuilt a graph engine from R to Python and Polars, and it got ten times faster on 80% less memory. Very little of that came from changing languages.
  3. 03Push, don't pollReal-time systems · 5 minGetting a notification from a background job to a browser in under 100 milliseconds is easy once. The hard parts arrive when it has to happen for everyone at once.
  4. 04Spot instances without the 3am pageCloud infrastructure · 5 minSpare cloud capacity is cheap until it's taken back. Interruptions, checkpoints, retries and the spot/on-demand mix behind a batch pipeline bill that came down by 28%.
  5. 05Drawing a graph that's too big to drawVisualisation · 5 minSpatial indexes, culling, level of detail and a single event listener: the unglamorous techniques that make a huge biological network feel instant.
  6. 06Retrieval is the hard partGenAI · 6 minWhen a RAG system gives a bad answer, the model usually takes the blame. More often it was handed the wrong context. Embeddings, chunking and approximate search, seen from the retrieval side.

Building my own products

  1. 07Counting days the way the government doesCitizenDays · 7 minAustralia, Canada, the UK, the US and the Schengen area all limit how long you can be away, and no two count a day the same way. How CitizenDays reads the rules like code, and why it is a day stricter than one official calculator on purpose.
  2. 08A ledger its own server can't readClearOwe · 6 minClearOwe keeps track of money between people. It works offline, follows you to a new phone and shares a balance by link, while the server in the middle learns almost nothing. The three problems that took more thought than the cryptography.
  3. 09Marked like the real thingPart 107 · ASVAB · CitizenOz · 6 minThree exam-prep apps, for the FAA drone licence, the US military's enlistment test and the Australian citizenship test, run on one engine. What it takes for practice to predict the real exam honestly, and why the readiness score is hard to flatter.
  4. 10A WhatsApp export is not a file formatYAPD · 6 minYAPD turns an exported chat into a Wrapped-style recap, and the chat never leaves the browser. Most of the engineering went into reading a format nobody designed, and into letting a language model quote people without ever misquoting them.

Earlier, on Medium

And four peer-reviewed papers, listed on the front page.