what database ElasticSearch uses to store data
Elasticsearch internally uses a custom NoSQL database for storing its data. It is built on top of the Apache Lucene library, which is not a database itself but a high-performance, full-featured text search engine library. Elasticsearch organizes data in a structure optimized for search and analysis operations, rather than using traditional relational databases (like MySQL or PostgreSQL). Please also note that it does not use NoSQL databases like MongoDB or Cassandra.
Key Points About Elasticsearch's Data Storage:
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Document-Oriented: Elasticsearch stores data as JSON documents. Each document is a basic unit of information that can be indexed. This document model is flexible, allowing for the easy addition of new fields without requiring a modification of a schema.
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Inverted Index: To facilitate fast search, Elasticsearch uses an inverted index provided by Lucene. This index maps every term to the documents containing it, enabling very quick full-text searches.
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Distributed Nature: Elasticsearch automatically distributes data (documents) across multiple nodes (servers) in a cluster to ensure redundancy, scalability, and high availability. This distribution also enables Elasticsearch to execute search and aggregation operations across all these nodes in parallel, improving performance.
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Sharding and Replication: Elasticsearch splits data into shards, which are then distributed across the cluster's nodes. It also replicates these shards to protect against hardware failure and improve query performance by load-balancing read operations across replicas.
The combination of these characteristics makes Elasticsearch a powerful tool for full-text search, real-time analytics, and data visualization (through integration with tools like Kibana). It's worth noting that while Elasticsearch manages its data storage internally, it's designed to be agnostic of the underlying hardware storage system, meaning it can operate on various types of disk storage systems, including SSDs and HDDs, depending on the deployment environment's configuration.