Flipkart is a leading example of Solr. It has more than 900k users and sees more than 20k searches per second. Flipkart product search has a backbone of 175 million listings, ~250 million documents, and ~5,500 categories. The major challenge was real-time results, ranking, autocompletion, high-update rates, and inverted index. It has become a huge success by using Solr for product searches for its e-commerce business.