Skip to content

Today’s Drill · 23 Oct

Account reads are slow on a store built for fast writes

Face-offStretch · SDE-2+7 min
The situationNext Drill at 05:30 IST

Your fintech app keeps customer balances in an LSM-based key-value store on 3 nodes. It takes only 3,000 writes per second of about 200 bytes, but reading one account sometimes takes 40 ms at p99. Product now wants range reports, joins with transactions and "balance at 5 pm yesterday".

  • 7minAbout 7 minutes
  • 3–5Questions, one at a time
  • 1Short report at the end

Trains: API and data model, Estimation, Cost and trade-offs

One a day

The same Drill for everyone, every day

A new Drill goes live at 05:30 IST. Everyone gets the same one, so you can compare notes with a friend. A Drill does not come back until all the others have had their day.

Today’s Drill is live23 Oct

Goes live at 05:30 IST

Hours are in India time (IST).

How a Drill goes

Three steps, about seven minutes

No slides and no theory first. You work through one real situation.

  1. Step 1: Read the situation

    You get the facts: what broke, and the numbers. No theory first. Decide what you would look at first.

  2. Step 2: Answer in your own words

    An interviewer asks 3 to 5 questions, one at a time. You type what you would check and do, and why.

  3. Step 3: Get a short report

    It lists the points you covered and the ones you missed, and says why each one matters.

What it trains

Today: API and data model and Estimation and Cost and trade-offs

Every Drill is tied to a skill that interviewers test. This is what stays with you after the report.

After the reportSample

  • In the report

    Your own words, quoted

    The report puts what you said next to what was good and what was missing.

  • In My Prep

    Gaps go to your journal

    A point you missed becomes an entry in the mistakes journal in My Prep, so you can come back to it.

  • In a Fix it round

    Try the weak part again

    When something was missing, a short Fix it round lets you answer that part once more.

A Solid or Strong result also marks the skill as re-checked on your skill map in My Prep. Your score does not change: it shows that you practised the skill again.

Do it together

What your friend sees

After your report you can share a short message: today’s Drill, how many points you covered, and a link. It has no name and none of your answers.

You can also send today’s Drill before you play. That message has the title, the date and the link, and nothing else.

After the Drill

More ways to practise

Seven minutes. Start now.

One real situation, 3 to 5 questions, and a short report at the end.