Elasticsearch is a distributed, open-source search and analytics engine that is built on Apache Lucene and developed in Java. It is used for storing, searching, and analyzing large amounts of structured and unstructured data from various sources and use cases, such as observability, security, and enterprise search.
Elasticsearch works by creating and managing indices, which are collections of documents that have similar characteristics. Each document is a basic unit of information that can be a web page, a log entry, a tweet, or any other kind of data. Each document is stored as a JSON object and has a unique ID. Each document also has one or more fields, which are the key-value pairs that contain the actual data.
Elasticsearch allows you to perform and combine many types of searches on your data, such as full-text search, term-based search, geo-search, and more. You can also use Elasticsearch to perform aggregations, which are operations that process your data and provide summaries or statistics. For example, you can use aggregations to count the number of documents, calculate the average value of a field, or find the most frequent terms in your data.
Elasticsearch is designed to be scalable, resilient, and fast. It can run on a single node or hundreds of nodes with petabytes of data. It distributes the indices and queries across the nodes in the cluster for load balancing and fault tolerance. It also uses inverted indices with finite state transducers for full-text querying, BKD trees for storing numeric and geo data, and a column store for analytics. All these features enable Elasticsearch to provide rapid results and handle high volumes of data.