Features

Cross-cutting capabilities that span multiple subsystems. Each page focuses on what the feature does, the code paths that implement it, and where to extend it.

Feature	Source roots	Summary
Search	server/.../search, server/.../action/search	The classic full-text and structured search path
Indexing	server/.../action/bulk, server/.../index/shard	The bulk + single-doc write path with backpressure
Aggregations	server/.../search/aggregations, x-pack/.../analytics	Bucket + metric + pipeline aggregations
Vector search	server/.../index/codec/vectors, libs/simdvec	Dense vector indexing and ANN search
ESQL	x-pack/plugin/esql	The piped query language and execution engine
Ingest pipelines	server/.../ingest, modules/ingest-*	Pre-index processor chains
Index lifecycle (ILM/SLM)	x-pack/plugin/ilm, x-pack/plugin/slm	Hot/warm/cold/frozen rollover and retention
Cross-cluster search and replication	server/.../transport/RemoteClusterService.java, x-pack/plugin/ccr	Federation across clusters
Security	x-pack/plugin/security, x-pack/plugin/identity-provider	AuthN/AuthZ, audit, FIPS
Machine learning	x-pack/plugin/ml, x-pack/plugin/ml-package-loader	Anomaly detection, data-frame analytics, NLP inference
Inference and semantic search	server/.../inference, x-pack/plugin/inference	Inference services + semantic_text field
Snapshot lifecycle and stateless	x-pack/plugin/stateless, x-pack/plugin/searchable-snapshots	Object-storage-backed indices

User-visible features overlap with what the systems layer provides. The split here is roughly: systems = "how", features = "what users can do".