When you are in trouble and your cluster works slower than usual and uses large amounts of CPU power, you know you need to do something to make it work again. This is the case when the Hot Threads API can give you the information necessary to find the root cause of problems. A hot thread in this case is a Java thread that uses a high CPU volume and executes for longer periods of time. Such a thread doesn't mean that there is something wrong with Elasticsearch itself; it gives you information on what can be a possible hotspot and allows you to see which part of your deployment you need to look more deeply at, such as query execution or Lucene segments merging. The Hot Threads API returns information about which parts of the Elasticsearch code are hot spots from the CPU side or where Elasticsearch is stuck for some reason.

When using the Hot Threads API, you can examine all nodes, a selected few of them, or a particular node using the /_nodes/hot_threads or /_nodes/{node or...