ArcadeDB is a high-performance, multi-model database system supporting graph, document, key-value, time-series, vector, and full-text data models. It exposes multiple query languages (SQL, Cypher, Gremlin, GraphQL) and wire protocols (HTTP, Bolt, PostgreSQL, MongoDB, gRPC). The architecture is modular: a core engine (storage, indexing, query execution) with pluggable server plugins for protocols, replication (Raft-based HA), and observability. It features advanced indexing (LSM-tree, hash, vector quantization, sparse vectors, full-text BM25), time-series with PromQL and downsampling, and graph analytical views with CSR compression. Python bindings allow embedded use. The codebase demonstrates strong engineering with extensive use of interfaces, design patterns, comprehensive test coverage (including issue-specific regression tests), and automated CI/CD with performance benchmarks. It is actively maintained with low technical debt and a clean architecture.
OrientDB is a multi-model NoSQL database management system supporting document, graph, object, and relational data models within a single engine. It provides ACID transactions, a SQL-like query language, distributed clustering with automatic sharding and replication, full-text and spatial indexing via Lucene, and a Gremlin graph traversal API. The system is implemented in Java and organized into modular components: a core storage engine with pluggable index structures (SB-Tree, hash, Lucene), a binary client-server protocol, an HTTP REST API, and a web-based administration studio (AngularJS). It includes enterprise features such as backup/restore, metrics monitoring, and security auditing. The architecture follows a plugin-based server model, allowing extensions for authentication, indexing, and custom commands. External dependencies include Dropwizard Metrics, Lucene, Gremlin/TinkerPop, and various compression libraries.