You know that Elasticsearch is a Java application and, because of that, it runs in the Java Virtual Machine. Each Java application is compiled into a so-called byte code, which can be executed by the JVM. In the most general way of thinking, you can imagine that the JVM is just executing other programs and controlling their behavior. However, this is not what you will care about unless you develop plugins for Elasticsearch, which we will discuss in Chapter 9, Developing Elasticsearch Plugins. What you will care about is the garbage collector—the piece of JVM that is responsible for memory management. When objects are de-referenced, they can be removed from the memory by the garbage collector. When the memory is running, the low garbage collector starts working and tries to remove objects that are no longer referenced. In this section, we will see how to configure the garbage collector, how to avoid memory swapping, how to log the garbage collector behavior...