Spring Boot Interview Question : Building Trending Search Queries at Scale

You are building the “Trending Searches” feature for a large e-commerce platform.

Every day, the search system processes:

• 500 million search queries

• Millions of unique search terms

• Queries coming from multiple regions

• Multiple search clusters

The product team wants:

Design a system that returns the Top K most frequently searched queries in near real-time.

The API should expose:

Response:

[
  {
    "query": "iphone 17",
    "count": 1254300
  },
  {
    "query": "air fryer",
    "count": 985000
  }
]

Initial Implementation

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The algorithm requires loading all queries into memory. For example:

The map grows with every unique query: Map<String,Integer>

Problems:

• High memory usage

• Cannot handle continuous streams

• Requires full dataset before calculation

• Expensive sorting, sorting has O(N log N) time complexity

The system should separate ingestion, aggregation, and serving. This prevents expensive computations from happening every time a user requests trending searches.