ETL Interview Questions

Pipeline Architecture (124)

• 45 Minutes Turned Into 3.5 Hours - medium - Spark jobs are running. Just not fast enough.
• 600 Million Events a Day - hard - 600 million events a day. Two years of retention.
• A Clean Number for Every Merchant - hard - Raw payment logs in. Clean merchant summaries out.
• A Million Cars Phoning Home - hard - Every vehicle is a sensor. Deploy the pipeline to catch it all.
• Analysts Are Slowing the Store Down - medium - Orders placed. Data warehouse hungry.
• A New Column on a Billion Rows - hard - Add and backfill a new column to a billion-row production table with zero downtime.
• A Shared Drive Full of Contracts - medium - Buried in PDFs. The data is in there somewhere.
• A Stream All Day and a File at Midnight - hard - Real-time and batch. Same pipeline. No compromises.
• Badging Items That Already Sold Out - hard - Same-day delivery. The features have to be faster.
• Basel, CCAR, and Monday Morning - medium - The regulator does not accept 'eventually consistent.'
• Bikes Before Rush Hour - hard - Bikes in, bikes out. The city needs to predict demand.
• Credit for Every Touch - medium - They saw the ad, clicked the email, then bought. Who gets credit?
• Doubling Every Six Months - hard - Tuesdays are quiet. Black Friday is not.
• Eight-Hour-Old Positions - hard - Positions shift by the second. The math cannot lag.
• Eight Teams, Eight Latencies - medium - Millions of gamers. The architecture decision changes everything.
• End of Day Is Too Late - medium - Every swipe tells a story.
• Equities, ETFs, and the SEC - hard - Fractional shares, multi-currency, point-in-time. All of it.
• Event System for Multiple Consumers - hard - One event, many hungry consumers.
• Every Dataset Needs a Paper Trail - hard - The FDA has opinions about your data pipeline.
• Every Deal Is a Financial Transaction - hard - Real money on the table. Reconstruct every hand.
• Every Device, Every Impression - hard - Every ad seen. Every second watched. Real-time.
• Every Device Has Its Own Dialect - medium - Three sources. Three formats. Same workout.
• Every Firm Formats It Differently - medium - The regulator changed the format. Again. Handle it.
• Every Format Imaginable - hard - PDFs, HL7, JSON. All of it lands in the same lake.
• Everyone Wants the Same Data, Differently - hard - How you store it decides how fast you can read it.
• Every Region Exports Its Own Way - medium - Sales data, BigQuery, Dataflow. Make it all sing.
• Every Scan, Every Parcel, Every Pin Code - medium - Out for delivery. Delivered. Except the events arrived backwards.
• Fifty Thousand Retailers - medium - Retail data at CPG scale. Every SKU, every store.
• The Box That Won't Fit the Data - hard
• Five Times the Traffic, Five Times the Bill - hard - Scale up when needed. Do not bankrupt the team.
• Five Years of Cron Jobs - hard - Half the jobs run on cron. Half run on events. All of it has to move.
• Flying Blind Until Midnight - hard - Intraday risk, full lineage. The regulator is watching.
• Four Teams, One Topic, No Agreement - hard - Everybody is writing to it. Nobody documented it. Now production is fragile.
• Greenfield Build for Six Sources - hard - Infrastructure as code. Meaning as a service.
• Half a Million Rental Cars - medium - Every vehicle is reporting. Every rental matters.
• The Identity Problem - hard - Old systems. New demands. The same customer appears under three different names.
• Listens From Everywhere, Counted Once - hard - Phones, tablets, laptops. And some of them report late.
• Live Viewers, Live Billing - hard - The stream is live. The data cannot wait.
• Near-Real-Time Trending Dishes Dashboard - hard - The dish rankings update faster than the kitchen.
• Nested Docs, Flat Reports - medium - Two databases. One direction. No data left behind.
• Nightly Exports Are Too Slow - medium - Healthcare claims change constantly. The warehouse cannot fall behind.
• 4,500 Stores Before Sunrise - medium - The shelves open at 7. The data better be there.
• Not Every Team Can See Every Row - hard - Everyone can see the bucket. Not everyone should.
• One Bill Across Three Clouds - medium - AWS, Azure, GCP. Three bills. One truth.
• One Earthquake, Ten Thousand Tweets - hard - The firehose is on. Separate signal from noise.
• Out of the Data Center - medium - The on-prem servers are not getting any younger.
• The Speed Layer - medium - Dashboards can't wait for raw logs. Something has to happen upstream.
• Prove the Number Is Right - hard - Bad data in fintech is not just messy. It is expensive.
• Real Data, Fake Patients - hard - Dev needs production data. HIPAA says absolutely not.
• The Register Never Sleeps - medium - Every swipe lands in the warehouse. The table has to stay current without breaking.
• Recommendations Now, Royalties Later - medium - The catalog updated. Did anyone notice?
• Replicate It Without Breaking It - hard - The source changed. The lake needs to know immediately.
• Risk Models on Week-Old Data - medium - Loan approved. Loan denied. Every decision is an event.
• SaaS API Connector with Incremental Sync - medium - The API has rate limits. You have deadlines.
• Same-Day Sales, Every Store - medium - The cash register data needs to be queryable by morning.
• The Living Table - medium - Data lands continuously. History must survive every update.
• Score It Before It Clears - hard - The fraudsters move fast. Your pipeline has to move faster.
• Ship Before Fraud Finishes Checking - hard - The claim looks clean. The fraud model disagrees.
• Six Hours to Miss a Deadline - medium - The rebuild works. It just doesn't finish in time.
• Six Hours to Refresh Every Number - medium - Ratings change. The incremental model has to keep pace.
• Six Million Rows Before the Market Opens - medium - One massive CSV. Millions of timestamps.
