Datomic
The free database designed for immutable values and a time-aware information model.
Datomic is a database built on immutable values: writes append facts rather than overwriting rows, so every past database value remains available for query, debug, and replay. It targets systems where provenance, decision tracing, and as-of queries are central requirements, such as ledgers, settlement pipelines, compliance, supply chain, healthcare, and legal records. Corrections are additive, and audit trails stay in sync with the data.
It uses an E/A/V+T information model with covering indexes (EAVT, AEVT, AVET, VAET), pull queries for document- and graph-shaped reads, first-class transaction entities for querying history itself, and built-in change data capture. The distributed Peer/Client architecture separates storage (pluggable durable service), transactor (writes), and query (local immutable snapshots) for horizontal read scaling. It is built in Clojure, with tools such as d/sync and the transaction report queue supporting event sourcing.
Datomic is offered in two editions: Datomic Pro, which runs on-premises or in the cloud with pluggable storage, and Datomic Cloud, which is AWS-native with automated deployment of processes, caches, auto-scaling groups, load balancing, and web and AWS Lambda entry points. The homepage describes Datomic as free; no further plan or pricing details are stated.
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