Replication in Elasticsearch refers to the process of creating and maintaining copies of shards across multiple nodes in a cluster. Replication provides fault tolerance and high availability by ensuring that data is available in the event of a node failure. Elasticsearch can replicate shards across multiple nodes to provide redundancy and ensure that data is available even if one or more nodes fail.
Each shard in Elasticsearch can have one or more replicas. By default, Elasticsearch creates one replica for each shard. Replicas are stored on separate nodes from the primary shard, and are updated in real-time as changes are made to the primary shard.
Replication can also improve search performance by distributing query load across multiple nodes. When a search query is executed, it is broadcast to all nodes that contain a replica of the shard being searched. This allows Elasticsearch to parallelize search operations across multiple nodes, improving performance and scalability.
Overall, replication is an important mechanism in Elasticsearch that provides fault tolerance, high availability, and improved search performance. By replicating shards across multiple nodes, Elasticsearch can ensure that data is available in the event of a node failure and improve search performance by distributing query load across multiple nodes.