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

Segment merging under control

Lucene segments are written once and read many times, and data structures, apart from the information about the deleted documents that are held in one of the files, can be changed. After some time, when certain conditions are met, the contents of some segments can be copied to a bigger segment, and the original segments are discarded and thus deleted from the disk. Such an operation is called segment merging.

You may ask yourself, why bother about segment merging? There are a few reasons. First of all, the more segments the index is built from, the slower the search will be and the more memory Lucene will need. In addition to this, segments are immutable, so the information is not deleted from them. If you happen to delete many documents from your index, until the merge happens, these documents are only marked as deleted and are not deleted physically. So, when segment merging happens, the documents that are marked as deleted are not written into the new segment...