This is our fourth book about Elasticsearch and, again, I am fascinated by how quickly Elasticsearch is evolving. We always have to find the balance between describing features marked as experimental or work in progress, and we have to take the risk that the final code might behave differently or even ignore some of the interesting features. The second edition of this book has quite a large number of rewrites and covers some new features; however, this comes at the cost of the removal of some information that was less useful for readers. With this book, we've tried to introduce some additional topics connected to Elasticsearch. However, the whole ecosystem and the ELK stack (Elasticsearch, Logstash, and Kibana) or Hadoop integration deserves a dedicated book.

Now, it is time to say thank you.

Thanks to all the people who created Elasticsearch, Lucene, and all the libraries and modules published around these projects or used by these projects.

I would also like to thank the team that worked on this book. First of all, thanks to the ones who worked on the extermination of all my errors, typos, and ambiguities. Many thanks to all the people who sent us remarks or wrote constructive reviews. I was surprised and encouraged by the fact that someone found our work useful. Thank you.

Last but not least, thanks to all the friends who stood by me and understood my constant lack of time.