Apache CouchDB vs eXist-db

Apache CouchDB is a free document database that stores named documents and lets applications read and update them through a RESTful HTTP API. Documents can contain fields and binary attachments without following a fixed schema. Its query engine supports views made with JavaScript map functions and optional reduce functions. Incremental replication synchronizes databases in both directions between peers, including after disconnections; the project describes this as useful for offline-first applications across servers, phones, and browsers. PouchDB can replicate with CouchDB from mobile devices and web browsers. A cluster can present one logical database across multiple servers or virtual machines for added capacity and high availability. CouchDB uses an append-only file design, and its documentation describes document updates as ACID and all-or-nothing. Security features include administrator accounts, basic and cookie authentication, reader access controls, and JavaScript validation of document updates. Replicas may retain conflicting revisions for manual or automated resolution. CouchDB is self-hosted on servers or virtual machines, as a single node or cluster, and is licensed under Apache License 2.0.

eXist-db is a free, open-source NoSQL document database and application platform centered on XML. Its native engine stores textual or binary documents without requiring a database schema, and it is designed for self-hosted deployment on Linux, macOS, or Windows. The product implements XQuery 3.1, though some features and functions are unsupported, and RESTXQ lets developers deploy RESTful services from XQuery annotations. Its interfaces include REST-style HTTP, SOAP, XML-RPC, and WebDAV. A browser-based IDE provides syntax coloring, code completion, and error checking for application artifacts. Full-text search uses an implementation-specific Apache Lucene approach rather than the W3C XQuery and XPath Full Text 3.0 specification. Security extends Unix permissions with access control lists and external authentication realms. The software is licensed under the LGPL for academic, non-commercial, and commercial use. The documentation lists Java 8 for versions 3.x–6.x or Java 21 for version 7.x, about 500 MB of disk space, and at least 512 MB of memory.