The HLD interviewDeep dives
Your deep dive listed three great options. Why did it earn nothing?
0%
Page 12
More questions.
Core conceptsValet key
Why does a valet get a key that can’t open the boot?
0%
Networking and APIsPush, not poll
Why poll 2,880 times a day to catch 8 orders?
0%
Data and storageAborted read
Why did your autopay fail when your wallet held ₹1,000 all along?
0%
Caching fundamentalsRound trips
Why does a page from Virginia take 660 ms before its first byte?
0%
Messaging and streamsExactly-once
If exactly-once delivery is impossible, how do payments happen only once?
0%
Distributed coordinationGC pauses
Your server froze 36 seconds holding a 30-second lock. What breaks?
0%
Running in productionLock queue
Adding one column takes a millisecond. Why was checkout down for 85 seconds?
0%
Why is it slow? Performance anti-patternsRound trips
Your cart’s data is 16 KB. Why does fetching it take 240 ms?
0%
SecuritySign-in
Could a quiz app use your token to sign in as you?
0%
Multi-tenant SaaSConnection pools
A pooled connection remembered acme. Why did zenmart’s request see acme’s rows?
0%
Architecture stylesWho owns the flow
Your order is stuck. Why does nobody know where?
0%
System design trade-offsPolling
A million apps poll every 30 seconds. Why are 95% of requests wasted?
0%
Key technologiesBatching
Why can one GPU stream 64 chats almost as fast as one?
0%
Common patterns1-D indexes
Why does a latitude index read a strip across the whole city?
0%
InfrastructureWorker numbers
A frozen pod wakes up still minting as worker 37. What breaks?
0%
Search & discoveryFreshness
Why would you check a weekly blog 10,080 times between posts?
0%
Storage & mediaOffline plays
Nine days offline, 212 songs played. How do the artists still get paid?
0%
Social & feedsLearning
You skip a video after one second. Why is your next batch different?
0%
Real-time & collaborationBackscatter
Spam got through. Why must you never bounce it back to the sender?
0%
Location & mapsUploads
Why can’t the phone just stream GPS to the server?
0%
E-commerce & bookingPrice quotes
You saw ₹59,400. Why might checkout say ₹61,200?
0%
Payments & fintechHot accounts
One account takes 5,200 postings a second. Why can’t one row cope?
0%
Data, analytics & monitoringPercentiles
The dashboard says p99 is 281 ms. Why do users wait nearly two seconds?
0%
Developer platformsFlaky tests
Thirty tests each fail 1% of the time. How often is the pipeline red?
0%
AI & LLM systemsCost
Why does every step of an AI agent cost more than the last?
0%