Understanding Elasticsearch caching
One of the very important parts of Elasticsearch, although not always visible to the users, is caching. It allows Elasticsearch to store commonly used data in memory and reuse it on demand. Of course, we can't cache everything—we usually have way more data than we have memory, and creating caches may be quite expensive when it comes to performance. In this chapter, we will look at the different caches exposed by Elasticsearch, and we will discuss how they are used and how we can control their usage. Hopefully, such information will allow you to better understand how this great search server works internally.
The filter cache
The filter cache is the simplest of all the caches available in Elasticsearch. It is used during query time to cache the results of filters that are used in queries. We already talked about filters in section Handling filters and why it matters of Chapter 2, Power User Query DSL, but let's look at a simple example. Let's assume that...
