Global Search Engineering

A standard SQL database cannot handle "Fuzzy" search across 100 million documents efficiently. For that, we need an Inverted Index. Elasticsearch is the industry leader for this.

1. The Inverted Index

Instead of mapping: Document -> Words, it maps Word -> List of Documents. This allows the search engine to find every document containing "Architecture" in microseconds, no matter how large the dataset is.

2. Sharding & Replicas

Elasticsearch is distributed by design. You can split your search index into multiple **Shards**. To handle more traffic, you add **Replicas**. This makes it perfect for e-commerce sites like Amazon where search is the heart of the business.

4. Interview Mastery

Q: "How do you keep Elasticsearch in sync with your SQL Database?"

Architect Answer: "The most robust way is **CDC (Change Data Capture)**. We listen to the SQL Server 'Transaction Log.' Every time a record is updated, a tool like Debezium or a Kafka worker pushes that change to Elasticsearch. This ensures that the search engine is never more than a few milliseconds out of sync with the 'Source of Truth' DB."