Q191. How would you write a robust, idempotent automation script?
A production script should be safe to re-run, fail clearly and clean up after itself. ```bash #!/usr/bin/env bash set -euo pipefail workdir=$(mktemp -d) cleanup() { rm -r...
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Q192. Explain the rule of three, five and zero, plus undefined behaviour.
The rule of three: if a class needs a custom destructor, copy constructor or copy assignment operator, it probably needs all three, because they manage the same resource....
Q193. What are lambda expressions or arrow functions?
**Arrow functions** (also known as "lambda expressions") provide a concise syntax for writing function expressions in JavaScript. Introduced in ES6, arrow functions are o...
Q194. Explain two-phase commit and its drawbacks.
Two-phase commit, 2PC, is an atomic commit protocol for transactions spanning multiple databases or resource managers. Phase one, prepare: the coordinator asks every part...
Q195. Explain TCP congestion control.
TCP congestion control keeps the sender from overwhelming the network. The sender maintains a congestion window, cwnd, and sends at most the minimum of cwnd and the recei...
Q196. What is data leakage in machine learning?
Data leakage is when information unavailable at prediction time seeps into training, producing optimistic validation scores that collapse in production. Common sources: -...
Q197. How do you revoke a JWT before it expires?
A stateless JWT cannot be un-issued, so revocation needs supporting state. Options: - Denylist: store revoked token identifiers (`jti`) until their `exp`, and check on ea...
Q198. How does Kafka provide exactly-once semantics?
Kafka combines two features: - Idempotent producer: each producer gets a producer id and sequence numbers. The broker deduplicates retries within a session, so a network ...
Q199. What is a first class function?
In JavaScript, **first-class functions(first-class citizens)** mean that functions are treated like any other variable. That means: 1. You can assign a function to a vari...
Q200. How would you scale a relational database as traffic grows?
Scaling relational databases follows a progression, because a single node eventually hits CPU, memory or I/O limits. 1. Optimise first: fix queries, add indexes, tune the...