Q271. Explain database normalisation and the common normal forms.
Normalisation organises columns into tables to reduce redundancy and update anomalies. The common normal forms: - 1NF: atomic values, no repeating groups, each row unique...
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Q272. Explain the TLS handshake and what it protects.
TLS provides confidentiality, integrity and authentication for a connection. In TLS 1.3 the handshake is one round trip before application data. 1. The client sends a Cli...
Q273. Explain virtual memory and paging.
Virtual memory gives each process the illusion of a large, contiguous address space, independent of physical RAM. The CPU's memory management unit translates virtual addr...
Q274. When should you prefer composition over inheritance?
Inheritance is an is-a relationship: `Dog extends Animal` because every dog is an animal. Composition is a has-a relationship: `Car` holds an `Engine`. Inheritance gives ...
Q275. What is the difference between vanity metrics and actionable metrics?
Vanity metrics look impressive but do not guide decisions: total registered users, page views, cumulative downloads. They only go up, lack context and cannot be tied to a...
Q276. How do you design a reliable A/B test?
Start with a clear hypothesis and a primary metric tied to the business, plus guardrail metrics for regressions. Key steps: 1. Define the unit of randomization, usually t...
Q277. Explain precision and recall and when to prefer each.
Precision is the fraction of predicted positives that are truly positive: TP / (TP + FP). Recall, or sensitivity, is the fraction of actual positives that were found: TP ...
Q278. How does an orchestration tool like Airflow schedule data pipelines?
Airflow models a workflow as a DAG: a directed acyclic graph of tasks with dependencies. A scheduler parses DAG files, creates DAG runs per schedule interval, and queues ...
Q279. How do you implement a distributed lock with Redis?
A common implementation is SET key value NX PX ttl. NX sets the key only if it does not exist, and PX gives the lock an expiry so a crashed holder cannot deadlock the sys...
Q280. What is the $lookup stage and what are its trade-offs?
$lookup performs a left outer join against another collection in the same database. The basic form matches localField against foreignField and returns matches in an "as" ...