WARNING: The 2.x versions of Elasticsearch have passed their EOL dates. If you are running a 2.x version, we strongly advise you to upgrade.
This documentation is no longer maintained and may be removed. For the latest information, see the current Elasticsearch documentation.
In Life Inside a Cluster, we introduced the shard, and described it as a low-level worker unit. But what exactly is a shard and how does it work? In this chapter, we answer these questions:
- Why is search near real-time?
- Why are document CRUD (create-read-update-delete) operations real-time?
- How does Elasticsearch ensure that the changes you make are durable, that they won’t be lost if there is a power failure?
- Why does deleting documents not free up space immediately?
What do the
optimizeAPIs do, and when should you use them?
The easiest way to understand how a shard functions today is to start with a history lesson. We will look at the problems that needed to be solved in order to provide a distributed durable data store with near real-time search and analytics.