Core Concepts

Lessons in this group, roughly in build order:

• documents — A document is the unit of indexing and retrieval in Elasticsearch: a single JSON object stored in an…
• indices — An index is a named collection of documents with one mapping and one set of settings, physically realized…
• fields-data-types — Every field in a document has a declared data type that decides how it is indexed, what queries work on…
• mappings — A mapping is the schema of an index: the definition of each field’s type, how it is analyzed, and how it…
• inverted-index — The inverted index is the core data structure behind full-text search: a sorted dictionary mapping each…
• shards-replicas — A shard is a self-contained Lucene index holding a slice of an index’s documents; a replica is a full copy…
• nodes-cluster — A node is a single running Elasticsearch process; a cluster is a set of nodes that share a cluster name,…
• segments — A segment is an immutable mini-index inside a shard: a self-contained inverted index (plus doc values and…
• near-real-time-search — Near real-time (NRT) means an indexed document becomes searchable a short, bounded time after it is…