Book Image

Mastering Elasticsearch 5.x - Third Edition

By : Bharvi Dixit
Book Image

Mastering Elasticsearch 5.x - Third Edition

By: Bharvi Dixit

Overview of this book

Elasticsearch is a modern, fast, distributed, scalable, fault tolerant, and open source search and analytics engine. Elasticsearch leverages the capabilities of Apache Lucene, and provides a new level of control over how you can index and search even huge sets of data. This book will give you a brief recap of the basics and also introduce you to the new features of Elasticsearch 5. We will guide you through the intermediate and advanced functionalities of Elasticsearch, such as querying, indexing, searching, and modifying data. We’ll also explore advanced concepts, including aggregation, index control, sharding, replication, and clustering. We’ll show you the modules of monitoring and administration available in Elasticsearch, and will also cover backup and recovery. You will get an understanding of how you can scale your Elasticsearch cluster to contextualize it and improve its performance. We’ll also show you how you can create your own analysis plugin in Elasticsearch. By the end of the book, you will have all the knowledge necessary to master Elasticsearch and put it to efficient use.
Table of Contents (20 chapters)
Mastering Elasticsearch 5.x - Third Edition
About the Author
About the Reviewer
Customer Feedback

Query rescoring

One of the great features provided by Elasticsearch is the ability to change the ordering of documents after they are returned by a query. Actually, Elasticsearch does a simple trick-it recalculates the score of top matching documents, so only part of the document in the response is reordered. The reasons why we want to do this can vary. One of the reasons may be performance. For example, calculating target ordering is very costly because scripts are used and we would like to do this on the subset of documents returned by the original query. You can imagine that rescore gives us many great opportunities for business use cases. Now, let's look at this functionality and how we can benefit from using it.

What is query rescoring?

Rescoring in Elasticsearch is the process of recalculating the score for a defined number of documents returned by the query. This means that Elasticsearch first takes N documents for a given query (or the post_filter phase) and calculates their score...