Elasticsearch is a modern, fast, distributed, scalable, fault tolerant, and open source search and analytics engine. Elasticsearch leverages the capabilities of Apache Lucene, providing a new level of control over how you can index and search even huge sets of data. This book covers intermediate and advanced functionalities of Elasticsearch and walks you through its internals including caches, the Apache Lucene library, and its monitoring capabilities. You'll learn about practical usage of Elasticsearch configuration parameters and how to use the monitoring API. With this book, you'll delve into Elasticsearch's query rewrite, query template, bulk operation, document grouping, and function score queries. You will also learn how to improve user search experience, index distribution, segment statistics, and merging. By the end of the book, you will be able to enhance Elasticsearch's performance and create your own Elasticsearch plugins.