Design a Top-K search words service

Q: Design a Top-K search words service

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Question

Scenario

Design a service that tracks user search queries and returns the Top-K most searched words/queries.

Requirements

Functional

API to record a search query event (e.g., user searches "iphone 16").
API to fetch Top-K queries.
Support a time window variant:
- (a) all-time Top-K
- (b) Top-K over the last N minutes/hours (trending)

Non-functional

High write QPS (search events), low latency reads for Top-K.
Scalable horizontally.
Reasonable correctness (define whether exact or approximate is acceptable).

Clarifications to address

What is a “word” vs “query” (full string)?
Case-folding, normalization, stop words, punctuation.
Deduping (e.g., multiple searches by same user) or count every event.
Multi-region and eventual consistency expectations.