• Six Sources, One Platform - medium - ADF orchestrates. Unity Catalog governs. Nothing leaks.
• Sixty Minutes, Every Hour - medium - Every hour, on the hour. No excuses.
• Stores and the Site, Together - hard - The registers never stop ringing.
• Store, Site, and Distributor - medium - Sales data is piling up. Someone has to make sense of it.
• The Acquisition Still Taking Bookings - hard - Two systems, two schemas. One truth.
• The Agency That Changes the Columns - medium - The schema changed overnight. Again.
• The Analysts Cannot Touch Production - medium - Production is the source. Analytics needs its own copy.
• The Analyst Who Saw the Salary Data - hard - Two incidents. One shared lake. The access model was never designed, just assumed.
• The API Drip Feed - medium - The API gives you 100 records at a time. You need millions.
• The Bad Row That Broke the Dashboard - medium - Bad records cannot reach the warehouse.
• The Binding and the Claim - medium - Policies are instant. Claims take their time.
• The Booking That Came Three Ways - hard - PMS, OTA, and website all think they took the reservation first.
• The Boutique That Sold in Six Currencies - hard - Every sale is real. The rate it was converted at depends on who is asking.
• The Bucket Full of Resumes - medium - A thousand resumes. Structured data inside each one.
• The Carrier Moving to Azure - medium - Claims arrive messy. The medallion cleans them up.
• The Claim That Picks Its Own Lane - medium - Three entry points. Different workflows. All must route correctly.
• The Clicks We Throw Away - hard - Every tap, swipe, and scroll. At scale.
• The Clock That Runs Two Ways - hard - Nightly batch and live events. One dashboard.
• The Consent Stitcher - medium - Consent was given. Or was it? Stitch the records together.
• The Dashboard and the Attribution Model - hard - Streaming and batch. One pipeline to rule them.
• The Decision Before the Door Closes - hard - The window to stop it is smaller than you think.
• The Distributor Filing Problem - medium - Hundreds of suppliers. One warehouse. One deadline.
• The Event Pile - hard - 600 million clicks a day. The budget is not infinite.
• The Fare Aggregator - medium - Airfares shift every minute. Catch the best ones.
• The Fleet That Never Stops - hard - Every truck is talking. Not everyone can hear them yet.
• The Leaderboard That Costs $25K a Month - hard - Product wants it live. Engineering has a price tag.
• The Meal Kit That Knows You - medium - What they ordered says a lot about what they want next.
• The Migration That Cannot Break Morning - hard - It all works today. Moving it without losing a single report is the hard part.
• The Models Going Stale - hard - The model is only as good as what you feed it.
• The Panel and the Set-Top Boxes - hard - Set-top boxes tell you who watched. Projection tells you how many.
• The Patients We Cannot Move - hard - Patient data stays local. Insights have to be global.
• The Points Arrive Two Days Late - medium - The bank data shows up late. The rewards were already sent.
• The Provider That Sometimes Sleeps - medium - The models run at dawn. The data has to be there first.
• The Query That Used to Be Fast - medium - Queries used to be fast. Something changed.
• The Queue That Wouldn't Stop Growing - medium - 500,000 messages behind and the number keeps climbing.
• The Revenue That Was Wrong for Two Weeks - medium - Nobody caught it until the CFO asked a question. Design the system that catches it first.
• The Sale That Needs to Land Now - medium - Three channels feeding one view. Not all of them speak the same language.
• The Signals That Power Recommendations - medium - Fresh signals, many teams, one pipeline.
• The User Who Asked to Be Forgotten - hard - Users want their data erased. Completely.
• The Vendor Who Never Warns You - medium - Every month, something is different. The dashboards have no idea.
• The What-If Machine - hard - A million slots. A thousand campaigns. Every combination matters.
• The Whiteboard Exercise - medium - Marker in hand. Draw the whole thing.
• Thirty Cities, One Forecast - hard - Five cities. Five data formats. One prediction.
• Thirty Countries, One Solvency Number - hard - Premiums collected globally. Losses happen locally.
• Thirty Million Unique Jobs a Year - hard - One press run, many orders. Group them right.
• Thousands of Practices, One Dataset - hard - Patient records in, operational insights out.
• Three Providers, One Workout - hard - The same ride, reported three times.
• Three Regions, One Finance Team - hard - Payments from everywhere. One consistent report.
• Three Regions, One Report - hard - Three regions, billions of payments, one merchant summary by 6 AM.
• Towers and Phones, Same Story - hard - Tower signals meet app events. Somewhere in between is the truth.
• Traders, Risk, and the Regulators - medium - Markets move in milliseconds. The pipeline has to keep up.
• Two Hundred Million Redirects - medium - Billions of clicks. One tiny code. Two very different clocks.
• Two Million Boxes by Monday Morning - hard - Shipped, maybe. Delivered, debatable.
• Two Systems, One Room Count - hard - Two booking systems. Rooms do not duplicate themselves.
• Two Ways to Catch a Change - medium - Two ways to watch the database. Each has a cost.
• Two Years of Every Click - hard - Every click, every aisle, every day for two years.
• Two Years of Clicks, Cheap - hard - Two years of clicks. Every query has to be affordable.
• What Everyone Is Watching - hard - Someone is watching. Capture everything.
• What Should We Recommend Tonight - hard - They ordered pad thai twice. That means something.
• Where Is Every Truck, Right Now - medium - Trucks are moving. Every ping counts.
• Which Promotion Is Actually Working - hard - Was the promotion worth it? The data knows.
• Who Is Churning and Why - medium - Subscribers churn. The pipeline cannot.
• Who Saw the Ad Twice - hard - TV and digital. Same viewer, two measurement worlds.