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Designing a Rate Limiter for SDE-2 Interviews: Token Bucket vs Sliding Window, With the Trade-offs Spelled Out

"Design a rate limiter" is one of the most common system design questions in SDE-2 loops, and it's easy to underestimate. Almost everyone can say "use a token bucket". Fewer people can explain why the

devinterviewmasterhq.hashnode.dev

Anish Ansari1d ago · 7 min read

System Design Drill Day 11: The Transactional Outbox Pattern

Almost every Laravel checkout controller has the same two lines: save the order, then dispatch a job. It works nearly every time. If Redis hiccups between those two lines, the order is paid and the em

blog.anishansari.com.np

DevInterviewMaster2d ago · 8 min read

How to Estimate in a System Design Interview: Back-of-the-Envelope Math That Actually Helps

Almost every system design interview has a moment where the interviewer says, "Okay, how much traffic are we talking about?" Many candidates then do one of two things. They skip estimation entirely an

devinterviewmasterhq.hashnode.dev

Anish Ansari3d ago · 7 min read

System Design Drill Day 10: Circuit Breakers, Timeouts and Degradation

The payment gateway starts timing out. The HTTP client retries, the queue retries, and workers pile up waiting on calls that won't come back. Soon pages that have nothing to do with payments are slow

2 blog.anishansari.com.np

Ethan Miller2d ago · 2 min read

How to Answer “Tell Me About a Time You Failed” in an Interview

“Tell me about a time you failed” is one of the most uncomfortable behavioural questions. Many candidates try to avoid it by giving a fake failure or a hidden strength, like working too hard. Intervie

way2ask-interview.hashnode.dev

Gowtham Muthuvel4d ago · 8 min read

Why (a, b) -> a - b Is a Bug in Java Comparators

If you've solved enough LeetCode problems in Java, you've written this: PriorityQueue<Integer> minHeap = new PriorityQueue<>((a, b) -> a - b); PriorityQueue<Integer> maxHeap = new PriorityQueue<>((a,

gowthammuthuvel.hashnode.dev

Anish Ansari4d ago · 7 min read

System Design Drill Day 9: Idempotency Keys for Payments and Retries

A customer taps "Pay" on a shaky mobile connection. The charge goes through on the server, the response never reaches the phone, and the app retries. Whether the customer is now charged twice depends

4 blog.anishansari.com.np

Anish Ansari5d ago · 10 min read

System Design Drill Day 8: Distributed Locks with Redis and Fencing Tokens

One unit of a hot SKU is left, and two customers press "Buy" at the same moment on two different app servers. Both see "1 in stock", both checkouts succeed, and one of them gets an apology email. A mu

10 blog.anishansari.com.np

Anish Ansari6d ago · 8 min read

System Design Drill Day 7: Rate Limiting APIs, Logins and OTPs with Redis

Someone finds your OTP endpoint and starts hammering it. Every call sends an SMS, and you pay for each one. Rate limiting fits into a half-hour interview and still touches algorithms, shared state and

blog.anishansari.com.np

RONI DAS6d ago · 6 min read

1.16 Million Writes a Second: Sharding a Chat App's Messages (System Design Interview in 30 Days, Day 5)

The chat app we sized on Day 2 stores 100 billion messages a day. Divide that by the 86,400 seconds in a day and you get about 1.16 million new messages every second, around the clock. Every one of th

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